Nutrients – Chapter 21

Most any nutrient formula (fertilizer), regardless of its contents, will grow cannabis. But what quality will the cannabis be, and what are the residual health concerns? With the proper nutrient formula and growing conditions, medical cannabis can reach its genetic growth potential. 

Healthy cannabis plants produce high yields.

Healthy cannabis organically grown by DoobieDuck attracts birds and other wildlife.


Cannabis needs the non-mineral nutrients carbon, hydrogen, and oxygen to manufacture food and grow. Carbon (CO2) in the air is fixed via photosynthesis. Hydrogen atoms that are building blocks come almost totally from water. Oxygen from the atmosphere is used in respiration and plant processes. The rest of the elements (called mineral nutrients), are absorbed from the growing medium and nutrient solution. Supplemental nutrients supplied in the form of a fertilizer help medicinal cannabis to reach its maximum potential. 

Nutrients must be available to roots in order to be absorbed. Nutrients occur in many chemical combinations and forms (called compounds) that are comprised of two or more nutrients’ ions joined together via positive (anion) and negative (cation) attractions.* The compounds release nutrients for uptake by roots under specific conditions. The proper nutrient formula delivered at the proper pH and EC concentration makes nutrients available for uptake. *An anion is an ion with a negative charge because it has more electrons than protons. A cation is an ion with a positive charge because it has more protons than electrons.

Well-managed life—microbes, bacteria, fungi, etc.—in organic soil interacts with naturally occurring nutrients to make them available for uptake by roots. Properly mixed and alimented soils with high fertility require very little supplemental fertilizer. For example, during the flowering stage, outdoor gardeners in Humboldt County, California, add just 2 handfuls of bat guano to grow 10-pound (4.5 kg) plants in living organic soil.

Nutrients are grouped into 3 categories: macronutrients or primary nutrients, secondary nutrients*, and micronutrients or trace elements. ** Each nutrient in the above categories can be further classified as either mobile or immobile. Solving nutrient-deficiency problems is much easier when you know which nutrients are mobile or immobile. 

*Some confusion exists on what the secondary nutrients are, but they are generally considered macronutrients as well as secondary macronutrients, and are measured the same way as a percentage of the overall mix. 
**Trace elements are micronutrients measured in ppm. 

best cannabis nutrients

Mobile nutrients are able to move (translocate) from one part of the plant to another as needed. When a nutrient shortage occurs, mobile nutrients travel to the area to solve the deficiency. For example, nitrogen accumulated in older leaves translocates to younger leaves to solve a deficiency. Mobile nutrients show deficiency symptoms on older, lower leaves first. Nitrogen will show a deficiency on older leaves because it is a part of essential enzyme structure and has to be replaced as these enzymes are denatured and disposed of. Mobile nutrients include nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg).

Immobile nutrients either stay at their destination or move very little once assimilated and transported. Immobile nutrients include calcium (Ca), boron (B), chlorine (Cl), cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), silicon (Si), sulfur (S) and zinc (Zn). Deficiencies of immobile nutrients show symptoms first in younger leaves. These nutrients do not translocate to new growing areas as needed. They remain deposited in their original place in older leaves. 

Other elements—Barium (Ba), Cadmium (Cd), Chromium (Cr), Lithium (Li), Palladium (Pd), and Vanadium (V)—may be necessary for plant growth and health. These elements should be available in low concentrations.

Toxic Nutrient Conditions

Too often gardeners give their medical cannabis gardens too much tender loving care. This care and enthusiasm is kindled by countless nutrient and additive advertisements. As a consequence, medical cannabis gardeners frequently overapply fertilizers and additives, creating toxic soil conditions. Often the solution to this problem is to leach the built-up nutrients out of the growing medium with copious quantities of water. This will wash away excess nutrients that have built up in the soil and created toxic conditions. An overabundance of nutrients (fertilizer salts) in the growing medium disrupts the medium’s chemical balance. This imbalance causes some nutrients to become unavailable for uptake by roots and other nutrients to be oversupplied.

Leaching the substrate works well for most nutrient problems, but it does not solve all nutrient problems. For more information please see specific nutrients.

Leaching Growing Mediums

To leach* soil or substrate, add enough water (it takes a lot!) to the medium to wash out excess fertilizer (nutrient) salts. For a container that holds 1 gallon (3.8 L) of water, add enough water to make sure it is full—until water drips out the bottom. Then apply 1 additional gallon of water (3.8 L,) and allow 1 gallon (3.8 L) to drain out the bottom of the container. Do this a total of 7 times. Once a total of 7 gallons (26.5 L) of water has been added and drained, the process is almost complete.

Add 1 more gallon (3.8 L) of water that includes the correct ratio and concentration of fertilizer. The entire process must be completed within 20 minutes or the excess of water will drown the roots. The process can be done 2 or 20 times, as long as it is completed within 20 minutes. I repeat: the container must drain completely within 20 minutes. “Drain completely” means drain to a point at which the water is held against gravity within 20 minutes. This practice is not overwatering. 

*Water is used to leach fertilizer salts from a growing medium. Just before harvest, plants and soil are flushed to remove excess nutrients in plant tissue. 

Note: See chapter 9, Harvest, Drying & Curing, for more info about leaching the substrate and flushing nutrients out of medical cannabis plants before harvest. See chapter 23, Container Culture & Hydroponics, for more information on leaching hydroponic mediums and water-based hydroponics.

Leach substrates to wash away nutrient buildup.

In order to measure nutrients in solution, you will need an accurate, calibrated EC (electrical conductivity) meter and an accurate, calibrated pH meter.

nitrogen (N)mobile
phosphorus (P)mobile
Potassium (K)mobile
calcium (Ca)immobile
magnesium (Mg)mobile
sulfur (S)semimobile
zinc (Zn)immobile
iron (Fe)semimobile
manganese (Mn)immobile
boron (B)very immobile
copper (Cu)semimobile
molybdenum (Mo)mobile
chlorine (Cl)immobile
cobalt (Co)immobile
nickel (Ni)mobile
selenium (Se)semimobile
silicon (Si)immobile
sodium (Na)mobile / immobile

Fertilizer contents are listed on the container. Read them carefully to ensure that your plants are receiving a balanced nutrient formula.

These seedlings are suffering from nitrogen deficiency.

The pale leaf on the left is nitrogen.

The nitrogen level is low in flowering fertilizer formulas, causing older leaves to yellow.


Macronutrients are the elements that the plants use most and must be present at all times for growth to grow well. Most fertilizers usually show nitrogen (N), potassium (P), phosphorous (K) as (N-P-K) percentages in big numbers on the front of the package. They are always listed in the same N-P-K order. These nutrients must always be in an available (soluble) form to supply cannabis with the building blocks for rapid growth. Nitrogen is the nutrient most often found deficient.

Nitrogen (N)—mobile (essential)

About: High levels of nitrogen are needed during vegetative growth, but lower levels are needed during seedling, clone, and flowering growth stages. Reducing nitrogen levels causes earlier flowering and increased abscisic acid (hormone) levels.

Nitrogen regulates the cannabis plant’s ability to make proteins essential for new protoplasm in the cells, and many other functions. It is mainly responsible for leaf and stem growth, as well as overall size and vigor. Nitrogen is most active in young buds, shoots, and leaves. Cannabis absorbs nitrogen mainly in the form of ammonium (NH4+), which is assimilated very quickly into mainly amino acids, and nitrate (NO3-)—the nitrate form of nitrogen—is assimilated more slowly into most everything else. Small organ-ic molecules also supply nitrogen. Be careful when using ammonium; too much can burn plants. Hydroponic fertilizers use slower-acting nitrate and mix it with ammonium. The proper balance keeps the rhizosphere pH more stable, and high ammonium levels influence taste of harvest. 

Deficiency: Nitrogen is the most common cannabis nutrient deficiency in greenhouses, indoors, and outdoors. Low levels of nitrogen deficiency often go un-noticed. Deficiencies progress as follows: 

First there is a lightening and slight yellow coloration to older mature leaves followed by leaf death or drop. Leaves lose luster, turning slightly pale. Stunting can also be seen when there has been a slight deficiency for a time. Acute deficiency will result in decreased flowering.

Leaf margins may discolor. Leaves continue to yellow and may curl, develop brownish spots, and, as deficiency progresses, start to drop. Growth slows on shorter plants with smaller leaves and narrower stems. Yellowing of leaves progresses upward on plants. Signs of premature flowering appear on sickly plants. Yield is substantially diminished.

Nitrogen-deficient leaf

This photo of ‘Pakistani’ leaves shows the progression of nitrogen deficiency (clockwise from top left). (MF)

Cause: Nitrogen is highly soluble and easily washed out of growing mediums. It must be replaced regularly, especially during vegetative growth. Decaying organic matter and soil life may consume available nitrogen in soil and deplete it faster than roots can take it up.

Nitrogen is used quickly during rapid growth, and mild deficiency could occur; even if it is available, roots may not be able to supply nitrogen fast enough. Nutrient levels inside plants catch up when growth slows. The cause could also be inadequate nitrogen in the fertilization schedule or when using a growing medium with a low CEC (cation exchange capacity) that was not designed for use with the nutrient formula. Diseases such as Fusarium and Pythium can cut fluid flow and the supply of nitrogen, but they have specific symptoms apart from nitrogen depletion. 

Confused with: Potassium deficiency. Reddish stems and leaf undersides caused by potassium deficiency can be misinterpreted in cannabis varieties that naturally have reddish-purple stems and petioles. 

Solution: Leach growing medium with a slightly more concentrated nutrient solution. Fertilize with the proper soluble high-nitrogen fertilizer that has the proper ratio of ammonium (NH4+) and nitrate (NO3-)—the nitrate for the growing medium. Organic sources of soluble high-nitrogen fertilizers include blood meal, seabird guano, fish emulsion, compost teas, and more. Check and correct pH in the root zone. Leaves should green up in 3 to 5 days. Severely affected leaves may not recover and should be re-moved. For faster results in foliage, foliar feed with a soluble, dilute, high-nitrogen fertilizer. Soil application is also necessary when foliar feeding, because foliar applications do not translocate. Even though nitrogen is mobile when plants are foliar fed, it stays in the leaves. 

Excess: First, older bottom leaves turn lush, dark green, and supple. As the overdose advances, leaves in the middle and top of the plant are affected. The weak foliage is susceptible to temperature and humidity stress, diseases, and pest attacks. Stems weaken and fold if stress is allowed to progress. As the excess progresses, the water transport system becomes restricted and foliage turns brownish-copper. Leaves become thickened and brittle, excess NH4 causes Ca deficiency. Excess levels of nitrogen in harvested plants cause the dried cannabis to taste “green” and burn poorly when smoked.

Cause: Nitrogen overdose is seldom a problem unless soil is loaded with the nutrient or too much was applied via the fertilizer mix. 

Confused with: Excess nitrogen is not usually confused with anything unless salt burn becomes an issue. Some have related it to viral infections. 

Solution: Leach growing medium with a dilute fertilizer solution. Severe problems require heavy leaching to carry away all the toxic elements. Leach as per “Leaching Growing Mediums”. Add a dilute complete fertilizer. Cut back on nitrogen dose if plants remain excessively green. Results should appear in 3 to 5 days, possibly earlier in hydroponic gardens.

Do not withhold nitrogen in subsequent fertilizing after leaching or when flowering. The nitrogen in the mix must be reduced but not removed. The main issue for cannabis cultivation is when the level of NH4 is too high. When too much N is applied, especially as NH4, it is moved to the vacuole of the cell and converts to nitrite or nitrosamines or both—cancer-causing products. Some “experts” say the ratio of nitrogen needs to be 1:1 but the experts I believe find that a more reduced ratio of 1:4 is much better and safer. This provides a balance so that the ratio of nitrogen does not deviate and turn into NH4 quickly.

Phosphorus (P)—mobile (essential)

About: Phosphorus is indispensable for photosynthesis. It is the energy source for plants transferring energy generated in PS and during respiration, from the release of stored energy in carbohydrates. Phosphorus—one of the components of DNA, many being enzymes and proteins—is associated with overall vigor, resin, and seed production. Phosphorus is extremely important to the health of young plants. More than two thirds of the phosphorus absorbed during the cannabis life cycle is taken in during the first quarter of life. The highest concentrations of phosphorus are found in roots’ growing tips, growing shoots, and vascular tissue.

Deficiency: Lack of phosphorus is relatively uncommon and often misdiagnosed. The deficiency is first noticed when the petioles begin to take on a purple hue. Do not confuse with purpling of the main stem, which is indicative of an overall nutrient deficiency. Leaves take on a bluish green hue. Vertical growth slows, as well as lateral development. Dark copper-colored or purple-to-blackish dead blotches start to show on deformed lower leaves after a couple of weeks of deficiency. Dark necrotic spots develop on leaf stems (petioles) as leaves curl down-ward and drop. Severely affected leaves develop a dark bronze or metallic purple color as leaves continue to curl, contort, wither, and drop. Flowering is often delayed, buds are much smaller, seed yield is poor, and plants become more vulnerable to fungal and insect attack.

There is a big difference between petioles and stems when purpling occurs. On petioles this is a clear sign of phosphorus deficiency; on stems this is an overall deficiency indicating under-feeding. This underfeeding can come from many reasons, including lack of nutrients, but also poor water relations, high humidity, anything that slows transport, and overdosing microbes in the root zone as well as soil temp being too high or low, and overwatering. Purpling petioles or stems are NOT associated with a nitrogen deficiency, except where it was part of an overall problem including phosphorus.

Phosphorus deficiency

Cause: When a phosphorus deficiency does occur, the pH has usually drifted up too high, beyond 7.0, which makes the macronutrient unavailable for uptake because it becomes unavailable as it changes ion form. Cold temperatures [below 50°F (10°C)] impair phosphorus uptake. Deficiencies are aggravated by clay and soggy soils. Other causes include acidic growing medium, an excess of iron and zinc, or soil that has become fixated (chemically bound) with phosphates. However, adequate zinc is necessary for proper utilization of phosphorus.

Confused with: Zinc deficiency, cold temperatures.

Solution: Naturally occurring phosphate compounds accessible for uptake by roots are seldom available. Phosphorus is bound in organic compounds and is released via decomposition affected by soil life. Bat guano is a readily available source of phosphorus. Steamed bone meal, barnyard manure, and compost are the next-best sources. Thoroughly mix in the organic nutrients into living soil. Always use finely ground organic components that break down and become available quickly. Prevent deficiencies by mixing a complete organic fertilizer that contains phosphorus into the growing medium before planting. Outdoors, mix fine, steamed bone meal and pulverized rock phosphate into soil the year before planting. 

Use phosphoric acid to lower the pH to within a range of 5.5 to 6.2 in hydroponic units, and lower the EC too. Correct the pH (6.0–7.0 for clay soils and 5.5–6.5 for potting soils) to facilitate phosphorus availability. If the soil is too acidic and an excess of iron and zinc exists, phosphorous becomes unavailable.

Cannabis absorbs inorganic phosphates in ionic form only. Check with your local hydroponic store for appropriate phosphorous-rich, properly formulated nutrient mixtures. Use soluble forms of phosphorus when soil temperatures are below 50°F (10°C). 

Excess: Relatively common, especially during flowering. In fact, an excess of phosphorus is promoted to thicken flower buds and add weight to final harvest. Excess is usually caused by adding too much high-phosphorus fertilizer in an available form. Toxic signs of phosphorus may take several weeks to surface, especially if excesses are buffered by a stable pH. Symptoms manifest in the form of micronutrient deficiencies in zinc, which is the most common, and iron. Also, as phosphorus availability increases, calcium and magnesium availability drops. If signs of zinc and iron deficiencies are present, phosphorus could also be lacking.

Excess chemical-based phosphorus in cannabis buds during flowering causes a “chemical” taste when smoked.

Cause: Many cannabis varieties can tolerate high levels of phosphorus. Avail-able phosphorus builds to toxic levels if heavily applied and not leached from soil.

Confused with: A deficiency of zinc, iron, magnesium, or calcium.

Solution: Raise the pH. Phosphorus does not leach very well so leaching the growing medium has little effect. It just changes form and can combine with calcium to form insoluble compounds.

Potassium (K)—mobile (essential)

About: Potassium helps combine sugars, starches, and carbohydrates, and is essential to their production and movement. Potassium is vital to growth by cell division. It increases the chlorophyll in the foliage and helps to regulate stomata openings so plants make better use of light and air. It is necessary to make proteins that augment oil content and improve flavor in cannabis plants. It also encourages strong root growth and is associated with disease resistance and water intake. The potash form of potassium oxide is (K2O). Soils with a high level of potassium increase a plant’s resistance to bacteria and mold.

Deficiency: Potassium deficiencies are common in indoor gardens, less common in greenhouses, and somewhat common outdoors. Potassium deficiency causes the internal temperature of foliage to climb; beyond 104°F (40°C), it causes protein in cells to burn and degrade. To cool down leaves, evaporate moisture. Evaporation is normally highest on leaf edges, and that’s where the burning takes place. Up to 70 percent of a plant’s energy is “burned” to keep cool. 

Potassium in excess also moves to these far areas, pores at the ends of the veins, and accumulates, causing this burn that is often confused with general salt burn but is not. The chlorosis must be seen first and a dulling in the cuticle layer of the leaf, all on older leaves. Plants with a minor potassium deficiency appear healthy; leaves are a little too green and have a dull tone. Stems thin and branching may increase. Young leaf fringes and tips discolor turning a rusty brown, dehydrating and curling up. Progressively greater numbers of older leaves (first tips and margins, followed by whole leaves) develop rust-colored blotches, turn dark, and die. Stems often become weak, scrawny, and sometimes brittle. Deficient plants become very susceptible to disease and pest attacks. Flowering is retarded and greatly diminished. 

The burned leaf fringes on this ‘Dynamite’ clone have classic signs of potassium deficiency.

Potassium deficiency

Severe potassium deficiency

This soluble plant food lists its ingredients in percentages and explains where they were derived from.

Cause: Potassium is usually present but fixed or bound in humus-rich and clay soils, often locked in by toxic fertilizer (salt) buildup. Excess sodium in the water source that has built up in soil, calcium magnesium and phosphorus and cold weather impair uptake of potassium. 

Confused with: Endema (an abnormal accumulation of fluids) or spots caused by bacteria or fungi. Absorption of magnesium, manganese, and sometimes zinc and iron is also slowed. Burned leaf margins are also caused by low humidity and overall fertilizer (salt) burn. 

Solution: Leach the toxic salt out of the soil by leaching heavily with clean water.

Apply a well-balanced N-P-K fertilizer with high potassium content. Organic gardeners add fast-acting potassium in the form of liquid kelp or potash. Potassium is absorbed quickly and deficiency symptoms should disappear in a few days. Add slow-acting granite dust and greensand to outdoor planting holes.

