Vegetative growth – Chapter 6

The cannabis seedling growth stage lasts for approximately 2 to 3 weeks, from seed germination to (strong) root set. Once a strong root system is established, foliage growth increases rapidly and seedlings enter the vegetative growth stage. When chlorophyll pro­duction is full speed ahead, a vegetative plant will produce as much green leafy foliage and root growth as is physically and genetically possible. Of course, growing conditions—CO2, soil oxygen levels, nutrients, water, and so on—must not be limited and must be in the proper balance to be available for rapid uptake. Properly maintained, some varieties of medical cannabis will grow from half an inch to 2 inches per day. A plant stunted for any reason could require weeks to resume normal growth. A severely stunted plant may never fully recover.

Vegetative growth

Strong vegetative growth is essential to a healthy harvest.

Growing large plants in relatively small containers, in this case a 5-gallon (19 L) pot, requires daily irrigation with a complete nutrient solution. A layer of mulch would keep roots from being exposed.

These plants will spend a short time in vegetative growth and will be subject to fewer problems.

Vegetative growth in cannabis is maintained indoors, outdoors, and in greenhouses with 16 to 24 hours of light daily. Autoflowering (feminized) cannabis will flower according to chronological growth and is not affected by photoperiod.

A strong, unrestricted root system in a perfect rhizosphere (root zone) that is able to take in all necessary available nutrients is essential to robust growth. Unrestricted vegetative growth is the key to a healthy harvest. A plant’s nutrient and water intake changes during vegetative growth. High levels of nitrogen are needed. Potassium, phos­phorus, calcium, magnesium, sulfur, and trace elements are used at much faster rates. Transpiration is carried on at a more rapid rate, requiring more water. The larger a plant gets and the bigger its root system, the faster the soil will dry out. The key to strong vegetative growth and a heavy harvest is supplying plants with the perfect environment both aboveground and belowground.

During vegetative growth, plants need water and often need supplemental fertilizer too. Outdoor and greenhouse organic gardeners are able to build organic soil with bulk nutrients and amendments. Indoor gardeners usually need to add supplemental fertilizer. The garden will also need adequate air circu­lation and ventilation both day and night. Nutrient deficiencies that start during the first or second week of growth in­doors usually show outward signs by the third to fifth week of growth. Nutrient deficiencies that start during the fourth or fifth week of growth outdoors and in greenhouses show visible outward symp­toms during the sixth to eighth week of growth. Low-level nutrient imbalances can take longer to manifest, if ever.

Infestations of diseases and pests often flare as nutrient deficiencies progress. Many times new clones from another garden are already infested with spider mite eggs, powdery mildew, or root dis­ease, with few outwardly visible signs.
Always quarantine and dip new clones and seedlings in an organic fungicide/ insecticide/miticide before introducing them to the garden.

Multiple nutrient deficiencies, excesses, diseases, and pests become apparent during vegetative growth.

Cannabis flowers when given long nights and short days.

After 1 to 3 months of vegetative growth, nutrients have had a chance to build to toxic levels, and plants may show outward signs of deficiencies or excesses. Leaching containers will wash away water-soluble toxic nutrients. See chapter 21, Nutrients, for more infor­mation. Other problems—overwater­ing, underwatering, air circulation and ventilation, etc.—also occur now. See “Common Nutrient Problems” in chap­ter 21 for more information.

Cannabis will continue vegetative growth for a year or longer under an 18-hour photoperiod and a temperate climate. But sooner or later a genetic maximum is reached, causing cannabis to degenerate. Indica and indica-dominant varieties suffering stress from wintry conditions tend to flower regardless of hours of light, often producing more resin on stunted plants.

In this garden, mother plants and clones all grow under long 18-hour days with short 6-hour nights.

Indoors and in greenhouses, growth stages can be controlled with the light-and-dark cycle (photoperiod). It is the main stimulus to induce flowering. Give plants a 12-hour day and 12-hour night light schedule to induce flowering. Give plants 0 to 8 hours of darkness and 16 to 24 hours of light to retain vegetative growth. Controlling the photoperiod allows indoor and greenhouse horticul­turists to control vegetative and flower­ing cycles. See chapter 17, Light, Lamps & Electricity, for more information on photoperiod control. Outdoor gardeners work with Mother Nature and harvest after long nights and short days in spring and autumn.

