Pruning is the removal of excess foliage. It’s a pretty common practice among cannabis growers, as it allows plants to allocate more of their energy resources to bud development. Decluttering a plant also ensures that all bud sites receive maximum light exposure and improves airflow. Surprisingly, however, new research has revealed that pruning cannabis plants twice may be the most effective way of increasing cannabinoid yields.
Pruning Optimises Cannabis Plant Architecture
Pruning is far from the only way of altering the structure of a cannabis plant. Generally, the practice involves the removal of leaves, branches, and nodes, yet some growers prefer to stick to gentler methods like defoliation, which only entails the removal of leaves. The authors of a new study experimented with eight different “plant architecture manipulation treatments” before measuring how these affected inflorescence yields and cannabinoid concentrations to determine which technique is most beneficial.[i]
Their results indicated that defoliation allows the most significant amount of light to reach flowers lower down the plant, resulting in a more uniform cannabinoid profile. Under other configurations, reduced light intensity closer to the ground caused some buds to generate much smaller concentrations of THC, CBD, and other compounds, resulting in an uneven spread of cannabinoids throughout the plant.
Overall, however, they found that pruning cannabis plants twice – once during the vegetative stage and once as the photoperiod was shifted to initiate flowering – gave the greatest overall cannabinoid yield. ‘Control’ plants that were allowed to grow naturally without any form of architecture manipulation produced an average of 0.794 grams of tetrahydrocannabinol acid (THCA – the carboxylated form of THC) and 14.099 grams of cannabidiol acid (CBDA, which is converted to CBD upon decarboxylation). However, double pruning their cannabis plants substantially boosted these values, causing each plant to generate 1.119 grams of THCA and 22.446 grams of CBDA.
It’s important to note that this experiment was conducted using a single high-CBD cultivar and that these results may not necessarily be reproducible with other strains. Intriguingly, the same researchers published a second, virtually identical study this month, with the only difference being that this time they conducted their defoliation and pruning experiments on two separate cannabis cultivars. They were able to determine that architecture manipulation does not always produce the same effect when applied to multiple strains and that a plant’s genotype influences how it responds to these techniques.[ii]
Is Pruning Cannabis Necessary?
As previously mentioned, not everyone is in favour of pruning their cannabis plants, and those that are will typically do so with a great deal of care and caution. Plants can be encouraged to strengthen and nourish the remaining buds by strategically removing branches and nodes, resulting in larger flowers and higher cannabinoid concentrations.
However, pruning also stresses cannabis plants, so it should only be practiced on healthy individuals and never during the flowering stage. The study results mentioned above certainly make for interesting reading, but they shouldn’t be taken to mean that all cannabis plants will respond well to double pruning.
Ultimately, there’s no one-size-fits-all approach, and it’s up to each grower to experiment and get to know their plants to determine whether or not to prune.
[i] Danziger N, Bernstein N. Shape Matters: Plant Architecture Affects Chemical Uniformity in Large-Size Medical Cannabis Plants. Plants. 2021 Sep;10(9):1834. – https://www.mdpi.com/2223-7747/10/9/1834
[ii] Danziger N, Bernstein N. Plant architecture manipulation increases cannabinoid standardization in ‘drug-type medical cannabis. Industrial Crops and Products. 2021 Sep 1;167:113528. – https://www.sciencedirect.com/science/article/abs/pii/S0926669021002922