Increasing Inflorescence Dry Weight and Cannabinoid Content in Medical Cannabis Using Controlled Drought Stress

Controlled application of drought can increase secondary metabolite concentrations in some essential oil-producing crops. To evaluate the effects of drought on cannabis (Cannabis sativa L.) inflorescence dry weight and cannabinoid content, drought stress was applied to container-grown cannabis plants through gradual growing substrate drying under controlled environment. Fertigation was withheld during week 7 in the flowering stage until midday plant water potential (WP) was approximately -1.5 MPa (drought stress threshold). This occurred after 11 days without fertigation. A well-irrigated control was used for comparison. Leaf net photosynthetic rate (P-n), plant WP, wilting (leaf angle), and volumetric moisture content (VMC) were monitored throughout the drying period until the day after the drought group was fertigated. At the drought stress threshold, P-n was 42% lower and plant WP was 50% lower in the drought group than the control. Upon harvest, drought-stressed plants had increased concentrations of major cannabinoids tetrahydrocannabinol acid (THCA) and cannabidiolic acid (CBDA) by 12% and 13%, respectively, compared with the control. Further, yield per unit growing area of THCA was 43% higher than the control, CBDA yield was 47% higher, Delta(9)-tetrahydrocannabinol (THC) yield was 50% higher, and cannabidiol (CBD) yield was 67% higher. Controlled drought stress may therefore be an effective horticultural management technique to maximize both inflorescence dry weight and cannabinoid yield in cannabis, although results may differ by cannabis cultivar or chemotype.