Once a plant’s sex is determined, it can become a mother, clone, or breeding male and can be harvested or even rejuvenated (see chapter 8, Flowering).

Note: Plants show early male or female “pre-flowers” about the fourth week of vegetative growth. See “Pre-flowering” in chapter 8, Flowering.

Transplanting, pruning, bending, and trellising are all initiated when plants are in the vegetative growth stage. Informa­tion on these subjects follows.


When plants have outgrown their con­tainers, they must be transplanted in order to continue rapid growth. Inhibited, cramped root systems grow sickly, stunted plants. Signs of root­bound plants include slow, weak growth. Severely rootbound plants tend to grow straight up with branches that painstak­ingly stretch beyond the sides of the pot. By the time you see these symptoms, the plant is rootbound. To check roots, remove a plant from its pot to see if roots are deeply matted on the bottom or circling the sides of the pot.

When growing short plants that can be watered daily and reach full maturity in 70 to 90 days from clones or seed­lings, there is little need for containers larger than approximately 3 to 5 gallons (11.4–19 L). Larger plants and mother plants will need a large pot if they are kept for more than 3 months.

Outdoors and in greenhouses, plants can grow much larger than indoors. Containers should be as big as possible to accommodate a large root mass. Big plants that produce 10 pounds (4.5 kg) of medical cannabis buds can be grown in 200- to 500-gallon (757–1893 L) containers.

Transplant into the same type or similar growing medium; otherwise, a water pressure differential (hydroscopic tension) develops between the different mediums, which slows fluid movement and root penetration. For example, when a rockwool block is transplanted into soil, it holds more water than the soil is able to hold. Roots migrate slowly into soil. Transplanting small rockwool cubes into soil works best. Each cube holds little water, and roots migrate into soil faster. Make sure to keep the soil evenly moist and the rockwool semimoist to promote root growth into the new medium.

Starting seeds and clones in root cubes or peat pots makes them easy to trans­plant. Set the cube or peat pot in a hole in the growing medium, and ensure that the growing medium is in firm contact with it. Keep root cubes and substrates evenly moist after transplanting.

Transplanting is the second most trau­matic experience after severing the stem during cloning. It requires special at­tention and manual dexterity. Tiny root hairs are incredibly delicate and easily destroyed by light, air, or clumsy hands. Roots grow in darkness, in a secure environment. When roots are taken out of contact with the soil or an aeroponic garden for long, they will quickly dry and die.

Transplanting should involve as little disturbance to the root system as pos­sible. Water helps the soil pack around roots and keeps them from drying out. Roots need to be in constant contact with moist aerated soil in order to sup­ply water, oxygen, and food to the plant. But, the fine line is that these tender roots also need air (oxygen) so they are able to absorb nutrients and water.

Clones are ready to transplant once new, green growth starts.

The clones in this perfect Trichome Technolo­gies garden are easy to care for.

Fluorescent light is perfect for these recently transplanted clones. It gives them enough light to grow a strong root system and put on more green growth.

Good, strong roots must grow before cubes are ready to transplant.

A long vegetative growth stage lets cannabis plants get big enough to grow an abundant crop of flower buds.

Rockwool rooting cubes provide ready-made containers to root and transplant clones.

Dip Transplants in Miticide

Dip rooted clones and seedlings into a miticidal/fungicidal solution before transplanting. Stop diseases and pests before moving plants into a clean vegetative or flowering room. Mix a fungicidal/insecticidal/miticidal dip to disinfect clones before transplant­ing in the growing medium. Fill a container with low (5.0–6.0) pH water and add a natural fungicide such as hydrogen peroxide in a 3 percent solution. Or include a 10 percent mix of chlorine or vinegar. Do not mix chlorine and vinegar! The resulting gas is hazardous!

Mix the clone dip, and use a rag to cover and contain soil when dipping.

Submerge the entire clone in the dip to ensure liquid covers all foliage.

Remove the clone or seedling, and gently shake off excess dip before transplanting.

After transplanting, photosynthesis and chlorophyll production are slowed, as are water and nutrient absorption via roots. Transplant late in the day so transplanted plants will have all night to recover.

Transplants need subdued light so foli­age can grow at the rate roots are able to supply water and nutrients. Give new transplants filtered, less-intense light for a couple of days. If there is a fluorescent lamp handy, move transplants under it for a couple of days before moving them back under the HID, or into a green­house or outdoors to harden-off.