Excess: Occasionally, too much potassium is a problem, but it is difficult to diagnose because it is mixed with the deficiency symptoms of other nutrients. Excess potassium acidifies the root zone, slows the absorption of calcium, magnesium, and sometimes zinc and iron. Look for signs of toxic potassium buildup when symptoms of calcium, magnesium, zinc, and iron deficiencies appear. 

Cause: Potassium has built up in soil, and too much is now available to roots.

Confused with: Calcium, magnesium, and sometimes zinc and iron deficiencies or general salt burn. However, coco coir gives off large amounts of potassium, which is readily absorbed and locks out calcium and magnesium; the result is calcium and magnesium deficiency symptoms but with tip and later marginal leaf burn from potassium accumulating at these points. True salt burn comes not from too many ions in the tissue but from a reversal of the osmotic gradient, pulling water out of the plants not moving it into the plant. The fix in coco is to increase the EC, not back it up and leach. 

Solution: Leach the growing medium of affected plants with a very mild and complete fertilizer solution. Severe problems require that more water be leached through the growing medium. Leach with a minimum of three times the volume of water for the volume of the growing medium.

Secondary Nutrients

The secondary nutrients—calcium, magnesium, and sulfur—are often grouped with the macronutrients (nitrogen, phosphorus, and potassium) because plants use secondary nutrients in large amounts. Rapid-growing cannabis is able to process more of these nutrients than most general-purpose fertilizers are able to supply. A properly balanced organic or ionic salt hydroponic fertilizer supplies all necessary macro and micro (trace) elements in the proper formulations for maximum results. 

Calcium and magnesium are dissolved in all water sources, usually in large amounts. Lower levels of sulfur are also present in most water supplies. Always take into account the amount of preexisting calcium and magnesium ‘nutrients’ already available in the water supply when fertilizing, especially in hydroponic formulas. Excessive calcium causes “hard water,” a condition that limits nutrient uptake.

If growing in an acidic potting soil or soilless mix, correct the pH of the growing medium to 5.8 with agricultural lime. Calcium is already incorporated into the peat part of the mix. The proper rate of all lime tends to be three to five kilograms per 35 ft3 (3–5 kg per 1 m3). 

With a pH below 6.0, incorporating one cup of fine (flour) dolomite lime per gallon of growing medium ensures adequate supplies of calcium and magnesium. Forms of sulfur are found as compounds in most fertilizers.

Calcium (Ca)—immobile (essential)

About: Calcium is fundamental to cell manufacturing and growth. Calcium is necessary to preserve membrane permeability and cell integrity, which ensure proper flow of nitrogen and sugars. Calcium stimulates enzymes that help build strong cell and root walls. Cannabis must have some calcium at the grow-ing tip of each root. Since calcium has little mobility within the plant, it must be available in the root zone for uptake in order to avoid shortages. Tap water “hardness” is determined by the amount of dissolved calcium and magnesium salts. High levels of calcium help protect plant tissue from pest and disease attacks. But hard water scale contains a considerable amount of calcium carbonate, CaCO3, which is almost insoluble in water. 

Deficiency: Calcium is most often deficient in hydroponic gardens, but this deficiency is rather uncommon in green-houses and indoors. Calcium is abundant in virtually all soils but occasionally lacking outdoors in cool wet climates and acidic soil. Calcium is sometimes deficient in soilless rooting mediums.

Early deficiency causes lower leaves to contort and curl. As the deficiency progresses, symptoms appear relatively quickly, first in lower leaves that develop yellowish-brown irregular spots with a dark brown border that enlarges over time. Often spots are at or near the edge of leaves. Older affected leaves develop yellowish hazy zones and spots around larger necrotic irregular spots. Flower bud development is inhibited, and root tips often die back. The plants are stunted and harvest is diminished. 

Cause: An imbalanced fertilizer with unavailable calcium causes a deficiency. Calcium can be bound or fixed in (acidic) soil and unavailable for uptake. Excess ammonium, magnesium, potassium, and sodium in the root zone impair calci-um uptake. Often, calcium is available in solution and growing medium but unavailable within the plant due to a transport problem (within the plant) caused by environmental conditions. Humidity that is too high or too low impairs transpiration. An EC that is too high, or improper irrigation that causes internal movement of water, will affect calcium uptake and is demonstrated in lower leaves. Excess phosphorus could also be the cause.

Confused with: Root disease, excess nitrogen (ammonium), magnesium, potassium and sodium or deficiencies of iron, potassium and zinc.

Solution: Leach soil and soilless mix with plain or low-EC water to wash out any built-up fertilizer salts that impair calcium uptake. Avert deficiencies in the soil and in most soilless mixes by adding fine dolomite lime (Ca and Mg) or gypsum (calcium sulfate hydrate [CaSO4·2(H2O)]) to the planting mix. Acidic soils often contain low levels of calcium.

Use properly formulated soluble-hydroponic fertilizer that contains adequate available calcium, preferably calcium nitrate. Dissolve one-half teaspoon (2.5 cc) of hydrated lime per gallon of water. Water the deficient plants with calcium-dosed water as long as new deficiency symptoms persist. Remember, damaged tissue will not go away. Or use a complete hydroponic nutrient that contains adequate available calcium. Keep the pH of the growing medium stable. Reverse osmosis filtered water must have calcium added. 

Excess: Leaves wilt, but very little. Excessive amounts of soluble calcium applied early in life can stunt growth. Too much calcium blocks potassium, iron, magnesium, and manganese uptake. If growing hydroponically, an excess of calcium will combine with sulfur in the solution, which causes the nutrient solution to suspend in the water and to aggregate into clumps, which then causes the water to become cloudy (flocculate). Once calcium and sulfur combine, they form a residue [gypsum CaSO4·2(H2O)] that settles to the bottom of the reservoir. 

Cause: Too much available calcium in water or nutrient solution.

Confused with: Deficiency of potassium, magnesium, manganese, or iron.

Solution: Change nutrient solution, attempt to wash excess from soil with heavy leaching.

Magnesium (Mg)—mobile (essential)

About: Cannabis uses a lot of magnesium. It is the central atom in every chlorophyll molecule, and it is essential to the absorption of light energy and photosynthesis. It aids in the utilization of nutrients. Magnesium helps enzymes make carbohydrates and sugars that are later transformed into flowers. It also neutralizes the soil acids and toxic compounds produced by the plant. 

Deficiency: Deficiencies are common indoors and occasionally outdoors, especially in acidic soils. No deficiency symptoms are visible during the first 3 to 4 weeks. In the fourth to sixth week of growth, the first signs of deficiency appear. Interveinal yellowing and irregular rust-brown spots appear on older and middle-aged leaves and younger leaves remain healthy. Size of rust-brown spots between green veins increases and migrates to lower and finally newer leaves as the deficiency progresses. The entire plant looks sick. Rusty-brown spots appear on the leaf margins, tips, and between the veins. Leaves start dying and dropping, possibly curling before falling off. A minor deficiency will cause few problems with growth. However, minor deficiencies can quickly escalate during flowering and cause a diminished harvest as flowering progresses. 

A magnesium deficiency is easy to correct with applications of Epsom salts.

Cause: Magnesium is bound in the soil if there is an excess of potassium, ammonia (nitrogen), and calcium (carbonate). Most often, magnesium is in the soil but unavailable to the plant because the root environment is too acidic, wet and cold. Clay soils rich in calcium also tend to be magnesium poor. Small root systems are also unable to take in enough magnesium to supply heavy demand. A high EC slows water evaporation and diminishes magnesium availability.

Confused with: An excess of potassium, ammoniacal nitrogen, and calcium carbonate Spray with a 2 percent solution of Epsom salts every 4 to 5 days. 

Solution: Add superfine dolomite lime to acidic potting soils before planting; it will stabilize the pH and add magnesium and calcium to the growing medium. Add 2 teaspoons (10 cc) of Epsom salts (magnesium sulfate) per gallon (3.8 L) of water with each watering to correct magnesium deficiencies if no dolomite was added when planting. Or dilute Kieserite (magnesium sulfate monohydrate, MgSO4·H2O) in water. For fast results spray the foliage with a 2 percent solution of Epsom salts every 4 to 5 days. If the deficiency progresses to the top of the plant, it will turn green there first. In 4 to 6 days, the green-up will start moving down the plant, turning lower leaves progressively greener. Continue a regular watering schedule with Epsom salts until the symptoms totally disappear. Use Epsom salts designed specifically for plants rather than the supermarket type. Another option is to apply Kiese-rite, found packaged as Ca-Mg fertilizer/ supplement. Composted cow and turkey manure is also rich in magnesium.

Control room and root-zone temperatures, humidity, pH, and EC of the nutrient solution. Keep root zone and nutrient solution at 70°F to 75°F (21.1°C–23.9°C). Keep ambient air temperature at 75°F (21.1°C) day and 65°F (18.3°C) night. Use a complete fertilizer with an adequate amount of magnesium. Keep the soil pH above 6.5, the hydroponic pH above 5.5, and reduce high EC for a week. Reduce EC by leaching with plain water.

Excess: Excess magnesium is rare and does not appear quickly. Extra magnesium in the soil is in itself generally not harmful, but it inhibits calcium uptake. Symptoms appear as an overall salt toxicity accompanied by stunted growth and dark-green foliage.

Cause: Magnesium toxicity is rare and difficult to discern with the naked eye. If extremely toxic, the magnesium develops a conflict with other fertilizer ions, usually calcium, especially in hydroponic nutrient solutions. Toxic buildup of magnesium is uncommon in soil that is able to grow cannabis. 

Confused with: Calcium deficiency

Solution: Leach soil heavily to wash out excess.

Sulfur (S)—semimobile (essential)

About: Sulfur is an essential building block of many proteins, hormones, and vitamins, including vitamin B1. Sulfur is also an indispensable element in many plant cells and seeds. The sulfate form of sulfur buffers the water pH. Virtually all groundwater and river or lake water contains sulfate. Sulfate is involved in protein synthesis and is part of cysteine (an amino acid) and thiamine, which are building blocks of proteins. Sulfur is essential in the formation of oils and flavors, as well as for respiration and the synthesis and breakdown of fatty acids.

Deficiency: Sulfur is not commonly deficient; many fertilizers contain some form of it. Excess sulfur is somewhat common when the EC is high. Young leaves turn lime-green to yellowish, and growth is stunted. As shortage progress­es, leaf veins yellow and lack succulence. Leaf tips can burn, darken, and hook downward. Roots also elongate and stems often turn woody. Acute defi­ciency is usually caused by a rising pH resulting in a loss of phosphorus, which in turn causes more and more leaves to turn yellow and leaf stems to turn purple. Long purple streaks might appear the length of the stem when combined with an overall nutrient deficiency. Buds may have difficulty forming, often remaining leafy and fluffy, with reduced potency. Bud formation is slow and weak. Plants could have shorter overall life.

Mauk from Canna in the Netherlands, who has conducted detailed scientific ex­periments with nutrients, says, “We have repeatedly noticed that the symptoms were most obvious in the older leaves. Sulfur deficiency resembles a nitrogen deficiency. Acute sulfur deficiency causes elongated stems that become woody at the base.”

Sulfur is abundant in most fertilizers; when deficient it is usually mixed with other nutri­ents. Low sulfur levels cause buds to be fluffy and less potent.

Cause: Sulfur deficiency occurs indoors when the pH is too high (above 6.0) or when there is excessive calcium present and available. Hydroponic fertilizers separate sulfur from calcium in an “A” container and a “B” container. If com­bined in a concentrated form, sulfur and calcium will form crude, insoluble gyp­sum (hydrated calcium sulfate) and settle as residue to the bottom of the tank.

Confused with: Nitrogen, magnesium, iron deficiencies.

Solution: Fertilize with a hydroponic fertilizer that contains sulfur. Balance the pH to 5.5 in hydroponics and above 6.0 in soil gardens. Add inorganic sulfur to a fertilizer that contains magnesium sulfate (Epsom salts). Organic sources of sulfur include mushroom composts and most animal manures. (To avoid burning the roots, make sure to apply only well-rotted manures.) Avoid ele­mental (pure) sulfur in favor of sulfur compounds such as magnesium sulfate. The nutrients combined with sulfur mix better in water.

Excess: Seldom seen or a problem except in coco mediums that are already rich in sulfur. Excess sulfur symptoms include overall smaller plant development and uniformly smaller, dark-green foliage. Leaf tips and margins could discolor and burn when excess is severe.

Cause: An excess of sulfur in the soil causes no problems if the EC is relatively low. At a high EC, plants tend to take up more available sulfur, which blocks uptake of other nutrients.

Confused with: Potassium and manga­nese deficiencies.

Solution: Leach the growing medium of affected plants with a very mild and complete fertilizer. Check the pH of the drainage solution. Correct the input pH to 6.0. Severe problems require more water to be leached through the growing medium. Leach a minimum of 3 times the volume of water for the volume of the growing medium. Lower the overall fertilizer concentration (EC) of nutrient solution.


Micronutrients, also called trace ele­ments or trace nutrients, are essential to cannabis growth and must be present in minute amounts. They function mainly as catalysts to the plant’s process and utilization of other elements.

Organic fertilizers such as marine algae or kelp (liquid or meal), humic acid, manures, and composts often contain all necessary micronutrients.

To ensure that a complete range of trace elements is available, use ionic salt fertilizers (designed for hydroponics) that supply all necessary micronutrients in proper proportions. High-quality hydroponic fertilizers use food-grade ingredients that are completely soluble and leave no residues.

Due to labeling requirements, many fertilizer companies do not list trace elements that are actually contained in their products. Before adding chelated trace elements, check with manufacturers to see if it is a “complete” fertilizer with all necessary nutrients.

Chelated micronutrients are available in powdered and liquid form. Add and thoroughly mix micronutrients into the growing medium before planting. Micronutrients are often impregnated in commercial potting soils and soilless mixes. Check the ingredients on the bag to ensure that the trace elements were added to the mix. Trace elements are necessary in minute amounts but can easily reach toxic levels. Follow manu­facturer’s instructions when applying mi­cronutrients; they are easy to overapply.

Zinc, iron, and manganese are the three most common micronutrients found deficient. Often deficiencies of all three occur concurrently, especially when the soil or water pH is above 6.5. Deficien­cies are most common in arid climates— such as Spain, the southwestern United States, and Australia—with alkaline soil and water. All three have the same initial symptom of deficiency: interveinal chlo­rosis of young leaves. It is often difficult to distinguish which element—zinc, iron, or manganese—is deficient, and all three could be deficient. This is why treating the problem should include add­ing a chelated dose of all three nutrients. Remember that chelation technology is expensive and really only required when mediums are alkaline.

Read your fertilizer’s ingredients— chelated iron might read something like “iron EDTA.”


A chelate (Greek for claw) is an organic molecule that forms a clawlike bond with free electrically charged metal particles, combining nutrients in an atomic ring that is released easily for plants to absorb only at the root surface. Plants do not take up a chelate directly. First, the metal is converted in an ionic form at the root surface. There, ions are released and absorbed by the plant, where it is re-chelated and moves through the plant. This property keeps metal ions such as zinc, iron, and manganese soluble in water, and the chelated metal’s reactions with other materials is suppressed. Roots take in the metals in a stable, soluble form that is used immediately.

Natural chelates such as humic acid and citric acid can be added to organic soil mixes. Roots and bacteria also secrete natural chelates (exudates) in order to promote the uptake of iron and other metallic elements. Man-made chelates are designed for use in different situations. Chelators may move back to the growing medium to pick up another metal, but supporting evidence for this is marginal.

DTPA is most effective in a pH < 6.5.
EDDHA is effective up to a pH < 8.0.
EDTA chelate is slow to cause leaf burn.

Chelates decompose rapidly in low levels of ultraviolet (UV) light, including light produced by HID bulbs and sunlight. Keep chelates out of the light to protect them from rapid decomposition.

This information was condensed from Canna Products,

Boron (B)—very immobile

About: Boron is still somewhat of a biochemical mystery. We know that boron helps with calcium uptake and numerous plant functions and is critical for photosynthate transfer. Scientists have collected evidence to suggest that boron helps with synthesis, a base for the formation of nucleic acid (RNA uracil) formation. Strong evidence also supports boron’s role in cell division, differentiation, maturation, and respiration as well as a link to pollen germination.

Deficiency: Cannabis uses minute amounts of boron, and deficiencies seldom occur indoors. Usually boron causes no problems, but it must be available during the entire life of a plant. Stem tip and root tip grow abnormally if it is deficient. Root tips often swell, discolor, and stop elongating. Growing shoots look burned, which may be con­fused with a burn from being too close to the light. First, leaves thicken and become brittle, and then top shoots con­tort or turn dark (or both), which is later followed by progressively lower-growing shoots. When severe, growing tips die, and leaf margins discolor and die back in places. Necrotic spots develop between leaf veins. Root steles (insides) often become mushy—perfect hosts for rot and disease. Deficient leaves become thick, distorted, and wilted, with chlorotic and necrotic spotting. Rust-colored cork tissue forms on stems, and growing tips have a witch’s broom appearance. Boron deficiency often brings about calcium deficiency.

Cause: Not present in extremely poor soil or lacking in fertilizer.

Confused with: Calcium deficiency and light burn (See photos of each to distinguish.)

Solution: Give boron-deficient plants one teaspoon (5 cc) of boric acid or borax soap per gallon (3.8 L) of water. You can apply this solution as a soil drench to be taken up by the roots, or apply hydroponic micronutrients containing boron. Hydroponic gardeners should keep boron dosage below 20 parts per million (ppm), because boron quickly becomes toxic if it is concentrated in the solution.

Excess: Excesses are rare but can be deadly. Older leaves are affected first and symptoms are similar to salt burn. Leaf tips yellow first, and as the toxic conditions progress, leaf margins become necrotic toward the center of the leaf. After the leaves yellow, they fall off. Be careful when adding trace elements to soil and hydroponic nutrient formula­tions. Avoid using excessive amounts of boric-acid-based insecticides.

Cause: Overfertilization.

Confused with: Leaf spot fungus, light burn.

Solution: Difficult to correct an over­supply of boron before crop is mature.

Chlorine (Chloride) (Cl)—immobile (essential)

About: Chlorine (chloride) is required in the molecule that holds the water molecule, allowing and triggering the breakdown and release of hydrogen and oxygen for photosynthesis to occur. It is necessary for root and leaf cell division. It also increases osmotic pressure in the cells, which opens and closes the stomata to regulate moisture flow within the plant tissue. Chlorine is found in many municipal water systems. Cannabis tolerates low levels of chlorine and is almost never deficient in gardens that grow cannabis. Excess chlorine is some-what common indoors. Chlorine tends to acidify soil after repeated applications. 

Deficiency: Chlorine deficiency is rare. A solution concentration of less than 140 ppm is usually safe for cannabis, but some varieties may show sensitivity when new and young foliage turns pale green and wilts. Excessive chlorine causes leaf tips and margins to burn and causes the leaves to turn a bronze color. The roots develop thick tips and become stunted. 

