Topping, defoliation, lollipopping and plant spacing are some of the most debated techniques in cannabis growing. Controlled studies show that shaping the plant changes not just yield but how evenly cannabinoids are spread from the top of the plant to the bottom.
In large medical plants, pruning twice produced the highest cannabinoid yield per plant, while removing the primary branches drastically reduced it and defoliation alone didn’t raise it. Planting more densely raised yield per square meter but made potency less uniform through the canopy. In a CBD-type genotype, topped plants trended toward higher yields, and top buds carried more CBD than lower buds.
Bud position matters for quality: in two separate studies, upper buds tested higher in cannabinoids than lower ones. Techniques that bring more of the plant into strong light are a recurring theme.
Caveats: each of these studies used one cultivar, and large greenhouse plants may respond differently from small indoor plants in a tent.
Key terms
Chemovar
A chemical variety: plants grouped by their cannabinoid and terpene profile rather than by strain name.
Studies
3 studies
Too Dense or Not Too Dense: Higher Planting Density Reduces Cannabinoid Uniformity but Increases Yield/Area in Drug-Type Medical Cannabis
Frontiers in Plant Science · 2022
Drug-type cannabis
Controlled experiment
Open access
Two plants per square meter raised yield per area but made potency less uniform.
Authors: Nadav Danziger, Nirit Bernstein
13:713481
Study plant: One drug-type medical cultivar at 1 or 2 plants per square meter
A drug-type medical cultivar was grown at one or two plants per square meter, combined with four plant-architecture treatments. Denser planting increased yield per area but made cannabinoid concentrations less uniform across the plant, and spacing interacted with how the plants were shaped. The effect was cannabinoid-specific: some compounds varied more by bud position than others.
Shape Matters: Plant Architecture Affects Chemical Uniformity in Large-Size Medical Cannabis Plants
Plants · 2021
Drug-type cannabis
Controlled experiment
Open access
Pruning twice gave the highest cannabinoid yield per plant; removing primary branches crushed it.
Authors: Nadav Danziger, Nirit Bernstein
10(9):1834
Study plant: Large (about 2.5 m) CBD-dominant medical cannabis plants
Large medical cannabis plants (about 2.5 m tall) received eight shaping treatments, including defoliation, removing lower branches and leaves, removing branches, and pruning, to see which made cannabinoid levels more uniform from top to bottom. Pruning twice produced the highest cannabinoid yield per plant, while removing the primary branches cut it drastically. Defoliation alone did not raise cannabinoid yield.
Study plant: One CBD-dominant (chemotype III) medicinal genotype grown indoors
A CBD-dominant (chemotype III) genotype was harvested at four points between weeks 5 and 11 of flowering and grown with three pruning approaches: topping, removing side shoots, or no pruning. Flower weight kept increasing over time while CBD concentration stayed flat, so total CBD yield peaked at week 9. Top buds had higher CBD (9.9%) than middle (8.2%) or lower (7.7%) buds. Topped plants trended toward higher yields, though not significantly more than unpruned plants.