Ideally, plants should be as healthy as possible before being traumatized by transplanting. But transplanting a sick, rootbound plant to a bigger container has cured more than one ailing plant. Once transplanted, cannabis requires low levels of nitrogen and potassium and increased quantities of phosphorus. Any product containing Trichoderma bacte­ria or mycorrhizal fungi will help ease transplant shock. Plants need a few days to settle in and re-establish a solid flow of fluids from the roots throughout the plant. When transplanted carefully and disturbed little, there will be no signs of transplant shock or wilt.

Cutting the bottom off a biodegrad­able fiber or paper container is a simple transplanting technique that disturbs roots very little. Simply cut the bottom half out of the pot and set the plant in the planting hole. Remove the aboveground part of the container so that it is not exposed to air. If exposed to air, it will take longer to biodegrade and thus will impair root growth.

For more information on self-pruning containers and pots that promote and make a lot of roots, see chapter 19, Containers.

Always remove the plastic from rockwool cubes when transplanting!

This plant is rootbound and in need of trans­planting. Often such compressed roots have to be gently loosened before transplanting, so that they will grow outward and downward.

Seedlings and clones can also be trans­planted directly into 3- to 5-gallon (11.4–19 L) pots, a system that requires fewer containers and involves less work and less possible plant stress. The larger volume of soil holds water and nutri­ents longer and requires less-frequent watering.

When clones and seedlings in 4-inch (10.2 cm) pots are transplanted directly into 5-gallon (19 L) containers, the roots grow down, out, and around the container walls and bottom. In fact, the majority of roots will grow out of the soil and form a layer behind the con­tainer wall that is subject to temperature extremes.

To encourage roots to develop a dense, compact system, transplant just before a plant has outgrown its container. Trans­planting a well-rooted clone in a root cube into a 4-inch (10.2 cm) pot, and lat­er transplanting the 4-inch (10.2 cm) pot into a 3-gallon (11.4 L) pot or grow bag causes roots to develop a more extensive system in a small ball of growing medium. Successful transplanting causes minimal stress. Many cannabis crops are in the ground for such a short time that bungled transplanting costs valuable re­cuperation time and loss in production.

Transplant clones and seedlings into raised beds and large containers or planter boxes or directly into 3-to-5- gallon (11.4–19 L) pots. If plants are allowed to grow 6 to 7 months in full sun, 1 or 2 plants will fill a 200-gallon (757 L) container outdoors. When grow­ing for 3 to 4 months, containers can be 10 to 50 gallons (37.9–189.3 L) in size. Once plants start crowding and shading one another, bend stems outward and tie them to a trellis attached to the planter. Large planters require less maintenance than smaller containers or beds. The larger mass of soil retains water and nutrients much longer and more evenly. One downside is that all plants must receive the same water regimen and diet.

For more information on moving plants outdoors, see chapter 12, Outdoors.

Transplanting: Step-by-Step

Step One: The day before transplanting, water clones and seedlings with a half-strength mix of a product that contains Trichoderma bacteria and/or mycorrhizal fungi.

Step Two: Fill a 3-gallon (11.4 L) to 200-gallon (757 L) container with rich potting soil or soilless mix to within 2 inches (5.1 cm) of its top. Water the growing medium with a mild, quarter-strength organic nutrient tea or a salt-based hydroponic fertilizer solution until saturated and solution drains freely out the bottom.

Step Three: Carefully remove the root ball from the container. Place your hand over the top of the container with the stem between your fingers; turn the con­tainer upside down, and let the root ball slip out of the pot into your hand. Take special care at this point to keep the root ball in one integral piece.

Step Four: Carefully place the root ball in the prepared hole in the new con­tainer. Make sure the roots are growing downward, and the soil mass is level with or only a bit deeper than the new medium, slightly and firmly compressing (if necessary and possible) the entire new and old medium into a single unit.

Step Five: Backfill around the root ball. Gently but firmly place soil into contact with root ball. Add a top layer of mulch to conserve moisture and protect the del­icate layer of surface roots. In this case we used expanded clay pellets.

Step Six: Water with half-strength fer­tilizer containing Trichoderma bacteria and/or mycorrhizal fungus. Soil should be saturated—not waterlogged—and should drain freely. If rooting cube and new substrate are not identical, pay special attention to moisture levels. Let rockwool dry out enough so that roots penetrate new growing medium in search of moisture.