Note: Both severe deficiency and excess of chloride have the same symptoms: bronze-colored leaves. 

Cause: Not available in water or soil.

Confused with: Chlorine excess. 

Solution: Add chlorinated water.

Excess: Young leaves develop burned leaf tips and margins. Young seedlings and clones are the most susceptible to damage. Later, the symptoms progress throughout the plant. Characteristic yellowish-bronze leaves are smaller and slower to develop. Most grow well with chlorine levels up to 140 ppm, but some varieties develop leaf tip and margin burn when concentrations top 20 ppm.

Note: Both severe deficiency and excess of chlorine have the same symptoms: bronze-colored leaves. 

Cause: Too much chlorine in the home or municipal water system.

Solution: Let heavily chlorinated water sit out overnight, stirring occasionally, or aerate it with a pump. Chlorine will volatize and disappear into the atmosphere in 24 to 48 hours. Place an air pump or a water pump and fountain in the chlorine-rich water to speed volatization of chlorine. Use this water to mix the nutrient solution or to irrigate the garden. If chlorine noticeably alters water pH, adjust it with a commercial pH UP product. Correct soil excesses by adding fine dolomite or agricultural lime.

Water treated with chlorine dioxide can be dealt with in this fashion, but water systems that use chloramine cannot, as it does not volatize; reverse osmosis is required, or a chemical purifier could be used, but the latter is not necessarily recommended.

Simple water filters do not clean dissolved solids from water. Such filters remove only debris emulsified (suspended) in water, releasing dissolved solids from their chemical bond isomer complex. A reverse osmosis machine uses small polymer, semipermeable membranes that allow pure water to pass through yet filter out dissolved solids. Reverse osmosis machines are the easiest and most efficient means to clean raw water.

Confused with: An excess of iron evidenced by bronze-colored leaves.

Cobalt (Co)—immobile (beneficial)

About: Cobalt is necessary for nitrogen fixation, although the need for cobalt in plants was only recently established. It is essential for growth of the bacteria Rhizobium involved in legume nodule formation and fixing atmospheric nitrogen into amino acids and proteins.

Cobalt, found in vitamin B12, is synthesized by Rhizobium to promote nitrogen fixation. Cobalt slows ethylene synthesis. Ethylene, a hormone, inhibits new shoot development. More new shoot development is possible when ethylene is inhibited. It is still not clear as to other direct influences cobalt might have on cannabis growth.

Deficiency: Nothing is known yet of symptoms, etc. Possible symptoms might include decreased production of Vitamin B12 and less nitrogen fixation.

Copper (Cu)—semimobile (essential)

About: Copper is a component of numerous enzymes and proteins. Necessary in minute amounts, copper helps with carbohydrate metabolism, nitrogen fixation, and the process of oxygen reduction. It also helps with the making of proteins and sugars. Copper is also used as a fungicide.

Deficiency: Copper is used in minute amounts by cannabis. Deficiencies are uncommon indoors or outdoors. Young leaves and growing shoots slowly wilt, twisting and turning under in the process. Leaf tips and margins develop necrosis and turn dark-green to copper-gray. Occasionally, an entire copper-deficient plant wilts, drooping even when adequately watered. Growth is slow and the yield decreases. A small deficiency can cause new shoots to die back. Flowers are retarded and fail to mature properly. 

Cause: Lack of copper in fertilizer and growing medium. Copper is concentrated in roots.

Confused/mixed with: possible boron deficiency or a pathogen attack (insect, virus, etc.)

Solution: Apply a copper-based fungicide such as copper sulfate. To avoid burning foliage, do not apply if the temperature is above 75°F (23.9°C). Apply a complete hydroponic nutrient that contains chelated copper. Or apply chelated trace elements containing copper. Be careful not to overapply.

Excess: Excess copper is somewhat common indoors but seldom seen outdoors. Copper, although essential, is extremely toxic to the plant even in minor excess. Toxic levels slow the overall plant growth. As the toxic level climbs, symptoms include interveinal iron chlorosis (deficiency) and stunted growth. Fewer branches grow, and roots start to decay, or become thick and slow growing. Toxic conditions accelerate quickly in acidic soils. Hydroponic gardeners must carefully monitor their solution to avoid copper excess.

Cause: Too much copper in fertilizer, copper built up in soil to toxic levels, or residue accumulated on foliage or in soil from copper-based fungicides.

Confused with: Iron deficiency demonstrated by interveinal chlorosis.

Solution: Leach the soil or the growing medium to help expel excess copper. Do not use copper-based fungicides or foliar sprays.

Iron (Fe)—semimobile (essential)

About: Iron is fundamental to the enzyme systems and to transport electrons during photosynthesis, respiration, and chlorophyll production. Iron permits plants to use the energy provided by sugar. A catalyst for chlorophyll production, iron is necessary for nitrate and sulfate reduction and assimilation. Iron colors the earth from brown to red, according to concentration. Most soils contain plenty of iron in different forms. But cannabis often has a difficult time absorbing it under many conditions. Soil pH is a major factor dictating absorption of iron. Acidic soils normally contain adequate available iron for cannabis growth. 

Deficiency: Iron deficiencies are most common when pH is above 6.5 and un-common when the pH is below 6.5 in soil and 6.0 in hydroponic gardens. Symptoms may appear during rapid growth or stressful times and may disappear by themselves. Mild iron deficiencies have little effect on harvest. Young leaves are unable to draw immobile iron from older leaves, even though it is present in the soil. The first deficiency symptoms appear on young leaves and shoots as veins remain mostly green and areas in between turn yellow. Interveinal chloro-sis starts at the opposite end of the leaf tip: the apex of the leaves attached by the petiole. As the deficiency progresses more and larger leaves demonstrate interveinal chlorosis. Large leaves may yellow completely. In acute cases, leaves may develop necrosis and drop. Medium to severe iron deficiencies inhibit growth and diminish harvest. Do not confuse with magnesium deficiency where interveinal chlorosis shows on older leaves first.

Iron deficiencies are somewhat common. The sativa plants on the left are deficient in iron; the afghani plants on the right are not. (MF)

Cause: Imbalanced pH, especially above 6.5 in soil and 6.0 in hydroponics. Manganese, zinc, and copper inhibit iron uptake. Overwatering, poor drainage, cold growing medium, and damaged or rotten roots will all lower iron uptake. Nutrient solution exposed to light causes algae growth. Algae break down chelates and robs iron from roots. Sterilizing the nutrient solution with UV light causes iron to precipitate. 

Confused with: Magnesium deficiency; nitrogen deficiency; and early stages of copper, manganese, and zinc deficiencies. In contrast to magnesium, iron deficiency appears first in younger leaves because of iron’s relative immobility. Iron readily oxidizes to the Fe3+ ion and precipitates out in the tissues of the plant, including the phloem.

Solution: Lower the soil pH to 6.5 or less; rockwool and hydroponic substrates require about 5.6 to 5.8. Avoid fertilizers that contain excessive amounts of phosphorus, manganese, zinc, and copper, which inhibit iron up-take. High levels of phosphorus compete with the uptake of iron. Improve the drainage; excessively wet soil holds little oxygen to spur iron uptake. Increase root zone temperature. Foliar feed for guaranteed results with dilute EDDTA 0.2 teaspoons per quart (0.1 gm/L) or EDTA at half a teaspoon per quart (0.5 gm/L). Apply 5 to 10 times the recommended dose of chelated iron in liquid form to root zone. Chelates are decomposed by light and must be thoroughly mixed with the growing medium to be effective. Leaves should green up in 4 or 5 days. Complete and balanced nutrient formulas contain iron, and deficiencies are seldom a problem. Organic sources of iron, as well as chelates, include cow, horse, and chicken manure. (To avoid burning cannabis plants, use only well-rotted manures.) Remember that foliar application of chelated iron is only a temporary fix. 

Caution: If iron deficiency is pronounced, add only chelated iron to remedy the problem. Iron often reacts with other nutrients, causing them to become unavailable.

Excess: Excess of iron is extremely rare except in flooded soils. High levels of iron do not damage cannabis but can interfere with phosphorus uptake. An excess of iron causes leaves to turn bronze, accompanied by small, dark-brown leaf spots. Iron excess can also promote phosphorus deficiencies. 

Cause: Flooded outdoor soils where iron accumulates.

Confused with: Phosphorus deficiency.

Solution: Leach plants heavily. Avoid deficiencies by using a high-quality hydroponic fertilizer that contains chelated micronutrients.

Manganese (Mn)—immobile (essential)

About: Manganese is engaged in the oxidation-reduction process associated with photosynthetic electron transport. This element activates many enzymes and plays a fundamental part in the chloroplast membrane system. Manganese assists nitrogen utilization along with iron in chlorophyll production.

Deficiency: Manganese deficiency is relatively uncommon indoors and relatively uncommon outdoors. Young leaves show symptoms first, becoming yellow between veins (interveinal chlorosis) while veins remain green. Symptoms spread from younger to older leaves as the deficiency progresses. Necrotic (dead) spots develop on severely affected leaves, which become pale and fall off; overall plant growth is stunted, and maturation may be prolonged. A telltale sign of manganese deficiency is where margins remain dark green surrounding interveinal chlorosis. 

Cause: A high pH (above 6.5) or an excess of iron causes manganese deficiency. Lack of manganese in the soil or fertilize.

Confused with: Severe manganese deficiency looks similar to magnesium deficiency.

Solution: Lower the pH, leach the soil, and add a complete, chelated micronutrient formula.

Excess: Problems with manganese excess are somewhat common. Young and newer growth develops chlorotic, dark orange to dark rusty-brown mottling on the leaves. Tissue damage shows on young leaves before progressing to older leaves. Growth is slower, and overall vigor is lost.

Cause: Toxicity is compounded by low humidity. The additional transpiration causes more manganese to be drawn into the foliage. A low pH (5.0–5.5) can cause toxic intake of manganese, which in turn restricts intake of iron and zinc.

Confused with: Excess of iron and zinc Solution: Raise pH to 6.5.

Molybdenum (Mb)—mobile (essential)

About: Molybdenum is part of two major enzyme systems that convert nitrate to ammonium. This essential element is used by cannabis in very small quantities. It is most active in roots and seeds. 

Deficiency: Molybdenum deficiencies and excesses are rare, though occasional deficiencies occur in cold weather. First, the older and middle-aged leaves yellow; some leaves develop interveinal chlorosis and discolor around leaf edges. Leaves continue to yellow and develop cupped or rolled-up margins as the deficiency progresses. Leaves become distorted and twisted, dry along the edges die, and then drop. Overall growth is stunted. Deficiencies are worst in acidic soils. Molybdenum deficiency promotes nitrogen shortage. 

Molybdenum deficiency

Cause: Not present in fertilizer, growing medium, or water.

Confused with: Nitrogen deficiency.

Solution: Water with chelated micro-nutrients that contain molybdenum. Be careful not to overapply.

Excess: Excess molybdenum is uncommon in cannabis gardens; it is difficult to detect and has little effect on cannabis. Leaves discolor. An excess of molybdenum causes a deficiency of copper and iron.

Cause: Too much in soil or fertilizer

Confused with: Copper and iron deficiency.

Solution: No correction needed.

Nickel (Ni)—mobile (beneficial)

About: Nickel was first demonstrated as an essential plant nutrient in 2004. Cannabis requires nickel in trace amounts. It is normally not listed on fertilizer labels because nickel is available in soil. Nickel is essential for activation of the enzyme urease, which helps metabolize (urea) nitrogen. It is also required for absorption of iron. Nickel also has a function in bacteria, and it may play a role with interaction between plants and bacteria. At a pH less than 6.7 nickel is moderately available, but at a pH less than 6.5 nickel compounds are very soluble.

Deficiency: A lack of nickel causes toxic levels of (urea) nitrogen to accumulate, causing dead lesions to form on foliage. Excessive application of zinc, copper, or magnesium could cause a deficiency. But cannabis requires so little nickel that I have never seen a case where it is deficient. Plants grown without additional nickel will gradually reach a deficient level at about the time they mature and begin reproductive growth. If nickel is deficient, plants may fail to produce viable seeds.

Cause: Excessive zinc, copper, manganese, iron, calcium, or magnesium in soil or by root-knot nematode damage.

Confused with: Nitrogen (urea), zinc, copper, or magnesium excess.

Solution: Apply copper, zinc and magnesium in trace amounts to fertilizers so that they do not build up to toxic levels. Nickel-deficient soils have not been identified

Excess: A nickel overload is virtually never a problem unless gross quantities are available in soil. Cannabis as an accu-mulator plant can absorb a lot of nickel. 

Cause: Overdose can be caused by too much nickel in soil or by soil fertilized with sewage sludge or packed with heavy metals from industrial pollution. 

Confused with: Does not apply.

Solution: Grow in soil that is not full of industrial waste or sewage sludge packed with heavy metals.

Selenium (Se)—semimobile (beneficial)

About: Not yet classified as an essential nutrient for plants, selenium’s role as a beneficial element for plants is still being discovered. Some plants are able to accumulate large amounts of selenium, from 100 to 10,000 mg Se kg-1 dry weight. However, little work has been done regarding cannabis as a selenium accumulator plant. Selenium can be absorbed by roots in an inorganic source or via organic compounds. Sulfur and selenium share close chemical and physical qualities and their absorption by roots is also similar.

Deficiency: Selenium is seldom if ever deficient. No apparent symptoms.

Cause: No selenium in growing medium.

Confused with: No deficiency.

Solution: No action.

Silicon – (Si)—immobile (beneficial)

About: Silicon deserves mention even though I have never seen a diagnosed deficiency. Low levels of silicon can reduce overall yield and vigor of cannabis. Only rushes require silicon to complete their life cycle, but it is beneficial in other plants and accumulates in the endoplasmic reticulum, cell walls, and intercellular spaces as hydrated, amorphous silica. Silicon is found in all soils and it is the only nutrient/element that does not hurt cannabis in excess. Silica (gel) accumulates in epidermal plant cells to form a protective shield that promote stronger leaves, roots, stems, and resistance to diseases, pests, and plant stresses (including drought). 

Silica (not silicon) is a mineral sand; hydrated amorphous silica SiO2-H2O is what Si is deposited as in the intercellular spaces, converted after take-up. 

Deficiency: Lodging (falling over) and fungal infections. 

Cause: Silicon deficiency is usually only seen in plants not grown on native or natural soils, or plants grown in water. 

Confused with: Nothing Solution: Add silicon to fertilizer in the form of diatomaceous earth or prepackaged supplements. When applied in a highly soluble form, added silicon takes effect after two weeks or more.

Note: Pests and diseases have a difficult time penetrating plants that are sprayed with a silicon-based repellent/insecticide.

Excess: Evidence suggests that too much silicon can be an issue, but little research has been done.

Sodium – (Na)—mobile

At low levels, sodium appears to bolster yields, possibly acting as a partial substitute to compensate for potassium deficiencies. But in excess of 50 ppm, sodium is toxic and induces deficiencies of other nutrients, primarily potassium, calcium, and magnesium.

About: Very low levels of sodium appear to promote higher yields in cannabis. 

Deficiency: Not a problem in C3 plants like Cannabis.

High levels of sodium in tap water will block nutrient uptake and stunt growth.

Cause: Not a problem.

Confused with: Nothing.

Solution: No action.

Excess: Sodium excess (above 50 ppm) is relatively common, especially in coastal and rural zones. Sodium in excess is a big problem. Small amounts of sodium are quickly taken up by roots. When sodium levels reach 50 ppm, potassium and other nutrient uptake is blocked, resulting in rapid and severe deficiencies. First signs of toxic sodium levels in plants manifest as a potassium deficiency. When mixed with chlorine, sodium turns into table salt (NaCl), which is the worst possible salt to put on plants.

Sodium excess causes potassium deficiency, which in turn causes the internal temperature of foliage to climb and protein cells to burn or degrade.

Evaporation is normally highest on leaf edges, which burn. See Potassium above for more information.

Cause: Overall toxic fertilizer salt condition in growing medium, salts in water from water-softening filters, or sodium in water or soil. Using too much baking soda as a fungicide can also create an excess.

Confused with: Potassium, calcium, or magnesium deficiencies.

Solution: Leach growing medium heavily with clean water to wash away toxic sodium. Use reverse osmosis filtration to remove sodium and other dissolved solids from irrigation water.

Note: Use a sodium (Na) meter to check for salt content in all premixed and bulk soils—especially those containing manure fertilizers.

Vanadium Vanadium is known to be required in certain microbes and algae, but nothing is known about its need in higher plant forms. Some believe it might be required by cannabis in very low concentrations.

Zinc (Zn)—immobile (essential)

About: Zinc works with manganese and magnesium to promote the same enzyme functions. Zinc cooperates with other elements to help form chlorophyll as well as prevent its demise. It is an essential catalyst for most plants’ enzymes and auxins, and it is crucial for stem growth. Zinc plays a vital part in sugar and protein production. It is fairly common to find zinc-deficient cannabis. Deficiencies are most common in soils with a pH of 7.0 or more.

Deficiency: Zinc is the most common micronutrient deficiency and is commonly found in arid climates and alkaline soils. The most dynamic evidence of zinc deficiency is when a leaf turns 90 degrees and is combined with some or all of the following symptoms: New and young leaves exhibit interveinal chlorosis, and new leaves and growing tips devel-op small, thin blades that contort and wrinkle. Some varieties grow pronounced smaller leaves. The leaf tips, and later the margins, discolor and burn. Burned spots on the leaves could grow progressively larger. When zinc deficiency is severe, new leaf blades contort horizontally and dry out. Often stem tips fail to elongate and growing shoots/tips become “bunched up.” Flower buds also contort into odd shapes, turn crispy dry, and are often hard. A lack of zinc causes reduces internode spacing, stunts new growth— including buds—and can severely diminish yield.

This Colombian bud grown in 1976 is deficient in zinc. The result is bunched-up and contorted growth. (MF

A zinc deficiency on the ‘Pakistani’ (lower left) is easy to remedy with an application of fritted trace elements (FTE). (MF)

Cause: The pH is too high (above 7.0), which in turn causes iron, manganese, and zinc deficiencies to occur together.

Confused with: Symptoms are often confused with a lack of manganese and iron.

Solution: Treat zinc-deficient plants by leaching the growing medium with a diluted mix of a complete fertilizer containing chelated trace elements, including zinc, iron, and manganese. Or add a quality-brand hydroponic micro-nutrient mix containing chelated trace elements. Foliar feed if problem is severe.

Be careful; do not overapply chelated micronutrients.

Excess: Zinc overload is very rare but extremely toxic. Severely toxic plants die quickly. Excess zinc interferes with iron’s ability to function properly and causes an iron deficiency.

Cause: Oversupply in fertilizer.

Confused with: Iron deficiency.

Solution: Leach growing medium with a diluted mix of a complete fertilizer.


The selection of fertilizers at hydroponic and cannabis-friendly garden stores can be overwhelming. Local shop personnel generally know which ones work best in the local climate and water. Local hydroponic store staff are often well versed on local water and gardeners’ needs. 

