When to harvest and how to trim are decisions every grower makes, usually by eye. The research so far is limited but practical.
In a CBD-type genotype, flower weight kept increasing through week 11 of flowering while CBD concentration stayed flat, so total CBD yield peaked at week 9. Top buds had higher CBD than middle or lower buds.
Trimming involves a trade-off. In one medical chemovar, a light trim before drying produced the highest cannabinoid levels, while trimming after drying kept the most terpenes. A pre-harvest hexanoic acid spray raised some cannabinoids and terpenes and helped them last through storage, though it is an experimental treatment, not a standard grower product.
Gaps we’re still filling: peer-reviewed tests of trichome color as a harvest signal, and harvest windows for THC-dominant cultivars.
Key terms
Chemovar
A chemical variety: plants grouped by their cannabinoid and terpene profile rather than by strain name.
Terpenes
Aromatic compounds that give cannabis its smell and flavor. Monoterpenes (like myrcene and limonene) are lighter and more volatile than sesquiterpenes (like beta-caryophyllene).
Studies
3 studies
Optimization of Trimming Techniques for Enhancing Cannabinoid and Terpene Content in Medical Cannabis Inflorescences
Medical Cannabis and Cannabinoids · 2024
Drug-type cannabis
Controlled experiment
Open access
A light wet trim maximized cannabinoids; trimming after drying kept the most terpenes.
Authors: Nimrod Brikenstein, Matan Birenboim, David Kenigsbuch, Jakob A. Shimshoni
7(1):111–118
Study plant: One commercial medical hybrid chemovar (Gen12)
Using a commercial hybrid chemovar (Gen12), the researchers compared trimming before versus after drying, and light versus aggressive trimming before drying, then measured cannabinoids and terpenes. A light trim before drying gave the highest cannabinoid concentrations, while trimming after drying preserved the most terpenes. All buds were dried under the same controlled conditions identified in the team’s earlier drying research.
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.
Improved Long-Term Preservation of Cannabis Inflorescence by Utilizing Integrated Pre-Harvest Hexanoic Acid Treatment and Optimal Post-Harvest Storage Conditions
Plants · 2024
Drug-type cannabis
Controlled experiment
Open access
THCA fell 4–23% over four months; a pre-harvest spray plus vacuum storage kept losses lowest.
Authors: Matan Birenboim, Daniel Chalupowicz, David Kenigsbuch, Jakob A. Shimshoni
13(7):992
Study plant: One high-THCA chemovar, stored for four months after harvest
A high-THCA chemovar was sprayed with hexanoic acid before harvest (or left untreated), then dried, cured and stored for four months with or without vacuum sealing. THCA fell by 4–23% during storage, with the smallest loss in plants that received both the pre-harvest spray and vacuum storage. The spray protected monoterpenes more than vacuum storage alone, and treated plants had higher levels of some cannabinoids at harvest.