Step Seven: Place new transplants under fluorescent lamps on the perimeter of the HID garden, or under a screen to subdue sunlight outdoors or in a greenhouse for a couple of days. Once transplants look strong, move them under full light or into a greenhouse to harden-off.

Bending and Training

The goal of bending branches is to increase the number of bud sites per plant exposed to full intense sunlight or artificial light. More bud sites equates to more flower buds at harvest. The screen of green (SCROG) growing technique teaches gardeners to bend branches with the help of a horizontal trellis. Buds are bent out horizontally and produce more budding sites. In fact, a friend of mine published an excellent book for indoor medical gardeners: Secrets of the West Coast Masters, by Dru West (West Coast Masters, 2011). It is based on trellising to increase the number of bud sites, thereby increasing production.

Plant AgeContainer Size
1–3 weeksroot cube / soil block
2–6 weeks4-inch (10.2 cm) pot
6–8 weeks2-gallon (7.6 L) pot
2–3 months3-gallon (11.4 L) pot
3–8 months5-gallon (19 L) pot
6–18 months10-gallon (38 L) pot
Plant AgeContainer Size
1–3 weeks4-inch (10.2 cm) pot
3–6 weeks1–3-gallon (4–11.4 L) pot
6–8 weeks3–5-gallon (11.4–19 L) pot
2–3 months5–10-gallon (19–38 L) pot
3–6 months50–200-gallon (189.3–760 L) pot
6–9 months50–500-gallon (189.3–1893 L) pot

Pruning redirects growth hormones and affects plants more drastically than bending. Selective pruning and bending allow us to manipulate auxin hormone levels in branch and flower tips. Removing or bending a branch or branch tip causes hormonal balances to shift. Cutting the meristem (top growth tip) of a cannabis plant will diffuse auxins and cause greater concentrations in lower branch tips. Bending a growing tip changes hormone concentrations less than pruning does.

Use heavy aluminum wire to help support plants. This plant broke in the wind and was wrapped with duct tape. A piece of aluminum wire was wrapped around the branch to pro­vide extra support while the plant recovered.

Wrap wire around a broomstick to form a coil. The pliable coil of wire is much easier to wrap around branches.

There are many tie-downs to use when bending. Favorite tie-downs include the green insulated wire (bottom left) and the plastic-covered wire (bottom right). Twine, string, and ribbon must be tied and are more tedious to use. I prefer to use insulated wire that does not cut into branches.

Bending is similar to pruning, in that it alters the flow of hormones. Bend­ing efficiently neutralizes the effect of growth-inhibiting hormones and is much easier on plants than pruning. To bend, choose young, supple branches that are pliable. Lean a branch in the desired direction, and tie it in place. Young, supple branches can take a lot of bending before they fold over or break. Even if a branch folds, tie it in place; if necessary, use a wooden splint. The stem will heal itself. Young, supple branches take bending much better than old, stiff ones. Bending branches horizontally will encourage buds to grow vertically toward the light. Each bud will turn into an impressive flower top because they all receive more light. A wooden planter box with a lattice trellis alongside or nylon net above makes great anchors to tie bent plants to.

A ‘Jack Herer’ is growing in a 5-gallon (19 L) container in full sun on a walled balcony pro­tected from the wind. The initial bending starts as soon as the clone (moved from indoors) is established in the container.

Directing the branches outward by bending them toward the edge of the container will en­courage the plant to grow much wider so that all branches will develop bigger flower buds.

When to Bend and Train Branches

Bend plants when branches are still sup­ple enough to avoid injury. Especially on outdoor plants, branches lose pliability and become more rigid as they age. For best results, start bending plants before they are 12 inches (30.5 cm) tall so that branches have time to adjust hormone levels and grow evenly.

When grown in the vegetative stage for more than a month or two, plants may need to be bent and trained over a longer season. Once plants enter the flowering stage, bending becomes increasingly more difficult. Bending is less fruitful after flowering plants initiate the last upward spurt of growth.

Wire ties, the kind used to close plastic bags, can be purchased at a nursery. Wire ties are either precut or cut to length by the gardener. Use these ties on small plants that need little direc­tion. Wire ties are generally too small for larger plants and can cut into stems. Thicker ties made of plastic-coated elec­tronic wire or telephone cable work well. They are fastened with a simple twist and stay rigid, leaving the stem room to grow. If applied too tightly around a stem (girdling), liquids cannot flow, and death could result. See “Trellises & Ties”.

