The Growers Guide to Cannabis
The Growers Guide to Cannabis -

Pruning Cannabis during vegetative stage.

Pruning and training are common usages. Tomato growers pinch out side shoots, giant pumpkin aficionados remove all but one flower. Cannabis growers too have their own preferences for optimising their marijuana bud potential.

 General  marijuana pruning and training tips:

•  always use secateurs or sharp knife to avoid bruising
• when using ties, leave them loose enough to allow for plant growth but tight enough to support the stem.

Can you prune cannabis when its flowering?

Its generally to be avoided. Once you have flipped to flower at a cellular level the plant’s energies are no longer focused on growth but are making the transition to creating bud sites and later developing flowers. Pruning cannabis during veg works because the “cut” controls and diverts the growth hormones (see apical dominance in this piece on supercropping). Once the transition to flowering has been made, these growth hormones are hardly produced: in order to repair the damage caused by pruning, the plant has to divert energies away from bud production and into making growth hormones instead. This HAS to have an effect on total yield. There is a 10 days grace period (during pre-flower stretch) when the plant is still growing and begining to flower when you can get away with it, but certainly after this point: DON’T!!!

What about pruning cannabis leaves during flowering?

This is one of the most contentious practices amongst marijuana growers. Its very popular say in Spain where even the tomato growers remove large shade leaves during the flowering stage. The theory is that these leaves draw energy away from the buds and may indeed accelerate flowering maturation.And yes, we have seen some youtube vids and grow reports of plants almost fully stripped of leaves that look quite good.

BUT science tells us that pruning cannabis for maximum yield means avoiding pruning during flowering. The large fan leaves photosynthesize the energy needed for good buds, and even as the plant matures and the leaves turn yellow, it is better to let these gradually reabsorb the energy rather than shock the marijuana plant by pruning them. Leaf removal may even prompt sex change.

Here’s what the expert says:

Leafing is one of the most misunderstood techniques of drug Cannabis.cultivation. In the mind of the cultivator, several reasons exist for removing leaves. Many feel that large shade leaves draw energy from the flowering plant, and therefore the flowering clusters will be smaller. It is felt that by removing the leaves, surplus energy will be available, and large floral clusters will be formed. Also, some feel that inhibitors of flowering, synthesized in the leaves during the long noninductive days of summer, may be stored in the older leaves that were formed during the noninductive photoperiod. Possibly, if these inhibitor-laden leaves are removed, the plant will proceed to flower, and maturation will be accelerated. Large leaves shade the inner portions of the plant, and small atrophied floral clusters may begin to develop if they receive more light.

In actuality, few if any of the theories behind leafing give any indication of validity. Indeed, leafing possibly serves to defeat its original purpose. Large leaves have a definite function in the growth and development of Cannabis. Large leaves serve as photosynthetic factories for the production of sugars and other necessary growth sub stances. They also create shade, but at the same time they are collecting valuable solar energy and producing foods that will be used during the floral development of the plant. Premature removal of leaves may cause stunting, because the potential for photosynthesis is reduced. As these leaves age and lose their ability to carry on photo synthesis they turn chlorotie (yellow) and fall to the ground. In humid areas care is taken to remove the yellow or brown leaves, because they might invite attack by fungus. During chlorosis the plant breaks down substances, such as chlorophylls, and translocates the molecular components to a new growing part of the plant, such as the flowers. Most Cannabis plants begin to lose their larger leaves when they enter the flowering stage, and this trend continues until senescence. It is more efficient for the plant to reuse the energy and various molecular components of existing chlorophyll than to synthesize new chlorophyll at the time of flowering. During flowering this energy is needed to form floral clusters and ripen seeds.

Removing large amounts of leaves may interfere with the metabolic balance of the plant. If this metabolic change occurs too late in the season it could interfere with floral development and delay maturation. If any floral inhibitors are removed, the intended effect of accelerating flowering will probably be counteracted by metabolic upset in the plant. Removal of shade leaves does facilitate more light reaching the center of the plant, but if there is not enough food energy produced in the leaves, the small internal floral clusters will probably not grow any larger. Leaf removal may also cause sex reversal resulting from a metabolic change.

