Most nutrient advice comes from fertilizer companies or grower tradition. Since legalization, researchers have started measuring cannabis nutrient needs directly, often in hydroponic systems where every input can be controlled.
In flowering, a deep-water-culture study found yield peaked around 194 mg/L nitrogen and 59 mg/L phosphorus, with potassium making no difference in the range tested. A vegetative-stage study recommended roughly 160–200 mg/L nitrogen, 30 mg/L phosphorus and 60 mg/L potassium. The form of nitrogen matters too: supplying a large share as ammonium instead of nitrate cut yield by up to 46%.
A recurring theme is a trade-off between bulk and concentration. Feeding more organic fertilizer in flower increased yield but diluted THC and related cannabinoids, and deliberately feeding less in flower lowered yield while raising CBD concentration.
Treat these numbers as study-specific. They come from particular cultivars, systems and fertilizers, and they don’t convert directly into a feeding chart for soil or coco.
Gaps we’re still filling: peer-reviewed tests of pre-harvest flushing, pH targets and EC.
Key terms
mg/L
Milligrams per liter, a measure of nutrient concentration in water. In dilute nutrient solutions, 1 mg/L is about 1 ppm.
THCA and THC
Living cannabis makes THCA, an acid form. Heat and time convert it to THC. CBDA and CBD work the same way.
Studies
6 studies
Mineral nutrition for Cannabis sativa in the vegetative stage using response surface analysis
Frontiers in Plant Science · 2024
Cannabis (type not specified)
Controlled experiment
Open access
Recommended vegetative feed: about 160–200 mg/L nitrogen, 30 mg/L phosphorus and 60 mg/L potassium.
Authors: Patrick Yawo Kpai, Oluwafemi Adaramola, Philip Wiredu Addo, Sarah MacPherson, Mark Lefsrud
15:1501484
Study plant: Cannabis in a hydroponic system, vegetative stage only
Using the same response-surface approach as earlier flowering-stage work, McGill University researchers varied nitrogen, phosphorus and potassium for vegetative cannabis in a hydroponic system. Nutrient interactions mattered: the effect of one nutrient depended on the levels of the others. Balancing growth against nutrient-use efficiency, they recommend about 160–200 mg/L nitrogen, 30 mg/L phosphorus and 60 mg/L potassium for the vegetative stage.
Cannabis Hunger Games: nutrient stress induction in flowering stage – impact of organic and mineral fertilizer levels on biomass, cannabidiol (CBD) yield and nutrient use efficiency
Frontiers in Plant Science · 2023
Drug-type cannabis
Controlled experiment
Open access
One-third less fertilizer still delivered 95% of the CBD yield.
Authors: Danilo Crispim Massuela, Sebastian Munz, Jens Hartung, P. M. Nkebiwe, Simone Graeff-Hönninger
14:1233232
Study plant: CBD-dominant medicinal cannabis grown indoors
CBD-dominant medicinal cannabis was flowered on mineral or organic fertilizer at three strengths (80, 160 and 240 mg/L nitrogen) to test whether deliberately underfeeding in flower can save fertilizer. Underfed plants yielded less flower, but higher CBD concentrations made up most of the difference: they reached 95% of the CBD yield with one-third less fertilizer. The organic fertilizer was taken up and used less efficiently than the mineral one.
Nitrogen Source Matters: High NH4/NO3 Ratio Reduces Cannabinoids, Terpenoids, and Yield in Medical Cannabis
Frontiers in Plant Science · 2022
Drug-type cannabis
Controlled experiment
Open access
High-ammonium feeding cut flower yield by up to 46%; moderate ammonium (10–30%) was fine.
Authors: Avia Saloner, Nirit Bernstein
13:830224
Study plant: Medical drug-type cannabis fed 200 mg/L nitrogen in five ammonium/nitrate ratios
Medical cannabis was fed the same total nitrogen (200 mg/L) supplied in five ratios of ammonium to nitrate, from 0% to 100% ammonium. Raising the ammonium share generally hurt the plants: flower yield, cannabinoids, terpenes and photosynthesis were highest on nitrate alone, and yield fell 46% as ammonium rose from 0% to 50%. Moderate ammonium levels (10–30%) caused little harm.
Optimisation of Nitrogen, Phosphorus, and Potassium for Soilless Production of Cannabis sativa in the Flowering Stage Using Response Surface Analysis
Frontiers in Plant Science · 2021
Drug-type cannabis
Controlled experiment
Open access
Best flower yield at about 194 mg/L nitrogen and 59 mg/L phosphorus; potassium level didn’t matter in the range tested.
Authors: Lewys Bevan, Max Jones, Youbin Zheng
12:764103
Study plant: One high-THC cultivar in deep-water culture
A high-THC cultivar was flowered in deep-water culture across combinations of nitrogen (70–290 mg/L), phosphorus (20–100 mg/L) and potassium (60–340 mg/L). Flower yield peaked at about 194 mg/L nitrogen and 59 mg/L phosphorus, with more or less of either lowering yield. Potassium had no measurable effect on yield across the range tested.
Optimal Rate of Organic Fertilizer during the Vegetative-stage for Cannabis Grown in Two Coir-based Substrates
HortScience · 2017
Drug-type cannabis
Controlled experiment
In coir, a vegetative organic feed supplying about 389 mg/L nitrogen gave the best results.
Authors: Deron Caplan, Mike Dixon, Youbin Zheng
52(9):1307–1312
Study plant: Medical drug-type cannabis in two commercial coir mixes, walk-in growth chamber
Plants were fed a liquid organic fertilizer (4.0-1.3-1.7) at five rates during vegetative growth in two coir-based mixes that differed in how much water they hold. The two coir mixes performed the same. Yield, cannabinoid content and growth were best at a rate supplying about 389 mg/L nitrogen during veg, which gave 1.8 times the yield of the lowest rate.
Optimal Rate of Organic Fertilizer during the Flowering Stage for Cannabis Grown in Two Coir-based Substrates
HortScience · 2017
Drug-type cannabis
Controlled experiment
More organic feed in flower meant more bud but lower cannabinoid concentration.
Authors: Deron Caplan, Mike Dixon, Youbin Zheng
52(12):1796–1803
Study plant: Medical cultivar ‘WP:Med (Wappa)’ in two commercial coir mixes, walk-in growth chamber
In this follow-up flowering trial, a liquid organic fertilizer (2.0-0.87-3.32) was applied at five rates to plants in two coir mixes. Feeding more increased growth and yield but diluted THC, THCA and CBGA concentrations. In the drier of the two coir mixes, rates supplying 212–261 mg/L nitrogen best balanced flower yield against cannabinoid yield.