Use grafting tape (or green plastic plant tape with no glue) to cover and support broken branches. A small stick can be used as a splint for extra support. It pro­tects the wound and also holds broken branches in place. I used duct tape on this plant and was lucky, since the glue can cause issues. Duct tape also stretch­es and breathes with the plant.

Be gentle when bending branches, even though plants can take some abuse. Sometimes a crotch will separate or a branch will fold over, cutting off fluid flow. These mishaps are often easily fixed with a small wooden splint snugly secured with duct tape to support the split and broken stem. But sometimes a branch broken at a crotch cannot be repaired.

Gardeners also combine pruning and bending. It is easy to prune too much, but it is hard to overbend.

As the plant grows, its branches are bent fur­ther outward. The branches in the center of the plant will receive more light and will develop quickly.

The foliage has grown and the bent plant is showing nice form. The large plastic netting will soon fill with foliage.

It is early summer, and the plant is well estab­lished. The larger trellis is accommodating the extra growth, and bending is continued.

The plant is starting to bud up and has formed a huge canopy over the small container.

A plastic-coated wire tie was used to bend this branch down to keep it from growing over the 8-foot (2.4 m) fence.

The plant is now in full bloom. It nearly fills a large part of the terrace, completely covering the plastic trellis visible earlier.

Duct tape can work well to repair broken branches.

A pyramid of twine is suspended overhead to hold up bud-laden branches. These plants were started from seed normally grown indoors, and their branches are weak. The trellis helps keep the heavy branches upright.

Trellises and Ties

Medical cannabis plants that grow more than 3 to 4 feet (91.4–122 cm) tall often need to be trellised so that weighty buds do not cause branches to break. Trellises serve to direct plant growth within a given space, and take advantage of sunlight. Adequate trellising also keeps plants standing with minimal damage after rainstorms. Complicated, poorly planned trellises get in the way when maintaining a garden. Plan a simple, easy-to-use trellis. Some gardeners use bamboo stakes or a tomato cage anchored in containers. Raised-bed gardeners can build a frame to set up horizontal trellis netting over plants; branches full of flower buds grow through the netting.

Outdoor gardeners can set up hoop-house trellises over plants by covering the hoop house with 6-inch (15.2 cm) plastic netting, after using the same hoop house as a greenhouse. Branches grow through the trellis netting. If branches grow and start to droop after the first net is in place, wait until they are about 2 feet longer and throw another 6-inch (15.2 cm) net over the plants as a second trellis.

Building your own circular wire trellises is a good option for big plants. Large tomato baskets work well for medium-size plants. Buy 3- to 6-foot-tall (122–182.9 cm) lengths of galvanized wire fence made from 6-inch (15.2 cm) squares. Form the fence into a big circle 3 to 4 feet (91.2–122 cm) in diameter. Cut and bend the ends of wire to connect the basket into a cylinder. The result will be a 6-foot-tall (182.9 cm) trellis that is 3 to 4 feet (91.2–122 cm) across. Set it over plants before they grow too big. Anchor the trellis in the ground with large staples or tent stakes. 

The ‘Flo’ plants in this garden are destined to grow outdoors. Lower branches and leaves will be stripped before transplanting deep in the soil.

The plants in this greenhouse are trellised with large tomato cages. They will grow to fill the greenhouse and will soon need new trellises.

The plastic has been removed, and this hoop house is now a trellis for some very big plants. It is near the first of June, and these established plants are ready to grow!

By August 20, the plants have grown through the first netting-trellis and a second netting-trellis has been applied over the top.

Prune lower growth that receives little or no light. These little branches produce small buds that are difficult to harvest.

This short plant was pruned once by removing the meristem.


Pruning redirects growth hormones and affects plants more drastically than bending. Selective pruning allows gardeners to manipulate auxin hor­mone levels in branch and flower tips. Removing a branch or branch tip causes hormonal balances to shift. Cutting the meristem (top growth tip) of a cannabis plant will diffuse auxins and cause greater concentrations in lower branch tips.