If leaves must be removed, the petiole is cut so that at least an inch remains attached to the stalk. Weaknesses in the limb axis at the node result if the leaves are pulled off at the abscission layer while they are still green. Care is taken to see that the shriveling petiole does not invite fungus attack.

It should be remembered that, regardless of strain or environmental conditions, the plant strives to reproduce, and reproduction is favored by early maturation. This produces a situation where plants are trying to mature and reproduce as fast as possible. Although the purpose of leafing is to speed maturation, disturbing the natural progressive growth of a plant probably interferes with its rapid development.

Cannabis grows largest when provided with plentiful nutrients, sunlight, and water and left alone to grow and mature naturally. It must be remembered that any alteration of the natural life cycle of Cannabis will affect productivity. Imaginative combinations and adaptations of propagation techniques exist, based on specific situations of cultivation. Logical choices are made to direct the natural growth cycle of Cannabis to favor the timely maturation of those products sought by the cultivator, without sacrificing seed or clone production.

Cannabis Botany from R.C. Clark.

Can you prune an autoflowering cannabis plant?

Well yes you can. We’ve regularly “topped” (see stem tip removal below) autos to produce a bushier plant. What you’ve got to remember though is that there’s only a short period of time in which to do this – but if you are growing a 10 week plus seed to harvest autoflower, you can get away with pinching out at the 4th set of leaves, and again at the 5th before the plant naturally makes the transition into flowering.

Read more about pruning autoflowers here

So what are the different types of pruning cannabis in order to get maximum yield?

Stem Tip Removal (meristem pruning)

Object: Shorter, bushier plant

Technique: Pinching out the main stem tip encourages those growing tips below the removal point to branch out. Use secateurs or sharp knife to avoid bruising

Timing: When the main stem has reached optimum height (20-30cm).

Disadvantages: Pruning the main stem late in plant development inhibits flowering  because it removes the meristemic tissues that sense light changes. Therefore unless there is a specific reason for delaying flowering, avoid in mature plants. Often combined with LST technique(see below)

Useful for:  Outdoor growing – makes a more discreet plant

Trellising

Object: Limits height of plants without pruning main stem

Technique:  Similar to growing grapes along a trellis. Insert posts into ground 1m – 3m apart, with

horizontal support wires at 30cm intervals. Marijuana seedlings are planted between the posts and as they grow are gently bent and attached to the supports with garden twine, training the limbs to grow horizontally. When flowers begin, these are allowed to grow upwards for maxium light.

Disadvantages: Need to have secure grow area – puts a number of plants in one place

Useful for: Outdoor growing

 Screen of green: SCROG

Object: Similar to a “Sea of Green” effect using training instead of multiple small plants. Planting

distance is 3 plants per m2..

Technique: When plants are 15cm tall,  pinch out to encourage short bushy growth (see meristem pruning above). A slightly slanted or horizontal framework of chicken wire is placed over the plants 30-60cm above growing medium. As plants grow during vegetative stage, they are trained horizontally underneath the framework and held in place with twine. As the marijauana plants are put into flower, the floral clusters are encouraged to grow upwards through the netting

Disadvantages: It is important to be observant. If the plants are left without training, the area becomes out of control and messy. Possibility of damage to the plant when bending stems – it can be fiddly.

Useful for:  Indoor grows with limited vertical space and lighting with limited penetration. Works best used with marijuana clones for uniformity of mature plant size and flowering time.

Low Stress Training Technique  (LST)

Object: Increases light penetration to a bushy plant

Technique: Place a framework around the plant and gently bend stems outwards and tie to frame (see photo). An alternative method is to weight the outer stems by tying weighted strings (ie with rocks) to pull the branches down and outwards.

Disadvantages: The weighted strings method makes the plant vulnerable in strong winds as the plant loses flexibility. This can lead to main stem splits

Useful for: Any bushy plant, indoor or outdoors

Limbing

This marijuana pruning technique removes the often unproductive lower shoots which never receive much light or develop anything but tiny buds, thus allowing the plant to concentrate its energy on the major flowers. Shock is minimised by removing the whole stem.

Supercropping: what is it and how does it work?

Supercropping means combining a number of pruning and training techniques to get the best out of your marijuana plant. It can include the techniques listed above, but also less common practices such as crimping and knuckling.  We’ve coined the phrase “extreme stress training” to describe some of these, and you can read all about them here

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