Nutrients in a fertilizer formula can be classified as inorganic, mineral, natural, organic, and synthetic. Inorganic nutrients have no carbon molecules, mineral elements are inorganic salts; organic substances are animal or vegetable in origin and contain a carbon molecule; synthetic materials are man-made. But mineral elements such as dolomite lime, rock phosphate, and Epsom salts are considered organic. All these terms can be very confusing, and they are often misused! 

The main difference between organic fertilizer and mineral fertilizer formulas is the way in which they are taken up by plants. In general, organic fertilizers (mineral and natural) require biological life in the soil to break down components and make nutrients available to roots for uptake. Mineral fertilizers (inorganic and synthetic) are taken up by plants exclusively via ionic activity, a chemical bond formed by the attraction of positive and negative soluble ionic fertilizer salts. Virtually all elements, regardless of origin, must be broken down into a single element in order to pass into a cell of a root. Single ionic elements react faster and are easier to control. Of course, the science is much more complex than this simplified expla-nation. The aim of this book is to give you a basic understanding of fertilizers, so you can efficiently grow a healthy crop of medical cannabis. 

Ionic fertilizer salts are separated into two or three different containers so they can be mixed together in a concentrate form and not combine into an insoluble compound. For example, when calcium and sulfur are combined in a concentrated form, they combine into an insoluble compound. This compound (calcium sulfate) settles to the bottom of hydroponic tanks in the form of an insoluble compound (sludge). They may flocculate (form aggregates) or not, depending on agitation. They combine to form an insoluble compound that you may see as crystal growth (flocculation) at the bottom of the tank. Vegetative and flowering formulas are further separated into different containers. Nutrients are available for uptake by plant roots within a specific pH range.

In hydroponic gardens this range is from 5.5 to 6.5, and in organic soil gardens the range is a little higher, 6.0 to 6.8. Maintaining a relatively constant pH is essential to nutrient uptake. A common oversight among novice enthusiasts is to forget about pH. For example, iron and manganese deficiencies are rampant when pH climbs beyond 7.0 in hydroponic gardens. No matter how much of each element is in the nutrient solution, they will become available only at a lower pH.

The big buds on these plants were grown in Morocco with the aid of little fertilizer.

Canna Vega and Aqua formulas are just a few of the many different fertilizers available at hydroponic stores.

This beautiful field of organically grown cannabis belonged to Eddy Lepp, who is currently serving a 10-year sentence for cultivating cannabis.

Fertilizers mixed in liquid concentrate form are very convenient to use but are more expensive both in monetary terms and to the environment. Nutrients available in a dry form are much more economical than nutrients mixed with water. Dry fertilizers are also much more eco-friendly because no water/fertilizer concentrate, which is expensive, must be transported. Dry fertilizers are not separated because the elements do not react with one another. Purchase dry fertilizers or concentrated liquid fertilizers that dilute readily in water.

Fertilizers are either water-soluble or partially soluble (gradual-release). Both soluble and gradual-release fertilizers can be organic or chemical. Soluble salt (ionic) fertilizers dissolve in water and are simple to measure and control; they can easily be added or washed (leached) out of the growing medium. 

Chemical granular fertilizers work well for perennial shrubs and trees but can easily be overapplied on annual cannabis. Long-lasting granular fertilizers are very difficult to leach out of soil. 

Osmocote chemical fertilizers are time-release and are used by many nurseries because they are easy to apply and only require one application every few months. Using this type of fertilizer may be convenient, but exacting control is lost. They are temperature- and moisture-dependent, with release rates calculated at 70°F (21°C) and normal ir-rigation. I have seen three-month formulations release in total during a month with high soil temps. Also, they release somewhere between 30 percent and 70 percent the first time water is applied. They are best suited for ornamental containerized plants or perennial plants growing in soil, where labor costs and uniform growth are the main concerns.

Use hydroponic fertilizers designed to supply plants with a specific diet that includes all necessary nutrients at the proper ratio required for strong growth. These formulas must be applied on a regular schedule to achieve the best results. Precisely formulated fertilizers allow much easier dosage control dosage by altering the EC. Less-precise fertilizers provide plants more nutrients than they need and let roots absorb what they need. These formulations tend to build up in growing mediums. Subsequently, plants often suffer an excess of nitrogen or other nutrients that are “overapplied” when the mix is changed and flowering is induced.

Apply the proper nutrient combination at the appropriate stage of life. For example, cannabis absorbs more phosphorus and potassium for a short time early on in the flowering stage. Applying more fertilizer earlier or later causes it to build up in soil, sometimes to toxic levels. 

1. Ratio for N-P-K fertilizer: start: 2-1-1, veg.: 1-1-1, finish 1-2-2*

2. great site! 

3. *Remember that, by convention, P and K are confusing on the label, while 1-1-1 is correct, the percentage given on the label for P is only 40 percent of actual P, and K is only 80 percent of actual K. 

Do not combine fertilizers from different manufacturers. Each manufacturer designs formulas to function with products in their line. Mixing and matching brands could easily lead to deficiencies or excesses.

Take care when including additives in fertilizer mixes. Use additives designed for specific fertilizers and mix them according to the fertilizer schedule. These products are designed to stimulate specific nutrients and plant process. Adding too much or too little—or at the wrong time—could be futile or even toxic.

Fertilizer is big business, and convenience is expensive. Manufacturers often sell “special mixes” that contain just a few of the necessary nutrients. Be wary when purchasing high-priced specialized fertilizers that are broken down into four or more “essential” products. The “formulas” often include only one or two different nutrients that could easily be combined into a single product and sold for less. In the end, the goal of such fertilizer companies is to sell a thimbleful of salts mixed in a bottle of water— at astronomical profits.

In the United States, nutrients are measured in parts-per-million (ppm), even though they are expressed as a percentage concentration on the label. The ppm scale is simple and finite—well, almost. The basics are simple: one ppm is one part of 1,000,000. To convert from percentage to ppm, multiply by 10,000 and move the decimal four spaces to the right. For example: 2 percent equals 20,000 ppm. For more information on ppm and electrical conductivity, see chapter 23, Container Culture & Hydroponics

Osmocote time-release fertilizer is perfect for fuchsias and other perennial plants, but it is not a good fertilizer to control a medical cannabis crop grown in containers.

Irrigation hoses with tubing supply a daily dose of properly proportioned nutrient solution to this greenhouse full of plants.

This big plant grown on a patio in downtown Barcelona, Spain, was given a simple fertilizer

Organic Fertilizers

Patients prefer cannabis that is grown organically because it has a sweeter taste, but contrary to popular belief, organically grown cannabis does contain salts. Fertilizer salts are ions; ions are released by the breakdown of organic molecules, which is the only way a plant will take them up, so salts are there, but the levels are lower. Implementing an organic garden outdoors, in a greenhouse, or indoors usually requires a large mass of rich organic soil with good drainage. Space is limited indoors, so growing with a large mass of living organic soil is impractical for most indoor gardeners.

Most indoor organic gardens use potting soil high in worm castings, peat, sand, manure, leaf mold, compost, and fine dolomite lime. In a small container, there is little space to build nutrient-rich soil by mixing compost and organic nutrients that interact. Fill containers with rich organic potting soil that is ready to release nutrients. Add a liquid mix of nutrients periodically if necessary. 

Biological activity also takes months of valuable growing time, and it could foster destructive diseases and pests. Tossing out used and depleted soil and then recycling it in the outdoor garden keeps indoor and greenhouse gardens clean.

This organic fertilizer lists N, P, and K on the label, showing the chemical composition of each nutrient. At the base of the package is a list of what the nutrients were derived from.

This fertilizer contains N, K2O, Ca, B, Fe (EDTA), and Mo, which are the major and minor nutrients consumed by cannabis. The mix lacks P, S, Mg, and Z, which are supplied in other products. The nutrients are provided in a readily available form for uptake by roots.

Most countries have an agency that certifies organic materials for gardening. This bale of Canadian peat moss is certified by the Organic Materials Review Institute (OMRI).

Always read fertilizer labels carefully. Follow mixing and application instructions. Pay special attention to the expiration date, especially on organic nutrient packages. They often contain living organisms that will die or change composition over time. Make sure all necessary nutrients are listed on the label. For example, Miracle-Gro does not contain magnesium!

Miracle-Gro plant food is available everywhere. It is a favorite fertilizer for many flower and vegetable gardeners. The Guaranteed Analysis shows it contains N, P, K, Mn, and Zn. It is derived from urea, potassium chloride, potassium, phosphate, manganese EDTA, and zinc EDTA. But, medical cannabis gardeners prefer a more complete fertilizer that has a complete range of all necessary nutrients.

Note the “derived from” part of the label. Using potassium and magnesium carbonate derivatives can cause the pH to climb. If a high pH brings about phosphorus and iron deficiencies, add chelated iron to remedy and to avoid precipitation as well.

Fertilizers must be registered so they can be regulated by governments to ensure content, and protect consumers from illegitimate companies that make false claims. Even when regulated, companies still make false claims not found on labels. The “guaranteed analysis” of nutrients on labels guarantees minimums of specific elements. It does not guarantee that more of these specific elements are in the container. Often lower-quality fertilizers contain other elements as impurities that are not included on the label. All “organic” products should be certified by an independent third party such as the Organic Materials Review Institute (OMRI, in North America and the Control Union ( in Europe. There are many other organic certification organizations around the world, including, Organic Crop Improvement Association (OCIA, Check with these organizations for added information on products that are not allowed.

When using synthetic fertilizers, it is extremely important to carefully read the label and follow the directions. The initials “WSN” and “WIN” that you may see on the label stand for water-soluble nitrogen and water-insoluble nitrogen. WSN dissolves readily, and it is considered a fast-release nitrogen source. WIN does not dissolve easily. It is often an organic form of nitrogen and is considered a slow-release nitrogen source.

Bio-Canna is one of the many different organic fertilizers available to medical cannabis gardeners.

Chicken manure has long been a favorite organic fertilizer for outdoor and greenhouse gardens. It is packed with nitrogen and other soluble nutrients to spur rapid growth.

This raised bed is in a suburban backyard garden in California, a medical cannabis state.

Raised beds and very large (50–500-gal [189.3–1892.7 L]) containers with good drainage allow organic soil life to grow in indoor, greenhouse, and outdoor gardens. The raised beds and large containers have enough soil to hold the nutrients, promote soil life, and when managed properly, ensure an available supply of nutrients. There must be enough mass to support healthy soil life. Outdoor organic gardens are much easier to implement and maintain. Using compost tea, manures, compost, and other big, bulky, fragrant fertilizers is much easier outdoors. Gardeners in Northern California are using rich organic soil mixes to grow big plants, 10 pounds (4.5 kg) plus, with the local nutrient-rich soil mixes, adding about 2 handfuls of bat guano when plants start to flower.

Cannabis plants grow from 2 to 6 months in containers indoors and in greenhouses. Start with rich organic soil and add (soluble) liquid organic nutrients to ensure rapid plant growth. Liquid organic nutrients are often more expensive to manufacture than ionic salt fertilizers. Nutrient-rich organic soil is expensive to build and usually both inexpensive and trouble-free to maintain.*

*Often organic cannabis gardeners get carried away and add too many microbes on a regular basis. Uninformed product producers and retailers may also promote such practices. Consequently microbes are rampantly available, to a fault. 

Soil microbes are not all created equal. There are both specific and general decomposers and these different species or types work at differing levels in the soil. Nutrients form what are collectively known as ‘pools’ (freely available elements locked onto cation exchange capacity (CEC) sites or drifting in the soil solution) in the medium, such as nitrogen or calcium pools, etc. As organic material decomposes, it adds to these pools when there is more released than is used by the microbes. When mineral fertilizer is used, these same pools collect these elements. The elements are collected in pools over time rather than all at once. Microbes are very much like vacuums and will suck it up faster than plants and will outcompete plants for these elements. Balance in these microbes is essential so the pools stay in place. 

For example, a large amount of organic soil starts the breakdown with specific microbes, and what they release is broken down by the next type, and so on until it is gone. (For more specific information, check out the book Teaming with Microbes by Jeff Lowenfels and Wayne Lewis). When all these general populations of microbes multiply to greater than the available organic material for decomposition, these microbes dip into the pools and outcompete the plants in order to stay alive. Most commercially available microbes are largely made up of general decomposers, and are opportunistic feeders that will eat (take up) anything that is available.

Big pots 2 feet (61 cm) tall and 4 to 6 feet (121.9–182.9 cm) across function like raised beds. They capture extra heat in the spring and carry it through fall. The containers must be shaded if they get too hot in summer.

Growing large plants in small containers requires more work. The substrate must receive regular irrigation with nutrient solution and be kept within a good temperature range. These plants have received excellent care!

Large plants are growing in 2 × 2-foot (61 × 61 cm) planting holes and the surround ing soil is hard clay. Good organic fertilizer and plenty of water helped these plants grow up to 6 feet (182.9 cm) tall.

Big issues arise when organic cannabis gardeners apply microbes above and beyond the need (uneducated manufac-turers may provide this erroneous information). In turn these microbes take up and use nutrients before the plants can. Proper organic garden maintenance requires constantly supplying new organic matter for all the microbes to enjoy—but not the wrong ones that the nutrient balance.

The organic nutrient content, solubility, and rate of release are characteristically lower than ionic salt-based fertilizer. Organic fertilizers are more dilute and less readily available to plants. They can change slightly from one batch to another. Testing each batch is necessary to ensure consistent nutrient levels.

Outdoors, organic gardening is easy because all the forces of nature are there for you to seek out and harness. When playing the role of Mother Nature, you must create everything in the environment.

Start with good soil that drains well, and add proper organic nutrients. Organic fertilizers improve soil life and the long-term productivity of soil. Increase soil organisms by providing organic matter and micronutrients to soil life, which aids plants in absorbing nutrients and can drastically reduce pesticides, fertilizer, and energy use, at the cost of decreased yield. Organic fertilizers usually require the use of microbes/ bacteria in the soil in order to make the nutrients in the fertilizer bioavailable. That can result in irregular release of phosphorus/calcium. In sterile potting soil, there may be no microbes to release the nutrients.

Note: Nutrients in organic fertilizers may vary greatly depending upon source, age, erosion, and climate. For more precise nutrient content, consult the vendor’s specifications. Make sure composts are well-rotted and do not contain pathogens and other disease-causing organisms.

Some commercial liquid organic fertilizers contain living organisms— microbes, bacteria, fungi, etc.—and tend to grow under certain conditions. Do not leave containers of organic fertilizers in warm places. And remember to use them before their expiration date! Check labels closely; some companies add preservatives to their mixes. 

Organic nutrients (manure, worm castings, blood and bone meal, and so forth) work very well to increase the soil nutrient content, but nutrients are released and available at different rates. The nutrient availability may be tricky to calculate, but it is somewhat difficult to overapply organic fertilizers. Organic nutrients are typically more consistently available when used in combination with one another. Usually, gardeners use a mix of up to 20 percent worm castings with other organic agents to get a strong, readily available nitrogen base.

Organic fertilizers include ground-up and rendered animal and fish products, bird and bat guanos, animal manures, fish, shellfish, kelp, seaweed, rock powders, vegetable meals and extracts, plus coffee grounds, compost and compost teas, ashes, and worm castings. See the “Organic Nutrient List” for information about specific organic nutrients. 

The selection of commercial fertilizers designed specifically for hydroponics and cannabis growth is often overwhelming to gardeners.

Worm castings supply readily available nitrogen and many other nutrients in an organically available form. Add potent worm castings, and mix well in substrates. They are dense and tend to clump.

available phosphoric acid (P2O5)0.2
soluble potash (K2O)18
sulfur (S)8
copper (Cu)0.05
iron (Fe)0.7
zinc (Zn)0.2

Brix Mix

Brix Mix Powder is used by many Northern California cannabis gardeners.

The mix is formulated to increase Brix (sugar content) in plants. The mix is derived from Ascophyllum nodosum kelp, sulfate of potash, iron lignosulfonate, zinc lignosulfonate, copper lignosulfonate.

Dry Brix Mix contains ratios of Maxicrop, Diamond K sulfate of potash, sugar, and available trace minerals. Brix liquid contains Phytamin 4-3-4, Humax humic acids, pure malt extract, molasses, sulfur, and Therm X70 Yucca Extract.

Mixing Fertilizers

To mix wettable powder or crystal fertilizers, dissolve into a little warm water. Mix the super concentrate until all powder or crystals have dissolved. Once it has totally dissolved, add the balance of the tepid water. This will ensure that the fertilizer and the water mix evenly. Liquid fertilizers can be mixed directly with water. Always agitate fertilizers before pouring from the container, and keep nutrient solution in tanks agitated.

Unless fortified, soilless mixes require fertilization from the start. I like to start fertilizing fortified soilless mixes after the first week or two of growth. Most commercial soilless mixes are fortified with trace elements.

Mix organic fertilizer components dry. Sprinkle a mist of water overhead to dampen dust. Mix components thoroughly before wetting. Mix large amounts in an electric cement mixer that can be rented for the day. Mix small amounts in a barrel, wheelbarrow, or corner of a basement.

Always use an accurate measuring container.

These plants in Dennis Peron’s* backyard in San Francisco, California, receive full sun and quite a bit of wind all day long. The pots get too hot and growth is slowed. *Dennis Peron is coauthor of California Proposition 215, which enacted the first law in the USA allowing patients to purchase cannabis for medicine at dispensaries.

Fertilizer Application

The goal of fertilizing is to supply plants with proper amounts of nutrients for vigorous growth, without creating toxic conditions by overfertilizing. Some varieties of cannabis can withstand high doses of nutrients, and other varieties grow best with a minimum of supple-mental fertilizer. Every medicinal cannabis variety requires specific fertilizer applications. A blanket application of fertilizer for all varieties is impossible to give. Growing several different varieties in a small garden is common but can lead to underfertilization of some varieties and overfertilization of others.

The metabolism of cannabis changes as it grows and so do its fertilizer needs. During germination and seedling growth, intake of phosphorus is high. The vegetative growth stage requires larger amounts of nitrogen for green-leaf growth, and phosphorus and potassium are also necessary in substantial levels. 

During this leafy and vegetative growth stage, use a general purpose or a grow fertilizer with high nitrogen content. In the flowering stage, nitrogen is still necessary, but potassium and phosphorus intake increases so the N-P-K ratio changes. Using a super bloom fertilizer with less nitrogen and more potassium, phosphorus, and calcium promotes fat, heavy, dense flower buds. Cannabis still needs nitrogen during flowering. With no nitrogen, buds do not develop to their full potential. 

