Elevating nutrient input is often thought to increase the yield and cannabinoid concentration of medical cannabis.
However, increased legalization has raised awareness about the environmental impact of overfertilization, with elevated levels of phosphorus (P) being of particular concern. In this study, researchers report the effects of increasing P above levels adequate for other crops (15, 30, 45, 60, or 90 mg per L) and examine the interactive effects of elevated P with elevated nutrient solution concentration (measured as electrical conductivity; 2 and 4 mS per cm). The researchers utilized closed-system hydroponics to continuously monitor root zone nutrient concentrations. The concentration of P in leaf tissue doubled, and flower P concentration increased by 70% when P input rose from 15 to 90 mg per L. However, there was no difference in yield or quality among treatments. Doubling nutrient input from 2 to 4 mS per cm increased nutrient accumulation in the solution but did not significantly enhance yield or quality. Reducing P in the refill solution from 90 to 15 mg per L decreased P in the solution at harvest from 300 to less than 0.1 mg per L. Despite the low steady-state concentration of P in the solution in the 15 mg per L treatment, there was no difference in yield or quality among treatments, regardless of the concentration of other elements. Despite the high nutrient concentrations in the root zone solution, there was no leaf necrosis or other visual effects among treatments.
These data indicate that cannabis tolerates high nutrient concentrations, but neither excessive P nor excessive fertilization improves yield or quality.
(2025). Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science. 16. 10.3389/fpls.2025.1433985.
Source: Research Gate