Higher nitrogen fertilization increased leaf biomass but actually decreased cannabinoid concentrations and per-plant yield in a CBD-type cannabis cultivar, while pruning had no significant effect.
Read this if you grow cannabis commercially or are interested in optimizing cannabinoid production through cultivation practices.
60-210 mg/LOptimal nitrogen range for maximizing cannabinoid yield in CBD-type cannabis
What the researchers found
In a controlled-environment study of a CBD-type Cannabis sativa, increasing nitrogen supply from 60 to 500 mg/L significantly increased leaf biomass but decreased both cannabinoid concentration and total cannabinoid yield per plant. Double stem pruning did not increase cannabinoid concentrations or affect biomass. An incidental finding was that plants on the greenhouse edge with more sunlight developed more biomass and higher cannabinoid concentrations. The optimal nitrogen range appeared to be between 60 and 210 mg/L.
Why it matters
For commercial cannabis growers, this study challenges the intuition that more fertilizer equals more product. Over-fertilizing with nitrogen is not only wasteful but actively counterproductive for cannabinoid production.
The numbers in context
- Nitrogen rates tested: 30, 60, 210, 500 mg/L
- 5 weeks vegetative growth under 210 mg/L N
- 12 weeks flowering under treatment nitrogen rates
- Light regime: 18h (veg) then 12h (flower)
- Optimal N range: 60-210 mg/L
- Pruning treatment: double stem pruning (no significant effect)
How the study worked
Controlled-environment glasshouse study. Clones of a CBD-type Cannabis sativa grown in pots with coarse sand. Four nitrogen levels applied during 12-week flowering phase. Double stem pruning as additional treatment. Measured biomass, nitrogen concentration, and cannabinoid concentration at final harvest.
Who was studied
CBD-type Cannabis sativa clones in controlled glasshouse conditions
What this study cannot tell us
Single cultivar study — results may differ across cannabis varieties. Controlled greenhouse environment may not reflect field conditions. The sunlight edge effect was incidental, not a controlled variable. Specific cannabinoid concentrations and yields are not provided in the abstract.
How to read the evidence
Controlled greenhouse experiment with a single cultivar. Provides useful agronomic data but limited generalizability across varieties and growing conditions.
When this study was published
Published in 2023. Addresses practical cultivation questions for the legal cannabis industry.
The bigger picture
As medicinal cannabis production scales up, understanding the relationship between agronomic inputs and cannabinoid output is essential for sustainable and efficient cultivation. This study adds to evidence that secondary metabolite production in cannabis follows different rules than simple biomass accumulation.
Questions still open
- Does the nitrogen-cannabinoid tradeoff differ for THC-dominant cultivars?
- Would supplemental lighting replicate the edge effect seen with sunlight?
- At what nitrogen level does cannabinoid yield per unit of fertilizer peak?
Read the original research
Investigating how nitrogen nutrition and pruning impacts on CBD and THC concentration and plant biomass of Cannabis sativa.
Scientific reports, 13(1), 19533
Citation
Dilena, Enrico; Close, Dugald C; Hunt, Ian; Garland, Sandra M. (2023). Investigating how nitrogen nutrition and pruning impacts on CBD and THC concentration and plant biomass of Cannabis sativa.. Scientific reports, 13(1), 19533. https://doi.org/10.1038/s41598-023-46369-5