A 3-gallon (11.4 L) container full of rich, fertile organic potting soil should supply all the necessary nutrients for the first month of growth, but plant development might be slow. After the roots have absorbed most of the available nutrients, more must be added or become available organically to sustain vigorous growth. Medical cannabis growing in small containers will have very little growing medium in which to hold nutrients, and toxic salt buildup may become a problem. Follow fertilizer dosage instructions on the label. Search cannabis cultivation forums for more information on specific fertilizer mixing and application. Adding too much fertilizer will not make the plants grow faster. Too much fertilizer changes the chemical balance of the soil, supplies too much of a nutrient, or locks in other nutrients, making them unavailable to the plant. 

Caution! Do not pour nutrients down household drains—or any drain. The nitrates, phosphates, and other contents will pollute the water supply. Use them outdoors in the garden. 

A measuring cup, a measuring spoon, and a funnel are essential to measure and handle accurate doses of nutrients when mixing.

FloraGro and FloraBloom from General Hydroponics are popular hydroponic fertilizers

Plants use more nitrogen during the vegetative growth stage. These healthy plants require a spherical trellis to hold up rapid vegetative growth.

Fertilizer/Irrigation Schedule

A regular fertilizing schedule with realistic outcome and known input is the easiest way to ensure that plants receive all the nutrition they need. When choosing a fertilizer, also choose the proper substrate the formula was designed for. Many fertilizer programs are augmented with different additives that expedite nutrient uptake. 

If the fertilization schedule does not work, and you have discerned that plant growth is out of whack, check for the following outward signs of nutrient deficiencies.

Determine if the plants need to be fertilized: Make a visual inspection, take an N-P-K soil test, or experiment on test plants. No matter which method is used, remember, plants in small containers use available nutrients quickly and need frequent fertilizing, while plants in large planters have more soil, supply more nutrients, and can go longer between fertilizing. 

Visual Inspection: If the plants are growing well and have deep-green, healthy leaves, they are probably getting all necessary nutrients. The moment growth slows or the leaves begin to turn pale green, it is time to fertilize. Do not confuse yellow leaves caused by a lack of light with yellow leaves caused by a nutrient deficiency. Leaves should be green all the way to the bottom of the plant. But by the time the plant tells you there is an issue, it is too late.

Nutrient solution is delivered at regular inter­vals via the overhead irrigation tube.

With a little practice it is easy to eyeball plants and tell what they need. The leaf on the right is properly fertilized. The pale plant on the left looks like it is deficient in nitrogen.

This lovely medical cannabis gardener grew this giant bud in a pot on a patio in Spain. Regular irrigation and fertilization were her keys to gardening success.

The fact is that the relationship between nutrient uptake and plant growth is very subtle. By the time a nutrient deficiency manifests with a discolored leaf or slow growth, the dysfunction has already slowed growth. 

To get an idea of which cannabis varieties need a little or a lot of fertilizer, I asked members of my forum on To learn the best way to fertilize specific varieties, you may need to contact the company that sold you the seeds. Start with an EC of 1.6 and build it up as needed. The absolute maximum EC is 2.3. 

This healthy, properly fertilized plant is growing as fast as naturally possible.

A basic EC meter can tell you if nutrients have built up to toxic salt levels.

An overall toxic buildup of nutrients is easy to spot in most plants. You can see that these leaves are too dark and shiny. The plant in the center is so overfertilized that leaves have turned dark purple, with the veins remaining green.

Varieties that require high doses of fertilizer: 
Overall indica-dominant clones root well, with the possible exception of ‘Hindu Kush’ (a landrace, with less vigor and not as nutrient-hungry as hybrid indicas). In this case, ‘more fertilizer’ means using the high end of the recom-mended dosage, not exceeding it.

A few of the varieties that in general can withstand higher doses of fertilizer include: ‘Twilight’, ‘Green Spirit’, ‘Khola’, ‘Hollands Hope’, ‘Passion#1’, ‘Shaman’ within an EC range of 1.6–2.3.

Varieties that require medium doses of fertilizer: 
Many varieties require a standard dose of fertilizer including the varieties below. ‘Skunk #1’, ‘Trance’, ‘Voodoo’, ‘Sacra Frasca’, ‘California Orange’, ‘Delta 9’, ‘Skunk Passion’, ‘Blueberry’, ‘Durban Poison’, ‘Purple #1’, ‘Purple Star’, ‘ Super Haze’, ‘Ultra Skunk’, ‘Orange Bud’, ‘White Widow’, ‘Power Plant’, and ‘Euforia’

Varieties that require low doses of fertilizer: 
Overall, sativa-dominant varieties and hybrids require much less fertilization. There are exceptions, including ‘Silver Pearl’, ‘Marley’s Collie’, and ‘Fruity Juice’ (sativa hybrids, but with a heavy, indica-dominant bud pattern). In this case, less fertilizer means using the low end of the recommended dosage. ‘Northern Lights #5 x Haze’ has more open buds in its growth pattern but a lot of floral bulk by weight, so may need normal to slightly higher levels of nutrient.

‘Isis’, ‘Flo’, ‘Dolce Vita’, ‘Dreamweaver’, ‘Master Kush’, ‘Oasis’, ‘Skywalker’ and ‘Hempstar’ are within an EC range of 1.6 to 2.3. ‘Mazar’ needs a higher EC during weeks three to five to prevent early yellowing of the leaves.

Take an EC test of runoff water to tell how much nutrient is trapped in the soil. Make a batch of 0.1 EC nutrient solution. Drench plants in containers with one gallon (3.8 L) of solution. Check the EC of the runoff water. If it is above 0.1 EC, there is a toxic buildup of nutrients in the soil. The soil needs to be leached with a mild nutrient solution to purge it of toxic fertilizer salts. 

Take an N-P-K soil test to reveal exactly how much of each major nutrient is available to the plant. Test kits mix a soil sample with a chemical. After the soil settles, a color reading is taken from the liquid and matched to a color chart. The appropriate percent of fertilizer is then added. This method is reliable but requires patience. But this test does not measure the amount of each nutrient that plants are actually processing.

Indoors, regular fertilizer application is essential to ensure rapid growth.

Outdoors, plants can take in virtually all the necessary nutrients from specially mixed soil.

Experimenting on two or three test plants is the best way to gain experience and develop horticultural skills. Start with a fertilization schedule and amend it as needed according to temperature, humidity, and growth stage. Clones (cuttings) are perfect for this type of experiment. A basic premise is to give the test plants a fertilizer schedule and see if they grow better and faster. You should notice a change within three to four days. If it is good for the test plants, it should be good for all plants of the same varieties.

How much fertilizer? Mix the fertilizer as per the instructions and water as normal, or dilute the fertilizer and apply it more often. Many liquid fertilizers are diluted already. Consider using more concentrated fertilizers whenever possible. Remember, small plants use much less fertilizer than large ones. Fertilize early in the day so plants have all day to absorb and process the fertilizer and water. Watering late in the day or at night can lead to waterlogged roots. 

Fertilizer programs rely upon soil or substrate drainage. Frequency of irrigation also depends upon drainage. Large plants with a large root system in large containers use more nutrients than small plants in small containers. But small containers must be irrigated more often. The more often the fertilizer is applied, the less concentrated it should be. Frequency of fertilization and dosage are both affected by substrate drainage ability.

The concept in fertilizing is to either apply fertilizer periodically or constantly. Periodic includes dry and liquid fertilizers and is applied at higher ranges (dosages) to get the plant through the use period until the next application. This results in too high a concentration for the first half of the period and too low for the second half. Weekly applications, for example, begin with an ideal range the plant needs to satisfy exactly its requirements. Let’s say that this particular plant needs a root zone EC of 1.0 for exactly the right amount of all nutrients to be available. We feed on Monday to bring the level to 1.6, and by the next feeding 7 days later the EC is at 0.4. For 3.5 days the EC is too high and the plant has small issues, from day 4 to day 7 the level is below the ideal level of 1.0 for 3 days as it drops to 0.4 and the plant development also slows. Then feed is again applied, and the plant restarts until the next lag.

The second version is constant feeding. This applies an EC of 1.1 each watering, and by the next watering the EC has fallen to just under 0.9. Then the lag is fixed within a day or a day and a half. The plant never notices and growth goes unabated. All commercial Green Industry producers use constant feeding because the plant is never overfertilized, nor is it ever really underfed. Salt levels remain balanced and the plants do remarkably better.

A pre-fertilized peat-based mix usually has enough calcium and possibly other elements. Coco absorbs large quantities of calcium at the beginning of the growing cycle. Fertilizer schedules need to have this and other details built in to support a successful crop. Choose a substrate and a fertilizer designed for it. 

Some varieties can absorb amazing amounts of fertilizer and still grow well. Lots of gardeners add as much as one tablespoon per gallon (14.8 ml per 3.8 L) of a standard dry soluble fertilizer such as Peters (20-20-20) with each watering. This works best with growing mediums that drain readily and are easy to leach. Other gardeners use only rich, organic potting soil. No supplemental fertilizer is applied until a super bloom formula is needed for flowering.

Fertilizing plants in the ground outdoors is much easier than fertilizing containerized plants. In healthy, outdoor organic soil, nutrient uptake is rapid and buffered, and fertilization is not as critical. There are several ways to apply fertilizer. Top-dress a garden bed by applying the fertilizer and working it into the top 2 inches (5.1 cm) of soil. Apply a dilute liquid fertilizer around the bases of plants. Foliar-feed plants by spraying a liquid fertilizer solution on the foliage. The method you choose will depend upon the kind of fertilizer, the needs of the plants, and the convenience of a chosen method.

Use a siphon (venture pump) applicator—found at most nurseries—to mix soluble fertilizers with water. The applicator is simply attached to the faucet with the siphon submerged in the concentrated fertilizer solution with the hose attached to the other end. Often, applicators are set at a ratio of 1 to 15. This means that for every single (1) unit of liquid concentrate fertilizer, 15 units of water will be mixed with it. Sufficient water flow is necessary for the suction to work properly. Misting nozzles restrict this flow. When the water is turned on, the fertilizer is siphoned into the system and flows out the hose. The fertilizer is generally applied with each watering, since a small percentage of fertilizer is metered in.

Containers full of soilless growing medium are set on top of Canna Coco slabs in this top-feed hydroponic garden.

This medical cannabis gardener brings in truckloads of compost and manure. Once in place she uses a tractor to cultivate it into the soil before planting.

Leaves curl when given a slight fertilizer overdose.

Injector Applicator

A Dosatron fertilizer injection sys-tem makes it easy to feed a big indoor, outdoor or greenhouse garden with a consistent pH-balanced fertilizer mix. Fertilizer injectors range in price from $250 to $800 USD depending upon volume injected. Injectors can also meter out pH up and pH down, fungicides, pesticides, etc. When using fertilizer injectors, make sure the nutrient concentrate is completely mixed with water before application in drip emitters.

A garbage can with a garden-hose fitting attached at the bottom that is set 3 to 4 feet (91.4–121.9 cm) off the floor will act as a gravity-flow source for the fertilizer solution. Place the reservoir on the floor of the next level of the house to increase water pressure. The container is then filled with water and fertilizer. Set containers up on a table to gain pressure and flow. 

When it comes to fertilization, experi-ence with specific varieties and growing systems will tell gardeners more than anything else. There are hundreds of N-P-K mixes, and they all work, some better than others. When choosing a fertilizer, make sure to read the entire label, and know what the fertilizer claims it can do. Do not be afraid to ask the garden store clerk questions or to contact the manufacturer with questions. Cannabis cultivation forums also help gardeners share their experiences with fertilization of specific varieties. 

Once you decide how often to fertilize, put the garden on a regular feeding schedule. Following a schedule usually works very well, but it must be combined with a vigilant, caring eye that looks for overfertilization and signs of nutrient deficiency.

Leach soil with 1 to 2 gallons (3.8–7.6 L) of mild nutrient solution per gallon of soil every month to prevent toxic salt buildup in the soil. Mix the EC 0.2 in soil and peat, 0.5 in coco; Epsom salts are good for soil and peat, but use only nutrients for coco.

Stomata close when there is: 
too much CO2 
low humidity 
a dry root system 

Stomata open when there is: 
high light 
low CO2 
high humidity 

Dosatron fertilizer injection systems are becoming more popular.

Foliar Feeding

Foliar feeding means to spray nutrients or additives diluted in water onto plant foliage. Foliar sprays can provide a “quick fix” for some nutrient deficiencies. This feeding method is best employed when damaged and stressed roots are not working properly. Some sources claim foliar feeding speeds rooting time of clones (cuttings) when applied sparingly. Easy to overdo, foliar feeding can leach nutrients, especially when plants are young or have few or no roots. 

Making complete or general recommendations on foliar feeding is impossible because we do not know everything. Scientists believe that most of the nutrients and stimulants stay in the location they enter unless specifically designed by Mother Nature to translocate, which means that the rest of the plant will not benefit from foliar feeding.

We know that nitrogen (N) and iron (Fe) translocate well, but phosphorus (P) does not move well within the plant because of its ion size. Using dimethyl sulfoxide (DMSO) or another carrier helps every-thing move but is also harmful for the consumer, especially medical patients!

Some commercial products, such as Canna’s Boost, can be applied as a foliar spray every 3 days but mineral fertilizer should not be applied nearly so often. Furthermore, accumulating nutrient residues will burn plant tissue if they are not taken up. Complex organic molecules seldom burn plant tissue or cause problems.

Not all elements are able to translocate across the outer skin (epidermis) of foliage. The waxy (cuticle) surface coating (cystolith hairs and resin) on cannabis foliage makes for very poor water absorption. This barrier wards off pest and disease attacks, but it also slows the penetration of sprays.

Young, supple leaves are more permeable than older leaves. Nutrients and additives penetrate immature leaves faster than tougher, older leaves, and they are easier to damage with strong sprays. 

Spraying foliage underneath so the spray is able to penetrate the stomata located on the leaf’s underside does not work. Experts seem to agree that application to the stomatal areas is no more effective than application to the leaf surface, because the structure of the stomata will seldom allow intrusion by the liquid.

Plants properly maintained hardly, if ever, need foliar feeding. The roots are designed by Mother Nature for nutrient uptake and are still be best means of supplying nutrition. Do not foliar feed flowering plants; moisture trapped in between foliage increases probability of disease. 

Foliar feeding should be used only as a supplement. Never spray more than once every 7 to 10 days, if at all, and keep the spray concentration at quarterstrength.

Foliar feeding is a quick fix for some nutrient deficiencies.

Leaves and stalks have waxy, cystolith hairs that act like feathers on a duck to shed water. See chapter 24, Diseases & Pests, for information on spraying.

Always calibrate thermometers and hygrometers to ensure their accuracy.

Adequate ventilation is essential in greenhouses and in indoor garden rooms.

Common “Nutrient” Problems

To help avoid common Problems: 
1. Use proper, complete nutrient 
2. Do not overwater 
3. Control pH and EC 
4. Leach soil once a month 

There is a short list of common problems that often result in nutrient deficiencies and excesses. Unhealthy plants grow slowly, produce poorly, and are susceptible to attacks by pests and diseases. Controlling the critical cultural factors that cannabis needs to grow will help avoid nutrient imbalances. Nutrient imbalances are usually a result of incorrect cultural essentials—air, light, water, growing medium, and nutrient solution. Each of these factors, along with pH and EC, will affect nutrient uptake. When the basic needs of plants are not met, controlling pH and EC will have minimal effect on nutrient uptake.

Nutrient deficiencies are less common when using fresh potting soil fortified with micronutrients, or a hydroponic mix containing all necessary elements. If the soil or water supply is acidic, add dolomite lime to buffer the soil pH and to keep it sweet. Evaluate all factors in enclosed garden rooms and greenhouses, especially temperature and ventilation, before deciding that plants are nutrient deficient. 

Overall, plants in indoor gardens start to show outward stress signs in the sixth to eighth week of growth. Once a plant shows symptoms, it has already under-gone severe nutritional stress for one or two weeks. It will take time for the plant to stabilize and demonstrate vigorous growth. To help plants retain vigor, cor-rect identification of each symptom—as soon as it occurs—is essential. Indoor, greenhouse, and some outdoor cannabis crops are harvested so fast that plants do not have time to recover from nutrient imbalances. One small imbalance could cost a week of growth. That could be more than 10 percent of the plant’s life. In short, incorrect pH is reflected in stunted growth and lower harvest weight. 


Temperature: Both low and high temperatures slow the growth of plants. Large fluctuations in temperature— more than 15 to 20 degrees Fahrenheit (8 to 10 degrees Celsius)—cause slow growth by slowing the plants’ processes, including nutrient uptake. 

Solution: Lower the temperature by removing as many heat sources from the garden room as possible, or with venti-lation or air conditioning indoors. Vent greenhouses, cover them with reflective shade cloth, and install evaporative cooling. Outdoors, install shade cloth above plants. Raise temperatures indoors and in greenhouses by using a heater. Insulate garden rooms and install a heat blanket over greenhouses. Outdoors, cover plants with plastic to raise the temperature.

Humidity: High humidity causes stomata to open wide but slows evaporation, thus reducing water and nutrient movement. Low humidity increases water and nutrient movement, bringing too much to the plant. Low humidity stresses plants because they use too much water and higher nutrient levels.

Solution: Lower the humidity with ventilation, air conditioning, or a dehumidifier in enclosed garden area. Increase humidity by lowering temperature to 70°F (21.1°C) or by placing a humidifier in the garden area. 

Carbon dioxide (CO2): Growth is stifled and slows rapidly when CO2 is lacking. Nutrient and water consumption slows too. The growing medium is often overwatered, causing soggy roots and growth stagnation.

Solution: Increase air circulation so that all leaves in the garden flutter a little. This will keep CO2 from stagnating around foliage. Remove dense lower foliage that receives no light. Vent out CO2-poor air. Install a CO2 generator or CO2 emitter to increase CO2 levels.

Ozone damage: See chapter 16, Air, for more information on ozone damage.

Solution: Stop using an ozone generator indoors and in greenhouses.

Indoor air pollution: This causes very difficult-to-solve plant problems. Always be aware of chemicals bleeding or vaporizing from pressboard and other building materials. Such pollution causes plant growth to slow to a crawl. Ozone damage could also affect plant growth.

Solution: Remove problem-causing pressboard. Before reinstalling the removed pressboard, wait 6 to 12 months so that harmful chemicals have stopped outgassing. Stop using ozone generators, and switch to carbon filters to clean exhaust air. 

Heat Stress

The temperature within the leaves can climb to an excess of 110°F (43.3°C). It happens easily because leaves store heat radiated by lamps and sunlight. At 110°F (43.3°C), the internal chemistry of a cannabis leaf is disrupted. The manufactured proteins are broken down and become unavailable to the plant. As the internal temperature of the leaves climbs, plants are forced to use and evaporate more water. About 70 percent of the plant’s energy is used in this process. 

Solution: Leach growing medium to wash out excess fertilizer salts. Increase irrigation frequency, and lower the atmospheric temperatures with ventilation or other means described above. High humidity not only causes plants to grow looser but also the florets or individual flowers* to develop looser so that more water evaporates; this is a survival response. Because they are loose, fewer florets (individual flowers) are produced and overall weight is reduced. *A bud is a group of flowers, known as an inflorescence, by botanical definition.

