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.
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.
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.
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.