Always use clean instruments when pruning. A straight razor, single-edge razor blade, a sharp pair of pruners or scissors—all work well for different applications. Sanitize clippers and blades between cuts by dipping in rubbing alcohol* or bleach, or flame with a torch. Use indoor pruners only in the indoor garden. Pruners used outdoors have everything from spider mites to fungus spores on them. If outdoor clippers must be used, dip them in rubbing alcohol, or flame with a butane torch to sterilize before making cuts. After pruning, the open wound invites diseases and pests. Wash your hands and tools before and after pruning. Make cuts at a 45-degree angle to discourage moisture from sitting on wounds.

*Alcohol works but it is not 100 percent effective, especially on spores and virus particles. A 10 percent bleach solution or a commercial sanitizer will work 100 percent of the time.

Avoid pruning for a month (or more) before inducing flowering. Since pruning diffuses floral hormones, flowering is retarded. If cannabis is pruned heavily 4 to 6 weeks before flowering, peak maturation will be delayed for a week or longer. It takes a month or more for hormones to build up to pre-pruning concentrations.

Leave leaves alone! Removal of healthy leaves hacks up a healthy plant. Remov­ing strong, healthy leaves DOES NOT make plants more productive, even though this practice supplies more light to small leaves and growing tips. Plants need all their leaves to produce the max­imum amount of chlorophyll and food. Removing leaves slows chlorophyll pro­duction, stresses the plant, and stunts its growth. Stress is a growth inhibitor. Remove only dead leaves or leaves that are more than 50 percent damaged.

Remove sickly lower growth that receives little light. This weak growth is a ready environment for diseases and pests to attack. Removing shaded lower growth will also increase air circulation between and around plants. 

Pruning all the branches or removing more than 20 to 30 percent of the foliage in a short time frame may cause plants to suffer so much stress that harvest is diminished, especially if there is a short recovery time. However, growth and pruning also depend upon plant health, conditions, stem girth, and other variables.

Over time pruning too much may alter hormonal concentrations, causing spin­dly growth. This is often the case with mother plants that provide too many clones. Mother plants that are up to 12 months old provide the best clones. Many gardeners keep mothers for only 6 months.

Pruning outdoor plants early to mid-season does not affect harvest time. Hormones have a chance to relocate and stabilize before harvest. Pruning branch tips and the main growing shoot forces growth down to lower branches and may be necessary to keep plants under control in small gardens.

Prune plants when small to have the most effect on branching. Removing top growth early will leave a few lower branches to grow upward. Pruning top or side branches later in life will have less dramatic effects and affect hormonal balance less due to the abundance of foliage and hormones.

For the most part, pruning and remov­ing weak spindly growth and dead leaves is all the pruning necessary. See “Remove Lower Branches,” below.

An expert medical cannabis gardener from Humboldt County, California, has a unique pruning style for giant plants. The meristem is made to form a callus by cutting it—similar to the FIM technique. Once a callus forms at the tip of the meristem, it is split into 4 separate pieces. The 4 separate quarter-branches are splayed out at 90-degree angles and trellised. The insides of the stems heal rapidly, and branch shoots start growing upward.

The plants in this garden were too tall when moved in from the vegetative room. They grew fast and the light was able to penetrate only the first 2 feet (61 cm) of foliage. Removing lower growth sends energy upward and increases air circulation below. Nonetheless, plants were growing too long under poor conditions. This is why lower leaves were removed and both time and resources were wasted.

The main stem of this cannabis plant was split to form 4 branches. The wounds on each of the split branches heal and form 4 new “main” stems. This unique, labor-intensive pruning technique promotes the most growth and budding sites from a single cannabis plant. This technique is effective when plants are grown for 6 to 10 months and all other elements —soil, water, nutrients, light, etc., are kept at optimum levels to support the extra growth.

The lower branches on this outdoor plant have been removed because they receive little light and would produce spindly buds. Removing shaded, spindly lower growth increases air circulation and sends valuable growing energy to plant tips.

Pruning Techniques

No Pruning

Not pruning has several advantages. Floral hormones are allowed to con­centrate in tips of branches, causing flower buds to grow stronger and denser. Indoors, short, unpruned plants can be crammed into a small area. Crowd­ed plants have less space to bush out laterally and tend to grow more upright. Clones are set into the flowering room after 1 to 30 days in the vegetative room.

Little clones are clustered together in 3-gallon (11.4 L) pots.