Solution: Lower humidity with ventilation, a dehumidifier, or an air conditioner that also dehumidifies.

Along with curled leaf fringes, big ridges between veins signify temperature stress. Leaf edges that curl up signify that leaves are trying to dissipate as much moisture as possible. Moisture stress could be caused by toxic salt buildup, lack of water in the growing medium, or high atmospheric temperatures.

Low light levels cause spindly growth and poor utilization of nutrients. If plants are crowded and have poor air circulation, pests and diseases are more apt to be a problem.

Heat stress causes loose buds.


Lack of light: Nutrients are used poorly, photosynthesis is slow, stems stretch, and growth is scrawny.

Solution: Increase light levels by moving lamp closer to canopy of garden. Bend leggy plants to lower their profile so more light reaches the entire plant. 

Too much light: Keep a 600-watt lamp 20 inches (50.8 cm) above plants.

Light burn: Burned foliage is susceptible to attack by pests and diseases.

Solution: Indoors, move light further away from plants. Harden-off outdoor plants before placing outdoors so foliage is not soft and prone to burn. 

250 W10 in.25 cm
400 W15.7 in.40 cm
600 W20 in.50 cm
1000 W32 in.80 cm

Light-burned plant was too close to the hot HID!


Water quality: Check water quality for excess sodium (more than 50 ppm), and excesses of other dissolved solids such as calcium and heavy metals. Check pH and composition of dissolved solids on a well water analysis or a water analysis from your water district. Compare water analysis to the label of the fertilizer you are using. Add up the total of each element on the fertilizer label and the water analysis to calculate the entire fertilizer dosage plants are receiving. 

Irrigation: If the growing medium and root mass are kept saturated with water for 20 minutes or longer, roots will not have adequate oxygen and will die (drown) and start rotting.

Any growing medium that drains well can be irrigated or washed (leached) as many times as you want, as long as the soil does not stay saturated (and thus contain no oxygen) for longer than 20 minutes at a time. 

Water completely, until a minimum of 20 percent drains from the bottom of the container. Irrigate so that drainage occurs within 20 minutes of starting. Then the 50 percent rule applies before the next watering. See chapter 20, Water, “50 Percent Watering Rule,” for more information about watering. 

pH and EC: Control pH to the desirable soil or hydroponic range. Wash nutrients from soil to lower dissolved salts in growing medium. 

Solution: Irrigate using reverse osmosis (RO) water with fertilizer added. RO water will guarantee that your fertilizer mix will be consistent and easy to control. Manage EC in hydroponic tanks by topping off tanks with water every few days. Change nutrient solution in reservoirs every 7 to 14 days. When running higher EC levels, irrigation frequency must be increased so that plants do not dry down.

A clean source of water is essential for a healthy garden. Always check the water for dissolved solids with an EC/ppm meter. This pond is full of algae that must be treated and filtered before use.

This containerized plant was weighed, dry, at 8.1 ounces (230 gm).

When saturated with water, the same containerized plant weighs 16.6 ounces (470 gm)

Catch runoff water from plants to measure EC and pH.

Growing Medium

To avoid most common nutrient deficiencies and excesses: 
1. Use new store-bought soil indoors and in the greenhouse 
2. Use well-composted, amended, or new store-bought soil outdoors 
3. Add 1 cup (23.7 cl) of dolomite lime to each cubic foot (28.3 L) of substrate to keep pH “sweet” or in the 6.0 to 7.0 range 
4. Measure all bulk soils that tend to change for sodium (Na)

Soil Temperature: Soil over 90°F (32.2°C) will harm the roots. Often, outdoor soil that is used in containers warms up to well over 100°F (37.8°C). I notice that my outdoor garden virtually stops growing when soil temperature reaches about 80°F (26.7°C).

Solution: Cool soil indoors and in greenhouses by lowering the temperature of the garden room and placing containers on concrete or cool floor, if possible. In any container garden, shade containers from light, paint them white to reflect light, and place reflective mulch on soil surface. Outdoors, mulch soil with at least 6 inches (15.2 cm) of straw, hay, or other vegetation, or use any mulch to cool the soil surface.

Roots receiving light: Roots turn green if light shines through the container or the hydroponic system. Roots require a dark environment. Their function slows substantially when they turn green. 

Solution: Indoors or out, paint containers an opaque color inside so roots stay in the dark. 

pH and EC: Keep both pH and EC at proper levels.

A good growing medium allows good drainage and holds plenty of moisture at the same time. This growing medium is packed with well-composted bark dust and woodchips. Dolomite lime has been added to stabilize pH.

Nutrient Solution

Nutrient balance: Change the nutrient solution in small systems regularly, every 7 to 14 days. This is the easiest way to keep recirculating solutions in balance and avert problems. The nutrient reservoir should also have a top to minimize evaporation and avoid the possibility of pollutants falling into the tank. Topping off the tank every day or two will compensate for water used by plants. Topping off will also keep the nutrient solution from concentrating.

Always use a complete hydroponic fertilizer that contains all necessary nutrients, including micronutrients in a chelated form. Do not use fertilizers designed for soil gardens in a hydroponic system. Use only fertilizers that list all necessary nutrients on the label.

Incorrect pH: Out-of-whack pH level contributes to most serious nutrient disorders in organic-soil gardens. Many complex biological processes occur between organic fertilizers and the soil during nutrient uptake. The pH can be decisive to the likelihood of these activities. Typically, a pH from 5.2 to 6.0 is acceptable for both vegetative and flowering growth. But a pH range of 5.6 to 6.0 for vegetative growth and 5.4 to 5.8 for flowering is best.

A low-pH, below 5.5, (acidic growing medium and nutrient solution) causes plants to become stunted and fail to reach their potential. A high pH also causes stunted growth, as well as a lack of iron and manganese. With a high pH, plants have very pale green leaves. Either way, adjusting the pH will solve the problem. 

Overfertilizing can become one of the biggest problems for indoor gardeners. Too much fertilizer causes a buildup of the nutrients (salts) to toxic levels, and it changes the soil chemistry. When overfertilized, plants’ growth is rapid and lush until toxic levels are reached. At this point, things become complicated. 

Chance of overfertilization is greater in a small amount of soil that can hold only a small amount of nutrients. A large pot or planter can safely hold much more soil and nutrients, but it will take longer to leach if fertilizer is overdone. It is very easy to add too much fertilizer to a small container. Large containers have good nutrient-holding ability.

Solution: To treat severely overfertilized plants, leach the soil with 2 gallons (7.6 L) of diluted nutrient solution per gallon (3.8 L) of soil to wash out all excess nutrients. The plant should start new growth and look better in one week. If the problem is severe and leaves are curled, the soil may need to be leached several times. After the plant appears to have leveled off to normal growth, apply the diluted fertilizer solution.

Check the nutrient solution’s pH and EC/ppm to ensure that they are in the safe range.

Always keep the pH meter calibrated properly with 7.0 and 4.0 reference solutions.

Dirty gardens promote pests and diseases.


Spray application damage: Some sprays are phytotoxic, others are very phytotoxic. They can burn foliage if the spray is too concentrated or if it is sprayed during the heat of the day.

Solution: Lower concentration of spray so that it is less phytotoxic. Spray plants early or late in the day when sunlight or artificial light is not shining directly on foliage. The spray should have a chance to dry on foliage before nightfall. Using clean water, wash spray off plants after 24 to 48 hours. 

Lazy Practices One lazy guy mixed Miracle-Gro into the central water system for his house so that he would not have to measure it out and apply. It was always in the water! 

A novice grower who purchased a popular fertilizer brand with “A” and “B” nutrients did not read the instructions. He made the error of applying small doses of “A” fertilizer until the bottle was finished. Next he applied “B” nutrient in doses. His crop was a ruin!

Organic Nutrients List

Animal-Based Fertilizer Meals 

Blood Meal Blood (dried or meal) is collected at slaughterhouses, dried, and ground into a powder or meal. It’s loaded with fast-acting soluble nitrogen (12 to 15 percent by weight), up to 1.2 percent phosphorus, and under 1 percent potash. The proteins are broken down quickly by soil life, and they become immediately available and will last up to 4 months. Blood meal is an ideal nitrogen source for heavy-feeding varieties or to green up a garden. Use as a topdressing and cultivate into soil, or apply up to 1 month before planting. Apply carefully because blood meal is “hot” and can easily burn foliage if overapplied. When blood meal is applied on top of the ground in a band around a garden, it will keep rabbits from eating too much of the crop. 

Blood meal

Bone Meal Bone meal* is an excellent natural source of phosphorus. It increases microbial activity and nutrient uptake to help phosphates become available to plants. The lime found in bones also lowers soil pH. Bone meal also contains calcium and some nitrogen and trace minerals. Finely ground bone meal becomes available more quickly than coarsely ground, and it is faster-acting in well-aerated soil. It is also an excellent supplement for transplants and to promote a strong, extensive root system. *Bone meal could transport Mad Cow Disease (bovine spongiform encephalop-athy). The outbreak of this disease was purportedly contracted by four humans in the UK who inhaled bone meal dust while spreading it in their gardens. Now most countries have changed processing standards and do not allow processing of diseased animals, which appears to have curtailed spreading of Mad Cow Disease via bone meal. No outbreaks have been reported in recent history.

Bone meal for gardening is available in two main forms: precipitated (unsteamed) and steamed. Avoid raw bone meal because lingering fatty acids slow decomposition. Most often, precipitate bone meal is used for animal feed, and steamed bone meal is used as fertilizer. When sold in animal feed stores, the percentage of phosphorus on precipitated products is shown instead of phosphate (P2O5). This means that 12 percent phosphate is equal to 27.5 percent phosphorus. To convert phosphorus to phosphate, multiply phosphorus by 2.29. For example, 12 percent phosphate × 2.29 = 27.5 percent phosphorus.

Bone meal

Precipitated (unsteamed) bone meal is made by grinding and dissolving bones in acid before bathing in lime solution. Calcium and phosphorous from bones bind together and precipitate out; they are extracted from the liquid and then dried. The very fine resulting particles contain 40 percent available phosphate but no nitrogen. The end product is dusty to work with. 

Steamed or cooked bone meal is made from fresh animal bones that have been boiled or steamed under pressure to render out fats that slow decomposition. The pressure treatment causes a little nitrogen loss and an increase in phosphorus. Steamed bones are easier to grind into a fine powder, and the process helps nutrients become available sooner. Steamed bone meal contains up to 30 percent phosphorus and about 1.5 percent nitrogen. The finer the bone meal is ground, the faster it becomes available to plants. Till it into soil at the rate of 10 pounds (4.5 kg) per 100 square feet (9.3 m2), or mix it into organic potting soil at the rate of one cup (236.6 cc) per cubic foot (28.3 L). Use as a topdressing and cultivate into soil, or apply up to one month before planting.

Feather Meal
Feather meal consists of feathers that are steamed under pressure, dried, and ground into a powdery feather meal. Feathers are dominated by the protein keratin. This protein occurs in hair, hooves, and horns and is broken down slowly by soil bacteria, making it a good long-term source of nitrogen. The nitrogen level ranges between 7 and 12 percent, depending upon rendering process. Often feathers are cooked with pressurized steam (hydrolysis) that pre-decomposes the meal. It is a good slow-release insoluble fertilizer and compost component that is available after four or more months. Feather meal is often mixed with poultry bedding, which speeds nutrient release. Mixing with bedding other than poultry will not hasten nutrient availability. Use as a supplemental source of nitrogen along with other fertilizers. Till into soil at the rate of 5 pounds (2.3 kg) per 100 square feet (9.3 m2), and add to compost piles and potting soil at the rate of 1 cup (236.6 cc) per 2 cubic feet (56.6 L). Feather meal is available online and sometimes at garden centers. 

Hoof and Horn Meal 
Hooves and horns collected from cattle at slaughterhouses are cooked, ground, and dehydrated to make this meal. Fineground horn meal makes slow-release nitrogen available a little faster. Soil bacteria must break down this slightly alkaline meal before it is available to the roots. Apply it a month before planting, and nitrogen will be available for up to 12 months afterward. It is a good compost activator and improves soil structure, too. This meal contains up to 12 percent nitrogen, 2 percent phosphorus, and no potassium. Use it as a supplemental source of nitrogen along with other fertilizers. Till into soil at the rate of 5 pounds (2.3 kg) per 100 square feet (9.3 m2) and add to compost piles and potting soil at the rate of 1 cup (236.6 cc) per 2 cubic feet (56.6 L). Available online and sometimes at garden centers, or it can be collected from pens for sheep and pigs.

Fish-Based Fertilizers

Fish Emulsion 
Fish emulsion, an inexpensive soluble liquid, is high in organic nitrogen, trace elements, and some phosphorus and potassium. This natural fertilizer is difficult to overapply, and it is immediately available to plants. Fish emulsion is available from 1 to 4 months after application. Inorganic potash is included in some formulas to add potassium to the fish emulsion. Odors from this product can cause real problems with animal pests. Even deodorized fish emulsion smells like dead fish. It contains up to 5 percent nitrogen, 2 percent phosphorus and 2 percent potassium. Apply as a diluted liquid fertilizer at the rate of 6 tablespoons (88.7 cc) per gallon (3.8 L) of water.

Note: Often, fish emulsion is processed after most of the proteins, enzymes, and nutrients have been rendered in previous processes. See “Fish Hydrolysate” below for a more completed fish fertilizer.

Fish emulsion

Fish Hydrolysate
Fish hydrolysate used as fertilizer is ground-up fish carcasses. It is not rendered nearly as much as fish used in emulsion products. Fish processing factories remove the meat for human consumption, and the rest—bones, cartilage, guts, and scales—are ground up and mixed with water. Enzymes are added to make the mix soluble. Higher-quality fish hydrolysate is ground more finely. Often bones and scales are separated, causing the mix to lack calcium, minerals and proteins. Oil is rendered from dried products cutting out much of the plant food.

Although more expensive, the highest quality liquid fish hydrolysate processes whole fish, digests them with enzymes before liquefying the product. The cold-processed offal putrefies rapidly and is stabilized with sulfuric acidic at a low pH. The process uses enzymedigested hydrolyzed liquid fish wastes instead of using heat and acids. This process retains more of the proteins, enzymes, vitamins and micronutrients than fish emulsions. Heated hydrolysate is moderately heated to render and concentrate oils into less complex plant food. Overheating can destroy numerous beneficial organisms. Carefully read product labels.

Fish hydrolysate contains up to 2 percent nitrogen, 4 percent phosphorus, and 1 percent potassium, as well as many proteins, vitamins, and micronutrients. It is often difficult to find at retail outlets but is available via online suppliers. Apply as a diluted liquid fertilizer at the rate of 6 tablespoons (88.7 cc) per gallon (3.8 L) of water.

Fish Meal 
Fish meal is made from dried fish or rendered fish carcasses that are heated and often treated with acid before being ground into a meal that is rich in nitrogen and trace elements. It contains up to 10 percent nitrogen that is available immediately and lasts up to four months. Some meals also contain phosphorus and potassium. Incorporate fish meal into soil mixes, cultivate it into soil as a fast-acting topdressing, or use as a compost activator. Unless deodorized, this meal can have an unpleasant odor that may linger indoors. Outdoors, control fish meal odors by cultivating it into the soil, covering it with mulch, and diluting (irrigating) after application. Always store it in an airtight container so it will not attract cats, dogs, or flies. Till into soil at the rate of 10 pounds. (4.5 kg) per 100 square feet (9.3 m2) or mix into organic potting soil at the rate of 1 cup (236.6 cc) per cubic foot (28.3 L). Use as a topdressing and cultivate into soil, or apply up to one month before planting.

Fish Powder 
Fish power is similar to meal and hydrolysate before processing. The source and treatment of fish dictates the quality of fish powder. It is dried with heat and turned into water-soluble powder. It is a high source of nitrogen, up to 12 per-cent, with a trace of potassium, 1 percent phosphorus, and many micronutrients. Hydrolysate powder also contains up to 5 percent potassium and 1 percent phosphorus. Most water-soluble fish powders can be mixed in solution and injected into an irrigation system. High-quality fish powders consist of dehydrated, pulverized whole fish. Some offer enzyme-treated hydrolyzed fish protein (see below) processed products. Make sure to read labels carefully before applying to plants! Till in 1 to 2 ounces per 100 square feet (9.3 m2), or mix 1 tablespoon (14.8 cc) per gallon (3.8 L) of water. 

Crab Wastes 
Crab wastes contain relatively high levels of phosphorus and calcium. Crab waste is ground and dried to stabilize decomposition. The location, diet, and species of crab will affect the meal content. Waste contains chitin, which promotes organisms that attack pest nematodes. 

Crab waste N-P-K runs about 5-2-0.5 and up to 10 percent calcium in this slow release fertilizer. Add crab waste 2 to 4 months before planting. Broadcast 10 pounds per 100 square feet (4.5 kg per 9.3 m2), and till into topsoil. Add to compost piles and mix into planting holes for seeds or transplants.


Bat Guano
Bat guano consists of the droppings and remains of bats. It is rich in soluble nitrogen, phosphorus, and trace elements. The limited supply of this fertilizer—known as the soluble organic super bloom— makes it expensive. Mined in sheltered caves, guano dries with minimal decomposition. Bat guano can be thousands of years old. Newer deposits contain higher levels of nitrogen and can burn foliage if applied too heavily. Older deposits are higher in phosphorus and make an excellent flowering fertilizer. Bat guano is usually powdery and is used any time of year as topdressing or diluted in a tea, also a great compost activator. Do not breathe the dust when handling it, be-cause it can cause nausea and irritation in the lungs. Guano superphosphate is also available. Water-soluble bat guano runs about 3-10-1 for N-P-K and is packed with growth-stimulating bacteria and microbes. Nutrients are available immediately for up to 4 months. Add before planting at the rate of 5 pounds per 100 square feet (2.3 kg per 9.3 m2). Add 3 teaspoons per gallon (14.8 ml per 3.8 L) of water and start fertilizing 1 to 2 weeks before flowering. Bat guano also functions as a mild fungicide when applied as a foliar spray. 

Seabird Guano
Seabird guano is high in nitrogen and other nutrients. The Humboldt Current, along the coast of Peru and northern Chile, keeps rain from falling, and decomposition of the guano is therefore minimal. South American guano is the world’s best and most accessible guano. The guano is scraped off rocks of arid ocean islands and is often mixed with seal droppings. Sea bird guano is also collected from many coastlines around the world, so its nutrient content varies. The average N-P-K of this soluble fertilizer is 10-3-1 is also packed with organic life. Apply before planting for nutrients that are available for more than four months. Till in 5 pounds per 100 square feet (2.3 kg per 9.3 m2) or as a tea at 3 teaspoons per gallon (14.8 ml per 3.8 L) of water, applied directly to the soil or made into a tea and applied as a foliar spray or injected into an irrigation system. Seabird guano also makes a good compost activator.

