Prune cannabis plants is a very common technique to increase yields of plants per crop. Growers can prune marijuana plants during vegetative stage, during its flowering stage, or both, to get different reactions. In this post we will detail when and how to prune cannabis plants to get desired results.
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Prune cannabis plants in vegetative stage
In previous chapters we've talked about the famous FIM technique, to multiply quantity of shots per plant. Today we will explain benefits of pruning plants, and how to do it to get the desired effect.
Plants in vegetative stage develope their natural structure with a one and only main cola, that gets most of the available energy from the plant. The technique of pruning the top of the plant is based in cutting the top part of it, so the plant, naturally, starts developing with more than one top.
This technique is often used in many strains due to three main reasons:
Cover the maximum horizontal space.
Control the height of the plants.
Avoid losses due to a lack of airflow and to fungi attacks.
-The first case benefits growers that usually work with less number of plants per squared meter, that need every one of the plants uses the maximum space, to don't miss any ray of the light used.
-In the second case, pruning cannabis plants will force them to divide its energy in multiply colas, so the vertical growth will be slown down (specially interesting in sativa dominant strains that trend to stretch when turned to flowering.
-The third option is often called "a pain in the ass for a big buds grower". Some strains develope huge, and dense, flowers that usually suffer from botrytis (grey mold) in its inside. This mold can send your complete crop to trash, so some growers prefer to do some toppings to their plants, to divide the size of its flowers in many tops (smaller buds per cola, but more colas instead of one and huge).
*If we are interested in controlling the height of cannabis plants (so they don't grow as big) it is important not to cut lower parts of the plants while they are in growing stages. To do so would increase the available energy into top part to grow even more.
When and how to top marijuana plants during growing phase
Marijuana plants indoors usually grow with thinner stems compared with those grown outdoors. This point makes it easier to growers when they what to prune plants, because it is just needed some pruning scisors.
How to prune cannabis plants is an art learnt with practice, but with a known target: Look for a cutting point, under wich two shots exists, that could develope with equal height.
What is important before cutting the top (topping) is to focus on two main points:
-How many shots with similar height exist under the cutting point?
-What height will I cut the plant next, and how many shots under the cut will remain.
The importance of these aspects is easy to explain: Bigger the number of shots under the cut, more shots we'll get after pruning, all with the same height. Also better homogeneity in plant's height, will become in easier job to keep the grow-light at equal distance from canopy.
As an answer to When to prune plants, it depends on two factors: Plant's size and available height. In plants born from seed it is recommended not to prune plants until its 5th real node (about 25 cm height). If we're using cuttings we can start pruning whenever we want.
Referring to available height in the grow-room: As we said before, multiplying the number of colas of a plant divides its growing performance in the number of main colas. This way growers with less available height can grow without fear of plants reaching the maximum height (too close to the grow-light).
The recomendation once the topping is made is to keep the plants in vegetative phase enough so the top shots (new main colas) develope before switching lights to 12/12 (recomended time of about 7 days).
Unlike plants in vegetative stage, marijuana plants in flowering stage don't develope as much its shots, so we should never do a topping once we've flipped plants to flowering.
*If, for any reason, flowering plants have grown too much, and we must do a cut to avoid plants get burned due to being too close to the lights, it is important to do it as early as possible, because all those flowers formed in the top zone will be lost without remedy.
Prune plants in flowering phase
Prune plants at the early flowering stage helps in two ways:
Favours the airflow on the bottom of our grow-room, allowing the air to easily flow allarround.
Helps directing plant's energy to the top part of the plants, where it will be proffited to form bigger and thicker buds.
Pruning low branches of the plants will help them not to loose energy in lower buds that percieve low light, and usually not maturing at the same time the rest of the plant does.
When to prune plants in flowering stage
If we like to get maximum profit from our plants it is necessary to wait them to start flowering. In some indica strains this will occur after 10-12 days of changing photoperiod to 12/12, while other strains sativa dominant usually occurs 15-20 days after flipping to 12/12. The best moment to proceed with the pruning of lowest branches is a week after first pystils appear (moment we can see not only 1 or two white hairs, but we see the plant is starting its flowering).
How to prune marijuana plants in flowering
Pruning of lower branches is based on free plants from unnecessary branches and leaves for its correct evolution. For this step we recommend using bud clean scissors, that will make clean cuts without damaging plants.
these cuts should be done close to the main trunk, deleting any possible future developement in the future.
The quantity of branches to prune depends on the total height of plants: Bigger the plant is more branches should be cut.
As a refference, from SantYerbasi we like to recommend cut about a 30% of the total height of the plant:
I.e.: A plant of 30cm height we should cut off all branches and leaves born in the first 10cm from substrate, while to plants of about 1,20m height, we should cut them all branches and leaves appeared in the first 40cm from the pot.
At this point it doesn't matter if the branch arrives up to the top or not, we should cut it out so all shots over it recieve the extra energy that allows them to take better profit of the light recieved.
*In cases of SCROG type gardens, or the ones using Low Stress Training method, instead of cutting the whole branch (what would end in lower yields), it is better to cut sub-shots appeared along the lowest part of that branch. This way we get the same effect without loosing the cuoted branch.
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