Many indoor gardeners do not prune at all, especially when growing a short clone crop that is only 2 to 3 feet (61– 91.4 cm) tall. Short clone crops require no pruning to increase light to bottom leaves or to alter their profile. “No pruning” is the easiest and most produc­tive method when growing short crops, but branches heavily laden with flower buds may need to be trellised.

Outdoors, not pruning is common. Gardeners in Northern California let plants grow to their potential and throw trellising netting over plants to support branches full of flower buds. Many short, stout plants that grow up to four feet (122 cm) tall and are not pruned do not need to be trellised.

Remove Lower Branches

Remove spindly branches and growth that is not collecting light energy, including dead and dying leaves. Remov­ing weak, light-starved lower branches is common in outdoor, indoor, and greenhouse gardens alike. Pruning lower branches concentrates growth in upper branches. Cut lower branches off cleanly at the stem so no stub is left to rot and attract pests and diseases. If you must harvest a little medicinal cannabis early, removing a few lower branches will least diminish the harvest.

Pruning out spindly branches and growth inside plants opens up the interi­or and provides better air circulation. It also makes inspecting soil, plant stems, and irrigation fittings easier. This is a much better practice than removing all lower leaves.

Remove All but Four Main Branches

Remove the plant’s meristem (central stem) just above the 4 lowest (main) branches. Removing the central leader concentrates the floral hormones in the 4 remaining branches. The resulting fewer branches will be stronger and will bear a larger quantity of dense, heavy flower buds. Remove the stem above the 4 main branches, but do not remove leaves on the main branch­es. Select plants with 3 sets of branch nodes about 6 weeks old and pinch or prune out the last set of nodes so that 2 sets of branches remain. Move plants into the flowering room or greenhouse when they are about 12 inches (30.5 cm) tall. To maintain a low garden profile, varieties that grow fast and tall, such as ‘Critical Mass’, ‘Power Plant’, and similarly robust bloomers, should be set in the flowering room or greenhouse when about 8 inches tall.

This humongous, pampered plant is growing in a 500-gallon (1893 L) container in a green- house. The two 1-gallon (3.8 L) containers on the right add perspective to this plant that has just started to bloom.

Bend or fold plant tips over to practice super-cropping. This practice sends energy down to lower branches.

Plants often heal, and the tip of the plant once again is able to orient growth upward.

Establish a bud count before pinching because only the next lower 5 to 7 buds will actually break or open and grow properly. If the plant is 10 leaves or nodes taller, a soft pinch of only the meristem and 1 leaf, will probably give about 5 breaks. If the plant is 15 leaves or nodes tall, then a soft pinch will give the same results, but all high on the plant. A harder pinch, the top 3 to 5 nodes down, may cause 3 to 5 good branches to grow below. This is a slower process that can extend the maturation period but adjusts the height overall.

Pinching Branch Tips

Pinching back or pruning tops (branch tips) causes the 2 growing shoots just below the cut to grow bigger and stronger. The effect is echoed down the plant. Pinching back and pruning branch tips increases the number of budding sites. It diffuses floral hormones (auxins). At high concentrations, auxins prevent lateral buds from growing very quickly. Lower branches develop more rapidly when the top of the plant (terminal bud) is removed. The further the tip of the branch is from hormones, the less effect the auxins have.

To pinch back a branch tip, simply snip it off below the last set or two of leaves. Pinching off tender growth with your fingers helps seal the wound and is often less damaging to plants than cutting with scissors or pruners. When the main stem is pinched back, side and lower growth is stimulated. When all the tops are pinched back, lower growth is encouraged. Continually pinching back, as when taking clones from a mother, causes many more little branches to form below the pruned tips. Eventually, the plant is transformed into a hedge-like shape. Most gardeners do not pinch plants back, because it diminishes the yield of prime, dense flower tops; but it may not affect the overall dry weight. Promoting many small buds also requires more work when trimming harvested buds.


Super-cropping is a form of pinching back or pruning branch tips. Regardless of who coined the buzzword, there are several different versions of super-cropping used by cannabis gardeners.

The theory of super-cropping is that plants respond to impaired fluid flow by producing more cannabinoid-rich resin and compact female flowers. The branch is folded over, approximately 2 to 3 inches below the growing tip, creating a wound. Some gardeners swear by this practice, and there might be a morsel of truth in it.

Super-cropping can also incorporate FIM pruning, which is explained below. It can be combined with bending, too. Removing healthy leaves so that “bud- ding sites receive more light” is also practiced by some super-croppers who claim higher production. See “Stress,” for more information.