Bat guano fertilizer powder

Bat guano fertilizer liquid

Seabird guano


Manure and Bedding
Sometimes manures are collected, packaged, and sold pure. Most often, manures, each of which has specific biological, chemical, and physical characteristics, is packaged or collected with varying degrees of bedding—straw, sawdust, newspaper, chopped hemp fiber*, and cardboard. Livestock diet, weather, cleaning schedules, location, and so forth, dictate manure availability and consistency. Often manure can be delivered in bulk. At least 50 percent of the nitrogen and up to 70 percent of the potassium are found in urine mixed with manures and bedding. *HempFlax from The Netherlands produces very popular BioBase Bedding for livestock from hemp stalks. 

Manures are considered either “hot” or “cold.” Hot manures will burn plants, cold manures won’t. Poultry and swine manures, and fresh wet manures are “hot” and will burn plants. Most other manures are considered “cold” and seldom burn plants unless fresh. Well-composted manures do not burn plants or contain excessive salts. Fresh manures contain 60 to 70 percent more moisture than dry. Dried manures contain much higher levels of nutrients.

Cow and horse manure mixed with bedding make great additions to the compost pile and as an outdoor soil amendment. Swine manure is very wet and should be mixed with straw. Poultry manure also performs best when mixed with sawdust, straw, or other bedding.

But be careful: too much straw and sawdust bedding can use much of the available nitrogen and decrease yields.

Chicken (Poultry) Manure 
Chicken (poultry) manure is probably the richest single organic fertilizer in relation to available nitrogen, phosphorus, potassium, and trace elements. Purchase dry, composted chicken manure in bags for convenience, or buy it in bulk. Use it as a topdressing or mix it into soil before planting. Often chicken manure collected from farms is packed with decomposing feathers, which contain as much as 17 percent nitrogen; this is an added bonus. I used chicken manure in bulk and in bags. If you can find it locally at an organic chicken farm, it is the best! Make sure the chicken manure is composted for an extended period before use or it will burn anything because of the high uric acid content. Also weed seeds will be a giant problem.

The N-P-K runs low for chicken manure—about 1.5-1.5-0.5 wet, and 1.1- 0.8-0.5 dry—and it is packed with trace elements. Don’t let the low nutrient readings fool you; it is available immediately for up to 4 months. It can be heavy and bulky when wet, and bulky when dry. Add chicken manure up to a month before planting. Follow mixing instruc-tions found on the bag label.

Chicken manure

Cow Manure 
Cow manure is often sold as steer manure but is sometimes collected from dairy herds. Cannabis gardeners have used cow manure for centuries. It is a fair fertilizer and good soil amendment. Steer manure is most valuable as mulch and as a soil amendment. It holds water well and maintains fertility for a long time. The nutrient value is low, and it should not be relied upon for the main source of nitrogen. Let it compost for several months if salt content is high, which is often the case with feedlot cow manure. Washed dairy manure from healthy cows is an excellent soil amendment. The N-P-K runs very low—about 0.7-0.3-0.4—and it is full of trace elements. Add cow manure to soil a month or two before planting. Best used as a soil amendment and secondary fertilizer.

Cow manure

Goat Manure 
Goat manure is much like horse manure but more potent. The uniformly sized “nanny nuggets” are easy to “handle” and apply. They are most effective when broken up while incorporating with soil and compost. This manure increases soil’s water-holding ability and microbial activity, and does not attract flies or animals when dry or mixed with soil. Quality of the product depends upon goat feed. N-P-K runs about 1.3-1.5-0.5. Apply goat manure as an amendment or fertilizer.

Horse Manure 
Horse manure is readily available from horse stables and racetracks. Use horse manure that has straw, hemp straw, or peat for bedding. Wood shavings could be a source of plant disease. Compost fresh horse manure and bedding for two months or longer before adding it to the outdoor garden. The composting process kills weed seeds, and it will make better use of the nutrients. Hot composting above 140°F (60°C) kills pests and diseases. Many recipes are available on the Internet for horse manure compost. 

New straw bedding often uses much of the available nitrogen. The N-P-K runs about 0.6-0.6-0.4, with a full range of trace elements. Add horse manure a month or two before planting. It is best as an amendment and secondary source of nutrients. 

Rabbit Manure 
Rabbit manure is an excellent fertilizer that is high in available nitrogen and phosphorus. It can be difficult to find locally, except in Spain and via the Internet. Use rabbit manure as you would chicken manure. It breaks down and becomes available quickly. The N-P-K runs about 2.4-1.4-0.6 in this very soluble fertilizer with some trace elements. According to Dr. John McPartland, rabbit poop is the best. Bunnies rule!

Sheep Manure 
Sheep manure nutrient content is limited but it makes a wonderful manure tea. Sheep manures contain little water and lots of air. They heat up readily and make an excellent addition to compost piles. They add bulk, air, and nutrients. Use this inexpensive, low-odor manure as mulch, too. The N-P-K runs about 0.8-0.5-0.4, with a full range of trace elements. Add this slow-release soil amendment/fertilizer to planting mixes and compost piles more than a month before planting. 

Swine Manure 
Swine manure has a high nutrient content but is slower-acting and wetter (more anaerobic) than cow and horse manure. Difficult to find in a bag, most swine manure is available directly from the farm. Ask farmers for details on contents and use. Fresh, anaerobic lagoon sludge or liquid swine manure has an N-P-K of about 0.6-0.6-0.4. It also contains substantial ammonium and many secondary and trace elements. Add this hot manure to compost piles and to soil mixes. Be sparing with this manure because it is usually anaerobic in nature. 

Urine is mixed with barnyard manure. It adds readily available nitrogen and is good for organic cannabis gardens. Urine contains mainly water and urea. The odor of fresh urine dissipates quickly, especially when diluted. It does not attract flies and contains few pathogens. Urine is okay to use in an organic garden but synthetic urea is not. See “Haber process” at right. 

Be careful: It is easy to overfertilize with urine! Urine is packed with ammonia plants can’t assimilate and it acidifies the soil. Use with caution when applying in liquid form. Human urine can also be used as fertilizer and added to compost.

If your dog, horse, or goat urinates in the same place in the green grass yard, its urine will often burn grass if it contains too much urea. Burn patches are common when urea is repeatedly applied in the same place. I have seen “popular” metal streetlamp poles completely eaten through by dog urine. The N-P-K of urine runs about 12-1-2, and this soluble fertilizer is readily available. Normally it is mixed with animal bedding and manure so it is not as hot. 

Caution: Urine is loaded with ammonia that cannabis plants cannot assimilate, and it acidifies the soil. Use with care.

The Haber Process
The Haber process, also know as the Haber–Bosch process, is the chemical process used to extract nitrogen in the form of ammonia from the atmosphere. Ammonia is oxidized to make nitrates and nitrites for use in fertilizers and explosives. Synthetic fertilizer generated from the Haber process is believed to help generate one-third of the food in the world!


Coffee Grounds
Coffee grounds are slightly acidic—pH 6.0 to 6.2—and fine in texture. The high carbon-to-nitrogen ratio encourages acetic bacteria in the soil. Phosphorus, potassium, magnesium and copper in coffee grounds are readily available. The availability of nitrogen, calcium, zinc, manganese, and iron are low and sometimes deficient. Even though available nitrogen appears deficient, there are 10 pounds (4.5 kg) of total nitrogen per cubic yard (90 cm2) of coffee grounds. The nitrogen becomes available with microorganisms activity. In this way coffee grounds function as a slow release nitrogen fertilizer. Collect coffee grounds only. Remove paper that uses nitrogen to decompose. Keep coffee grounds in a covered container. This will preserve moisture and nutrients. Mix coffee grounds into soil surface and soil mixes before planting. Add no more than 5 percent coffee grounds to any soil mix or when sprinkling on soil surface.

Sugar Molasses, honey, and other sugars can increase soil microbial life, enhance regrowth, and make the plants’ use of nitrogen more effective. Molasses is the “secret ingredient” in many organic fertilizers and the natural sugar best for organic medical cannabis crops. Sucrose (corn) syrup is the most economical way to buy sugar. However, it lacks many of the qualities found in molasses.

Plants manufacture sugars. Plant roots do not absorb sugars, raw or refined. Bacteria and other soil life consume sugars as food or fuel. Adding organic sugar in the form of molasses to the soil increases soil life and biological processes around the rhizosphere or root zone. Decomposing sugars release CO2 and increase mineralization of organic elements. Molasses is practically useless in mineral-fed crops for mineralization.

Any sweet taste or flavor that vendors attribute to coming from sugars, does not come directly from adding sugars or flavorings to the nutrient solution. I would like to see vendors scientifically prove this cause-and-effect. Please have them contact me.

Unsulphured molasses is top quality and is used in cooking. This grade is made from ripe sugar cane juice that is clarified and concentrated. It can be used in the garden.

Sulphured molasses is made from unripe (green) sugar. Sulfur fumes are applied during sugar extraction. Afterward it is boiled repeatedly. First-boil molasses is of the highest quality because only a small amount of sugar is removed. Second and any subsequent boils turn the molasses dark in color and extract more sugar. It can be used in the garden.

Blackstrap molasses has been boiled three times to extract even more sugar. Mainly used as cattle feed, it is packed with iron. It can also be used in the garden.

Overall, the average N-P-K analysis of molasses is 1-0-5 and it contains potash, sulfur, and many trace minerals in a chelated form. It is also loaded with carbohydrates and a balance of consumables, which are a quick source of energy and food for microorganisms. Molasses can be purchased at hydroponic, grocery, health food, and livestock feed stores. Dilute it at the rate of one tablespoon per gallon (1.5 cl per 3.8 L) of water. Irrigate plants to feed organic life in soil. Start feeding soil life when plants are growing.

There are three main types of molasses: unsulphured, sulphured, and blackstrap.

Wood and Paper Ash
Wood ash (hardwood) supplies up to 10 percent potash. Softwood ashes contain about 5 percent. Potash washes out of wood ash quickly and can cause compacted, sticky soil. Avoid using high-pH alka-line wood ashes in soil with a pH above 6.5. Collect wood ash soon after burning, and store it in a dry place. Be careful when collecting fireplace ashes. Often such ashes are full of burned garbage that contains heavy metals and undesirable things. Collect and use only wood ashes from fireplaces, and apply sparingly.

Paper ash contains about 5 percent phosphorus and over 2 percent potash. Most inks are now soy-based or nonoil-based. I like to avoid paper ash due to the possible heavy metal content, but when clean and void of heavy metals found in some inks, paper ash is an excellent water-soluble fertilizer. Because the pH is quite high, do not apply paper ash in large doses.

Worm Castings 
Vermicast (aka worm castings, worm humus, and worm manure) are excreted, digested humus and other (decomposing) organic matter, the end product in the breakdown of organic matter by earthworms. Pure worm castings look like coarse graphite powder and are heavy and dense.

Worm castings are an excellent source of non-burning soluble nitrogen and many other elements. Vermicast is also an excellent soil amendment that promotes fertility and structure. Mix with potting soil to form a rich, fertile blend, but do not add more than 20 percent to any mix; vermicast is so heavy that root growth can be impaired. Vermicast is very popular and easier to obtain at commercial nurseries.

Vermicomposting can be done indoors, outdoors, or in a greenhouse. Red Wigglers (Eisenia fetida and Eisenia andrei) are the most active and commonly used worms in vermicomposting. Check the Internet for vermicomposting setups to turn your vegetable food wastes into rich fertilizer. 

Rock (Mineral) Powders 

Aragonite is biological and physical marine and freshwater precipitation-formed crystalline deposits of such shells as mollusk and oyster, which contain about 95 percent calcium carbonate. Use Aragonite to restore soil balance after applications of magnesium-rich lime that tie up other nutrients. Mined in Molina de Aragón, Spain, Aragonite is difficult to find in North America.

Ground into a fine powder, aragonite is used to adjust pH and raise calcium levels in the soil. It lowers acidity without increasing magnesium content. Avoid using aragonite with gypsum. 

This naturally occurring mineral contains micronutrients. Azomite consists of hydrated sodium calcium aluminosilicate derived from a natural volcanic mineral deposit. Add to compost or other fertilizer at the rate of 2 pounds (0.9 kg) per 10 square feet (.9 m2) and mix into soil up to a month before planting. Use in a 1 percent dilution in water. 

Biotite [K(Mg,Fe)3AlSi3O10(F,OH)2] is a dark mica sheet silicate. It contains available iron, magnesium, aluminum, silicon, oxygen, and hydrogen to form sheets that are weakly bound together by potassium ions. This is vermiculite and a source/concern for asbestos. Even though it also increases CEC of the medium, since even though the K is washed out, the bind sites remain. Biotite is also known as “iron mica” and black mica.” Phosphorus rock powders are available only when soil pH is below 7.0.

Diatomaceous Earth 
Diatomaceous earth (DE), the fossilized skeletal remains of fresh and saltwater diatoms, contains a full range of trace elements. DE is a good insecticide. Apply DE to the soil when cultivating or use it as a topdressing. It is more commonly used as an insecticide than as a source of calcium.

Dolomite Lime 
Dolomite lime adjusts and balances the pH and makes phosphates more available. It is generally applied to sweeten or deacidify the soil. It consists of calcium and magnesium, and is sometimes listed as a primary nutrient, though it is generally referred to as a secondary nutrient. Add dolomite lime to acidic soils and potting soils. Purchase flour or fine grades of dolomite that are available a little faster in the soil. Add dolomite a month or more before planting, at the rate of 0.5 cup per cubic foot (11.8 cl per 28.3 L) of soil. Use agricultural calcium if soil magnesium content is high.

Dolomite lime

Granite Meal 
Soft, fine granite rock powders contain trace elements in a water-insoluble, slow-release form. Granite forms naturally in many different chemical structures. Softer granite from the southeastern USA breaks down more easily than granite from the Northeast. Granite dust or granite stone meal contains up to 5 percent potash and several trace elements. Releasing nutrients slowly over several years, granite dust is an inexpensive source of potash and does not affect soil pH. Not recommended indoors because it is too slow acting. 

Epsom Salt 
Hydrated magnesium sulfate (MgSO4), Epsom salts, is a fast-acting soluble source of magnesium and sulfur. Use Epsom salts in alkaline soils to overcome magnesium deficiencies. Avoid using to raise pH in acidic soils; dolomite lime is a better choice. Apply Epsom salts (9 percent magnesium, 2 percent calcium, and 13 percent sulfur) when plants show a deficiency of magnesium. Continue adding weekly until symptoms disappear. Soluble magnesium sulfate washes out of soil quickly. Applying Epsom salts is also an outstanding way to leach out excess salts that accumulate in CEC mediums, especially sodium.

Epsom salts

Greensand (glaucomite) is an iron-potassium silicate sandstone rock. The minerals in which it occurs give it a pale olive-green tint. Greensand is a great source of potassium and trace elements and is used in many organic mixes. It is able to absorb ten times more moisture, making it an exceptional soil conditioner in potting mixes. It slowly releases its treasures in about four years. It is too slow-acting for indoor gardens but is a good long-term fertilizer outdoors. 

Greensand contains potassium, iron, magnesium, calcium, and phosphorus, plus as many as 30 other trace minerals. It is said to mineralize soil, improving plant and soil health by increasing populations of beneficial bacteria that make insoluble mineral nutrients available. Greensand is quite heavy and dense, with the consistency of sand, but can hold one-third its weight in water and has the ability to open tight soils and bind loose soils. 

In the USA, greensand is mined from ancient New Jersey–seabed deposits of shells and organic material rich in iron, phosphorus, potash (5 to 7 percent), and numerous micronutrients. Some organic gardeners do not use greensand because it is such a limited resource, yet at the same time it is used to make garden walls in parts of the UK. 

Greensand in the UK is often called “Upper” and “Lower” Greensand, which refers to two different deposits separated by Gault Clay. Lower Greensand (aka Woburn Sand) consists of a few deposits that contain of varying degrees of Atherfield (marine) Clay. Upper Greensand is a sand-based deposit within Gault Clay. Both greensands are found in the hills surrounding the London Basin and other sites in the UK.

Stay away from greensand coated with manganese oxide (aka manganese green-sand). It is used to remove insoluble oxidized iron and manganese from pipes.

Apply greensand as a long-term source of potassium and to correct potash-deficient soils. Apply up to 100 pounds (45 kg) per 1000 square feet (92.9 m2).


Gypsum, hydrated calcium sulfate, CaSO4·2(H2O), is similar to plaster-board used in construction. Granular gypsum is ground up into a fine, white powder that is more rapidly available to plants and soils. It contains 23 percent calcium, 19 percent sulfur, and trace amounts of potassium and magnesium. Gypsum converts (ties up) salts, including magnesium in soils, prevents crusty soil, breaks up and aerates clay soils, and regulates micronutrient uptake—copper, iron, manganese, and zinc in cannabis.

Gypsum works by pulling together clay particles in the soil to make bigger particles, creating porous spaces for air, water, and plant roots. For example, in saline-infused soil, gypsum removes sodium and replaces it with calcium. Gypsum adds calcium and sulfur to all soils. It also helps soil retain water and helps decrease soil erosion.

Calcium sulfate (CaSO4), aka Gypsite, is used to lower soil pH and improve drainage and aeration. It is also used to hold or slow the rapid decomposition of nitrogen. The formula carries calcium and sulfur in sulfate form. Cannabis is a major user of sulfur, and this is a great nutrient to add to any planting mix or compost pile.

Gypsite is unrefined gypsum that contains the clays and other minerals from the location it was mined. It is mined in arid areas, not typically wetter areas; it is not usually hydrated gypsum, CaSO4·2(H2O). 

Many states and provinces in the USA, Mexico, Thailand, and Spain have large deposits of calcium sulfate. Gypsum (CaSO4·2H2O) is one of the most common natural minerals and is really a type of rock. 

Natural Nitrate of Soda 
Natural Nitrate of Soda (NNS) aka Chilean Nitrate of Soda, is highly soluble, quick-acting granular fertilizer with 16 percent nitrogen in nitrate form, which is used directly by plants. This form of nitrogen is available to canna-bis in cold soils. Temperature-sensitive microorganisms also use this source of nitrogen. But NNS is high in sodium too! Do not use NNS on arid soils where salt buildup is common. It is mined from a desert in northern Chile, where the only known deposit of this mineral salt exists. Mix this nitrate with cocoa meal, peanut meal, compost, and other organic amendments to buffer sodium content. Applying NNS with organic compost increases efficiency of both amendments. The high sodium content makes NNS a poor choice for the main nitrogen source. N-P-K is 16-0-0 and 26 percent sodium in this very soluble fertilizer. Add with an organic amendment and do not rely on NNS for a sole source of nitrogen. NNS is not compatible with high-sodium contents found in arid and semi-arid regions. 

