Tad Hussey and Deron Caplan
Dec 3, 2019
Published Research on Cannabis with Dr. Deron Caplan
In this interview Deron explains his peer-reviewed cannabis research, covering fertilizer rates, substrates, propagation, and stress responses. The findings highlight both practical applications and the limits of generalizing results across systems.
Fertilizer & Substrate Research
Trials tested cannabis grown in coco coir substrates with varying container capacities (wetter vs. drier media).
Plants tolerated both conditions in the vegetative stage, but in flowering, drier substrates produced larger plants and 11–13% higher yields.
Cannabis required relatively high organic fertilizer rates compared to crops like tomatoes. However, excessive fertilization reduced cannabinoid yields due to salinity stress.
Contrary to common assumptions, plants tolerated a wide pH range (5.1–7.4) without visible nutrient deficiencies.
Cannabinoid Response to Fertilization
Yield increased with higher fertilizer rates up to a point, then plateaued.
Excessive fertilization diluted cannabinoids such as THC, THCA, and CBGA per plant, even if biomass increased.
This showed that “more fertilizer” does not always equal stronger flower, underscoring the importance of optimizing—not maximizing—nutrient levels.
Propagation (Cloning) Research
Cutting leaf tips, a common grower practice, reduced rooting success by ~20%. Wounding leaves decreases photosynthetic area and increases pathogen entry points.
Using fewer intact leaves is a better strategy than cutting tips to reduce leaf area in dense propagation domes.
Rooting success did not depend on whether cuttings were taken from the top (apical) or bottom (basal) of mother plants, challenging another widely held belief.
Conventional IBA rooting hormone significantly outperformed the organic willow extract tested, though the door remains open for future organic solutions.
Stress Response Trials
Deron tested controlled drought stress in late flowering. Using specialized sensors, he tracked plant water status and correlated it with visible signs like wilting and leaf angle.
Applied at week 7 of a 9-week cycle, drought stress did not reduce yield but increased cannabinoid content: THCA rose 12%, CBDA 13%, with even higher gains in cannabinoid yield per plant (up to ~47%).
Stress works because plants perceive accumulated strain over time, but outcomes vary by substrate and environment. Simply “letting plants wilt” is risky and not universally beneficial.
Takeaways for Growers
Cannabis is a relatively high feeder but must be kept within optimal fertilizer ranges.
Drier flowering substrates or more frequent irrigation cycles can boost yield.
Cutting clone leaf tips is counterproductive; remove full leaves if necessary.
Drought stress, if carefully timed and applied, can raise cannabinoid concentrations without lowering harvest weight.
Most importantly: controlled science often contradicts long-held cultivation myths.