FIM Technique

The FIM technique first appeared in print in the July 2000 issue of High Times magazine. According to the best information I could find, the technique was started by a gardener from South Carolina. He tried to pinch the tip of a plant and said, “F%&k, I missed!” (FIM) when he did not remove the entire bud as desired. Once the growing tip was pinched, or FIMed, the gardener left the plant to develop. Many different flowering tops formed as a result of this single pruning. According to some cannabis gardeners, this technique increases yield. However, my experience has been that it does not. FIM pruning also creates a small, dense flower top that is prone to disease.

The drawing in the center and the close-up on the right show the FIM pruning technique—the bottom 10 percent of the bud remains intact. This is the key to FIM pruning.


Little is known about grafting cannabis, and it is seldom practiced, which is why grafting commands a small place in the medicinal cannabis garden. Grafting cannabis will help solve drought and possible root-disease problems. Grafting an indica stock with a com- pact growth habit to a large sativa root system provides more nutrients for the aboveground plant. The resulting plant would be a drought-resistant super plant.

Most medical states in the USA impose a maximum number of plants we are able to grow. Grafting 3 or 4 different varieties onto 1 mother plant would help a gardener stay below mandatory plant maximums.

Yes, it is possible to graft cannabis rootstock onto a scion (branch) of hop species (Humulus lupulus). Hops, the female flower clusters from hop plants, are used in the production of beer. The plant will live; however, it will not pro- duce more cannabinoids.

The top green part (scion) of one cannabis plant is grafted onto the rootstock. Sativa varieties are generally more disease-resistant than indica varieties. Grafting sativa rootstock onto indica varieties may help make plants more disease resistant.


Cannabis grows best and produces most heavily when it is given a stable environment. Stressed plants are less productive than unstressed plants. Stress-induced traumas include withholding water, photoperiod fluctuation, low light intensity, ultraviolet light, nutrient toxicities and deficiencies, cold and hot soil, temperature extremes, mutilation, and any other weird stuff beyond ideal growth conditions. In addition, any overt applications of growth hormones such as gibberellins, cytokinins, abscisic acid, ethylene, or colchicine cause stress. Stress can also cause female plants to produce male flowers and male plants to produce female flowers. See chapter 22, Additives, and chapter 25, Breeding, for more information on hormones and other agents.

Stress can cause plants to produce more resin, but it simultaneously causes odd and/or less growth. For example, Felix, a Swiss outdoor gardener, grew a fi eld of cannabis at 900 feet elevation (274 m) and another at 4200 feet (1280 m). The upper field suffered stress because it was exposed to cooler temperatures and more ultraviolet radiation. Plants there produced about 25 percent more resin-packed THC than plants in the lower field. But, plants that grew at 900 feet elevation (274 m) yielded at least 25 percent or more dry weight than plants at 4200 feet (1280 m). Removing large green shade leaves allows more light to shine on smaller leaves, but it also causes growth to slow and harvest to diminish. Remove only leaves that are more than half damaged by pests or diseases. Often, partially yellow leaves green up once stress is eliminated.

These plants—grown under stressful conditions in the Rif Mountains of Morocco— receive more intense UV light, limited nutrients, and little water.

The branches on this “bonsai” plant have been pruned, as have the roots, so that it will grow slowly in this small container. The stressful environment keeps the plant small.

How to Make Cannabis Plants Suffer Stress

1. Photoperiod fluctuation and then back to a 12-hour day/night photoperiod.

2. Low light intensity (This may cause more male plants.)

3. Nutrient toxicities and deficiencies

4. Cold and hot growing mediums

5. Cold and hot ambient temperatures

6. Mutilation

7. Sex stress

8. Watering

9. Pathogens

10. Chemicals

11. Much more

Mutilating plants by breaking the trunk, driving a stake through stems, and otherwise torturing or slapping them around might increase resin production, but most often the resulting stress retards growth, causes other problems, and reduces overall production.

Withholding water may also cause more resin production, but it impairs growth and diminishes leaf, stem, and flower production. Water stress slows or stops clones from rooting. If clones have too many leaves and are too busy transpiring, root growth is very slow. Conversely, waterlogged rooting mediums harbor no air, and rooting is then slowed to a crawl. 

Stress can also affect plants’ sex. See chapter 25, Breeding, for more information.