Rock Phosphate 
Rock phosphate (hard) is a calcium or lime-based phosphate rock that is finely ground to the consistency of talcum powder. The rock powder contains over 30 percent phosphate and a menagerie of trace elements, but nutrients are very slow to become available. 

Colloidal Phosphate 
Colloidal phosphate (powdered or soft phosphate) is a natural clay phosphate deposit that contains just over 20 percent phosphorus (P2O5), calcium, and many trace elements. It yields only 2 percent phosphates by weight the first few months. Apply colloidal phosphate to outdoor gardens for uptake of slow-acting potassium during the next four years. The rock powder contains 18 percent total phosphate (2 percent available), 19 percent calcium (27 percent CaO), and 18 trace minerals.

Potash is also the common name for several mined and manufactured salts that contain a water-soluble form of potassium. Typically measured in fertilizer as K2O, there are many chemical formulas depending on the source, collection, and form of potash. Occasionally potash will form with traces of organic plant remains. Potash was principally obtained by leaching the ashes of land and sea plants. It was refined from the ashes of broadleaved trees. Most potassium mines are in ancient deposits from inland oceans that evaporated. The potassium salts crystallized into beds of potash ore. The deposits are a mixture of potassium chloride (KCl) and sodium chloride (NaCl), aka table salt.

Potash rock supplies up to 8 percent potassium, and some deposits contain many trace elements. This slow-release fertilizer is not practical indoors but is a good long-term outdoor fertilizer and compost component. Potash is found in several different fertilizers, among them wood ashes and seaweed. 

Sulfate of Potash 
Sulfate of potash is normally produced chemically by treating rock powders with sulfuric acid, but one company, Great Salt Lake Minerals and Chemicals Company, produces a concentrated natural form. The sulfate of potash is extracted from the Great Salt Lake. 

In natural mineral form, sulfate of potash (K2SO4) contains more than 50 percent soluble potash and 18 percent sulfur as well as calcium and magnesium. The brands Sul-Po-Mag and K-Mag are natural mineral salts. These water-soluble products are made from langbeinite and contain about 22 percent potash, 11 percent magnesium, and 23 percent sulfur. Apply as a supplement or blend into soil when making organic soil mixes. 

The naturally occurring zeolite, clinoptlolite, provides a source of potassium that is slowly released. Some deposits also contain nitrogen that is slowly available over time. Zeolites also function to absorb more than half their weight in water and slowly release it as needed by plants. Incorporating zeolites into desert soils helps them withstand drought during hot dry weather.

Oyster Shells
Oyster shells are ground and normally used as a calcium source for poultry. Garden blends are pulverized to increase assimilation. Calcium formed in this non-crystalline state is more easily dissolved and utilized by the soil and plant. Oyster shells contain up to 55 percent calcium and traces of many other nutrients that release slowly. They are not practical to use indoors because they breakdown too slowly. Outdoors, oyster shells can be used as a long-term steady-release source of calcium and trace elements that raises pH in acidic soils. This is a good additive for compost piles and worm bins. Use 50 pounds (22.7 kg) of Oyster Shell Lime per 1,000 square feet (92.9 m2), depending on soil analysis and crop.

Seaweed meal and/or kelp meal should be deep-green, fresh, and smell like the ocean. Seaweed contains 60 to 70 trace minerals. Check the label to ensure that all elements are not cooked out. Kelp and seaweed are harvested from the ocean or picked up along beaches, cleansed of salty water, dried, and ground into a powdery meal. Cold-water kelp contains more elements. It is packed with potassium (potash), numerous naturally chelated trace elements, vitamins, amino acids, and plant hormones. It is often combined with fish meal to add N-P-K value. The nutrient content varies according to the type of kelp and its growing conditions. Seaweed meal is easily assimilated by cannabis plants, and it contributes to soil life, structure, and nitrogen fixation. It may also help the plants resist many diseases and withstand light frosts. Kelp meal also eases transplant shock. As an additive, cytokinins are most often derived from the kelp Ascophyllum nodosum. Seaweed is expensive to use as a bulk soil amendment unless it is locally available. 

Kelp is normally processed three ways, ranked in order of elements available: (1) enzyme digested (liquid), (2) cold-processed (usually liquid), and (3) extracts (meal or powder). 

Apply diluted solution to the soil for a quick cure of nutrient deficiencies.

Liquid seaweed is also great for soaking seeds and dipping cuttings and bare roots before planting. Also used as a foliar spray. 

Kelp liquid has a negligible N-P-K but is brimming with readily available micronutrients. Add kelp liquid regularly to gardens; it is immediately available and used within a month. Apply 1 to 2 tablespoons (14.8–29.6 ml) per gallon (3.8 L) of water and apply every 2 to 4 weeks. 

Kelp meal releases its cache of numerous trace elements 2 to 6 months after mixing it into the soil. Even with an insignificant N-P-K value, kelp meal is an excellent ingredient in potting soils. 

Kelp powder has an N-P-K of about 1-0-4 plus many micronutrients. It is an excellent ingredient as a soluble plant nutrient and source of micronutrients. Mix one-half teaspoon per gallon (2.5 ml per 3.8 L) of water and apply to containers once or twice monthly.

Vegetable Meals

Alfalfa Meal 
Alfalfa meal is an alternative to blood meal for nitrogen. It is balanced with phosphorus and potassium. It is available in meal or pellets that are commonly livestock feed, which has 17 percent crude protein content equivalent to 2.75 percent nitrogen. Meal and pellets, available in different sizes, are used to increase organic matter in the soil and also provide soluble nutrients, including trace minerals as well as triacontanol, a natural fatty-acid growth stimulant. 

Indoor, outdoor, and greenhouse gardeners use the pelletized livestock feed as a slow-release fertilizer. Alfalfa meal contains fiber and other substrates that feed populations of soil organisms. The carbon-to nitrogen ratio also speeds availability. Alfalfa meal is a great compost activator. 

Apply half a cup (11.8 cl) per plant for new plantings; one-half to a full cup (11.8–23.7 cl) to a depth of 4 to 6 inches (10.2–15.2 cm) deep around each plant. Medical cannabis garden beds need 2 to 5 pounds (0.9–2.3 kg) to 100 square feet (9.3 m2). Do not overapply. Rapid decomposition of alfalfa in the root zone generates heat, which can damage roots. The average N-P-K analysis is 2-1-2 that releases in one to four months. Find alfalfa pellets at feed stores. 

Alfalfa meal

Corn Gluten Meal 
Corn gluten meal materials have a high percentage of nitrogen. Allow at least one to four months of decomposition in the soil prior to seeding. The allopathic properties inhibit seed germination, but do not affect established and transplanted plants. This product is also marketed as a pre-emergent weed control for annual grasses. Remember, most corn is grown with GMO (genetically modified organism) seeds.

The typical N-P-K analysis is 9-0-0 with a release time of 1 to 4 months. Apply 20 to 40 pounds (9.1–18.1 kg) per 1000 square feet (92.9 m2).

Cottonseed Meal 
Cottonseed meal is the by-product of oil extraction and is a rich source of nitrogen. Many pesticides are applied to cotton crops, and residue remains in the seeds. According to the manufacturers, pesticide-free cottonseed is available. They say that virtually all chemical residues from commercial cotton production are dissolved in the oil and are not found in the meal.

Cottonseed meal can be combined with steamed bone meal and seaweed to form a balanced fertilizer blend. 

Cottonseed meal is often sold as livestock feed. It contains almost 85 percent water-insoluble nitrogen, and it will acidify soil. Nine pounds (4.1 kg) of lime will neutralize the acidity caused by 100 pounds (45.4 kg) of cottonseed meal. Remember, most cotton is grown with GMO seeds. 

The N-P-K is approximately 6-0.4-1.5, and the nutrients are released in 1 to 4 months. Till in 10 pounds (4.5 kg) per 100 square feet (9.3 m2) of regular garden soil.

Cottonseed meal

Peanut Meal
Peanut meal is available in southern states where peanuts are grown. It is high in nitrogen, but water-soluble nitrogen is limited. The average N-P-K is 8-1-2, and the meal is available long term.

Soybean Meal
Soybean meal is the by-product after milling and extracting oil from soy-beans. The meal is loaded in protein and is normally sold as a livestock feed. When mixed with soil, the microorganisms change proteins into amino acids and then break down the acids to make ammonium ions and nitrate ions, which are available for roots. Soybean meal acidifies the soil, lowering pH. The average N-P-K analysis is 7-2-1, and the nutrients are available in one to four months. Purchase soybean meal at livestock feed stores. Remember, most soybeans are grown with GMO seeds. Apply 8 pounds (3.6 kg) per 100 square feet (9.3 m2) of garden soil.

Compost and Compost Teas


Compost and compost teas are used by many organic gardeners as the only source of fertilizer. Outdoor gardeners love compost. It is inexpensive, abundant, and works wonders to increase water retention and drainage. Biological activity within the pile also increases nutrient uptake in plants. Indoors, compost is not as practical to use in containers unless it has been hot composted and is free of pests and diseases. Unfinished compost could have unwanted guests. If using compost indoors, make sure it is well-rotted and screened.

Compost piles need a mix of elements rich in nitrogen (N) and carbon (C). To ensure proper aerobic composting, the mix should be at the ratio of one part N and three parts C. 

Compost tumblers allow more aeration, which speeds decomposition.

Nitrogen-rich elements include: 
• Algae blood meal 
• Coffee grounds 
• Cottonseed meal 
• Fish meal
• Green garden clippings: grass clippings, weeds, leaves, etc. (Clippings must not contain chemical fertilizers or other chemicals, including weed- and-feed products used on grass.) 
• Legumes: alfalfa, clover, etc. 
• Manures: chicken*, cow, goat, horse, pig, rabbit, etc.* 
• Seaweed 
• Vegetable kitchen scraps

 *Salts are commonly found in uncomposted manures (chicken, cow, pig, horse, etc.) Decompose salts by letting them compost for at least 3 months. Bacteria, fungi, and other compost biology will dismantle, bind, and immobilize salts in the compost pile. Use a salt (Na) meter to measure salt levels in manures and composts. 
*Note: Chicken litter is often packed with different types of weed seed that are very difficult to kill with composting.

Carbon-rich materials include: 
• Cardboard, shredded 
• Corn stalks, including cobs 
• Dried (brown) leaves 
• Eggshells 
• Needles (fir, pine, etc.) 
• Newspaper, shredded 
• Paper, with soy-based ink if printed 
• Sawdust, in very small amounts and from wood not chemically treated 
• Straw 
• Woodchips, best if small or pulverized

Do not add: 
• Animal meat, fat, or grease 
• Ashes from chemically treated wood 
• Ashes from coal or charcoal 
• Bones 
• Cat, dog, or human feces 
• Dairy, cheese, milk, yogurt 
• Fish scraps 
• Meat 
• Oils 
• Potatoes 

The pile will also need: Air circulation, oxygen is essential to microbial growth in compost piles

Volume of at least 3 feet (0.3 m2) square (any less and heat dissipates faster than it is generated).

Fast, high-maintenance compost: 
Compost will be ready in 60 to 90 days, depending upon size and consistency of ingredients. Apply the list below to making compost for outstanding results. 
1. Confine the compost in a compost bin or use a freestanding compost pile. Cover or enclose the pile to protect from varmints. 
2. The volume of the pile must be at least 3 feet (0.3 m2) square. 
3. Lay out a 2-to-4-inch layer of bark chips or twigs. This will provide aeration from below. 
4. Combine materials at the rate of 1 part nitrogen to 3 parts carbon. Layer materials or mix thoroughly. Make sure all materials are in small pieces, which will speed decomposition. 
5. Add enough water to wet ingredients, but do not saturate. Pile should be like a wrung-out sponge. 
6. Cover pile with tarp to protect from excess rainwater or sunlight, which dries the pile quickly. 
7. Turn or stir the pile with a fork every 2 to 4 days. Check for even consistency of moisture. Stirring adds oxygen and moves cold outside particles to the inside and cooked particles to the outside. Pile will heat to between 100°F and 160°F (37.8°C–71.1°C) within a few days—even in cold weather. Temperatures above 131°F (55°C) kill most disease-causing pathogens along with seeds and weeds. 
8. Add water as needed to keep the pile the consistency of a wrung-out sponge. 
9. Compost is finished when the particles are small, uniform, dark brown and smell earthy.

Slow, low-maintenance compost: This compost will take a few months longer than the recipe above. This recipe is perfect for gardeners who have a little more time to compost. Use the recipe above and add ingredients as they become available. Piles with a volume less than 3 feet (0.3 m2) square will compost much more slowly.
1. Turn or stir the pile when it is convenient to do so. 
2. Do not add weeds or diseased plant residue, because pile will probably not get hot enough to kill pathogens, seeds, and weeds. 
3. Solarize used soil to kill pests and diseases. Compost piles must be at least three feet (91.4 cm) square to retain more heat than they give off.

Retail organic garden outlets often make actively aerated compost tea for their clients. This brewer makes tea 24/7.

Compost Extracts, Leachates, and Teas

The aim of compost extracts, leachates, and teas is to complement and improve compost/soil mixes rather than replace them. Outdoors the enhanced soil biology continues to improve soil for months after application.

Compost leachate is the dark-colored liquid that leaches out of the bottom of compost piles and worm bins. The solution is most likely rich with soluble nutrients, but it could also contain pathogens early on. The leachate works well to increase soil biology but in general is not a good foliar spray. 

Compost extract is made from compost suspended in a permeable bag (burlap, nylon stocking, etc.) in a container of water for one or two weeks. The extracted liquid fertilizer from this centuries-old technique is usually full of soluble nutrients and soil biology. The volume, richness, and brewing time of the compost determine the potency of the final extract.

Non-aerated compost teas are a mix of compost that serves as a source of biology and water. The mix is left to sit for a week or two and stirred occasionally. Anaerobic conditions created in the mix help plant pathogens flourish. Non-aerated compost tea could be detrimental to plants. Most pathogens that attack plants are anaerobic, living in low- and no-oxygen environments. It is easy to eliminate up to three-fourths of potential pathogens by aerating the solution.

Actively aerated compost tea (also called AACT or ACT) is actively brewed using compost, microbial foods, and catalysts added to the solution, which is aerated with a pump to infuse oxygen. The goal is to extract beneficial microbes from the compost and grow (and multiply!) populations of microbes during a 24-to-36-hour brewing period. Compost is the source of microbes. Microbial food (molasses, kelp and fish powders, etc.) and catalysts (humic acid, rock dust, yucca extract, etc.) encourage growth and multiplication of the microbes. Homemade ACTs are as potent as commercial natural or organic fertilizers or amendments. Under optimal conditions, the biology in the tea can increase more than 10,000-fold!

A growing number of farmers, gardeners, and horticulturists love aerated compost tea. It helps suppress pathogens such as Fusarium, Pythium, Phytopthora, and powdery mildew. Aerated compost tea also helps break down soil toxins and those found on plants by inhabiting the space around wounds and infections, thus denying entry to pathogens.

Properly brewed natural organic aerated compost tea cannot be overapplied. Food and oxygen levels are decisive as to the ability of microorganisms to reproduce and multiply. The aim is to maximize beneficial microbe growth without over-replicating, which uses all the avail-able oxygen and causes the tea to become anaerobic. Low- and no-oxygen teas can contain bad stuff including E. coli and root-feeding nematodes. Achieve this goal by keeping dissolved oxygen levels above 6 mg/L during all brewing.

Two kinds of aerated compost tea (ACT) include bacterially dominated compost, which is made with humus, vermicompost, and other sources of bacteria. This type of tea is best for annual cannabis. Fungal ACT is promoted and brewed with compost comprised of woody materials and is best for woody perennial plants. 

Less oxygen is available at higher elevations, and ACTs require longer brewing times. Brews made at temperatures above 90°F (32.2°C) need a shorter brewing time and often less food. Cold temperatures require a longer brewing time. The water’s mineral and chemical content will affect the final tea. Remove bacteria-killing chlorine and chloramines from water before adding compost.

Manure tea is made by placing manure in a permeable bag (burlap or nylon stocking) and suspending it in a container of water. The tea is left to steep for a few days to two weeks. Manure tea is dominated by anaerobic bacteria and other organisms. Pathogens and other bad things are most often present and can burn foliage or cause other problems when applied.

Take a look at the super-compost tea makers at There is a good “Organic Fertilizer and Amendment Guide” at:

Recipes for Five Gallons of Compost Tea

Compost tea: Add a shovelful of fin-ished, screened organic compost to a 5-gallon (18.9 L) bucket of clean water. Let soak for 7 days, stirring several times daily to add oxygen. Add a cup or two of alfalfa (pellets) to increase nitrogen if desired. Remove and apply one-quarter strength to full strength to outdoor containers or plants growing in soil.

Aerated compost tea: Use the above mix and add an air pump. Include an inexpensive aquarium air stone to make bubbles smaller and more dispersed, which will aerate the solution better. This will increase aerobic microbial growth. Add an eighth to a quarter cup of molasses (1 to 2 tablespoons (14.8– 29.6 ml) for every 3 days of brewing) to maximize microbial activity. This will boost soluble nutrient levels substantially. Further enhance the mix with catalysts, humic acid, yucca extract, and so forth. 

Aerobic tea is ready to use when it has either an earthy or “yeasty” smell or a foamy layer on top of the tea. 

Excellent Ingredients for the Compost Pile
Alfalfa meal or pellets: add extra nitrogen, proteins and bacteria Apple cider vinegar: adds about 30 trace minerals and acidifies the solution a little.

Brown sugar and corn syrup: are not as good as molasses 

Complex sugars, starches, and carbohydrates: rotten fruit, canned fish, etc., are best for fungal mixes 

Corn meal: adds nitrogen, proteins, bacteria, and has fungicidal properties 

Epsom salts: a tablespoon or three increases magnesium and sulfur levels 

Fulvic acid: increases trace elements and soil fertility 

Green weeds: Grind them up to quickly supply more food for bacteria

Humic acid: adds organic matter and water-holding ability to soils 

Molasses: available in liquid or powder; an outstanding sugar source for bacteriarich teas 

Organic garden soil: packed with aerobic bacteria, fungi, and other microbes 

Seaweed: supplies all trace elements and many growth hormones. But, after a short time they become inactive or break down entirely and add nothing to growth. 

Urine water: a potent organic nitrogen source 

Yucca extract: great soap-like spreader-sticker and also used as a human health-food supplement.

Do not keep compost tea for more than a day or two so that it does not turn aerobic or lose potency. Apply as a soil drench to increase microbial activities and supply soluble N-P-K and trace elements to soil. Foliar feed in conjunction with soil drench as a quick fix to nutrient deficiencies and to protect plants and control diseases. 

Do not use harmful liquid soaps or spreader-sticker agents when applying compost teas. Use molasses, fish oil, or yucca extract instead.

This 30-gallon (113.6 L) compost-brewing barrel makes enough compost tea to cover a 2,000 square foot (185 m2) garden.

Once set up, air is injected into the active compost mix for several hours.