# Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets

> Nitrogen drives leaf growth and photosynthesis. Cannabis does best on mostly nitrate N (about 150–200 mg/L in soilless veg and early flower), with ammonium kept at or below about 10–30% of total N; above 30% ammonium, cannabis trials show toxicity and lost yield. Deficiency yellows the oldest leaves first; excess gives dark, clawed leaves and soft, leafy growth.

- Canonical: https://genetixbay.com/knowledge/nutrients/nitrogen.html
- Category: Nutrients · Level: Intermediate
- Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Seedling, Veg, Transition, Flower, Ripening · Systems: Any system
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**How much nitrogen does cannabis need in veg and flower?** Cannabis needs roughly 160 mg/L nitrogen in veg, the optimum in a controlled pot trial where 30 mg/L was deficient and 240-320 mg/L was no better. In flower, a mineral DWC trial predicted a yield optimum near 194 mg/L. Liquid organic feeds in coir needed more on paper, about 212-261 mg/L, because organic nitrogen is less available.

**Nitrate or ammonium for cannabis?** Cannabis does best on mostly nitrate nitrogen, with ammonium kept at or below about 10-30% of total nitrogen. Nitrate uptake makes the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) pH rise, while ammonium uptake releases protons and drops pH. In a controlled trial, [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) were highest under pure nitrate, and 10-30% ammonium did not substantially harm secondary metabolism.

**Why are my bottom leaves turning yellow?** Bottom cannabis leaves turning evenly pale yellow, with the fade climbing upward, is the classic sign of nitrogen deficiency, because nitrogen is mobile and the plant strips old leaves to feed new growth. Check the stage first: a slow bottom-up fade in the last 2-3 weeks of flower is normal senescence. Also rule out [overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md), cold solution, root rot and pH.

**What does nitrogen toxicity look like? Dark green clawed leaves?** Yes, nitrogen excess in cannabis typically shows as very dark green, glossy leaves with tips hooking down, called the claw, plus thin, soft stems and delayed or leafy flowering. Ammonium toxicity adds root browning, leaf-margin necrosis and signs of calcium, magnesium and potassium shortage. Claw can also come from overwatering, heat or pH, so check those too.

**How many ppm N in a hydro nutrient solution?** A cannabis hydro nutrient solution typically carries about 150-200 ppm (mg/L) nitrogen in veg and early flower, mostly as nitrate. Seedlings and fresh clones get about 50-100 ppm at low EC of 0.6-1.0 mS/cm, as grower practice. Healthy recent mature leaves should test 3.3-5.0% nitrogen by [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md); around 1.6% marks first deficiency symptoms.

**Is ammonium bad for cannabis?** Ammonium is harmful to cannabis above about 30% of total nitrogen. In a controlled trial at 200 mg/L nitrogen, yield fell 46% as ammonium rose from 0 to 50%, plants at 50% showed toxicity, and plants at 100% died. Small amounts are fine: commercial [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md) carries about 1% ammonium-N, so avoid fixing deficiencies with ammonium sulfate or urea in hydro.

**Does lower nitrogen raise THC percentage?** Research shows lower nitrogen in flower can raise cannabinoid and terpene percentage while lowering total yield: in one controlled trial, concentrations were suppressed at higher nitrogen while inflorescence yield rose with nitrogen up to about 160 mg/L. It is a trade-off to set deliberately in the flower recipe, not a reason to flush, which starves the plant and is a myth.

**How do I taper nitrogen before harvest?** To taper nitrogen before harvest, cut it over the last 3-4 weeks: about 75% of normal late-flower nitrogen at week minus 3, 50% at minus 2, 25% at minus 1 and 0-20 mg/L in the final days. Keep phosphorus, potassium, calcium, magnesium, sulfur and micros unchanged, using single salts or [per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md). This is GenetixBay grower practice, not yet trial-tested.

**Short answer.** Nitrogen is the engine of leaf growth. In soilless and hydro systems cannabis does well on roughly 150–200 mg/L N, supplied mostly as nitrate (NO₃⁻), with ammonium (NH₄⁺) capped at about 10–30% of total N [1][2][3]. Too little N yellows the oldest leaves first and cuts yield hard; too much gives dark, glossy, clawed leaves and soft, leafy growth. Ammonium above about 30% of total N caused toxicity in a controlled cannabis trial, and 100% ammonium killed the plants [2].

## What's happening

N is part of every amino acid, protein, nucleic acid and chlorophyll molecule. Plants take it up as nitrate or ammonium.

- **Nitrate** is the safe workhorse. Its uptake makes roots release hydroxide or bicarbonate, so the root zone **pH rises** on a nitrate feed (see [pH drift](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md)).
- **Ammonium** is taken up fast and assimilated in the roots, which costs sugars. Its uptake releases protons, so the root zone **pH falls**. In excess it is toxic: it competes with K⁺, Ca²⁺ and Mg²⁺ for uptake and can damage roots [2].

In the Saloner and Bernstein NH₄/NO₃ trial (uniform 200 mg/L N, 0–100% ammonium), yield fell 46% as ammonium went from 0 to 50%, plants at 50% showed toxicity, and plants at 100% died. Cannabinoids were highest under pure nitrate; 10–30% ammonium did not substantially harm secondary metabolism, and the authors advise against ratios above 30% NH₄ [2].

### The nitrogen and potency trade-off

In flower, Saloner and Bernstein found that cannabinoid and terpenoid concentrations were suppressed at higher N supply, while inflorescence yield rose with N up to about 160 mg/L [8]. So lower N can raise cannabinoid and terpene **percentage** while lowering **total yield**. It's a trade-off to set deliberately with your flower recipe, not a reason to flush: a pre-harvest flush starves the plant while it is packing on yield and resin, and is a *Myth* (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)).

### Late-flower N taper (instead of flushing)

GenetixBay tapers N in the last 3–4 weeks, towards zero at the finish, and keeps P, K, Ca, Mg, S and the micros at normal late-flower strength. It puts the trade-off above to deliberate use: a little potency percentage for a little bulk, with the plant otherwise fully fed. *Grower practice*, widely recommended by experienced growers; this ramp hasn't been tested in a controlled trial.

| Weeks before harvest | N (mg/L) | Everything else |
|---|---|---|
| −4 | 100–150 (normal late flower) | Full late-flower feed |
| −3 | ~75–110 (about 75 %) | P, K, Ca, Mg, S and micros unchanged |
| −2 | ~50–75 (about 50 %) | Unchanged |
| −1 | ~25–40 (about 25 %) | Unchanged |
| Final days | 0–20 | Unchanged; keep normal runoff |

To do it you need per-element control: single salts with an N-free Ca source (see [hydroponic salts](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md)) or a per-element dosing controller. Diluting a 2-part cuts everything, not just N.

N is **mobile** in the phloem. When supply falls short, the plant strips old leaves to feed new ones, so deficiency starts at the bottom (see [mobile vs immobile nutrients](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md)).

## How to recognise it

**Deficiency.** Slight stunting, then even pale-yellowing of the lower foliage that climbs upward; advanced leaves go fully yellow, necrotic and drop [4]. In DWC flower trials, N deficiency appeared in flower week 3 at the lower fan-leaf tips, spread upward, [fan leaves](https://genetixbay.com/knowledge/glossary/fan-leaf.md) senesced by week 5, and inflorescence [fresh weight](https://genetixbay.com/knowledge/glossary/wet-weight.md) was about 72% lower than control [5]. Red or purple petioles often accompany it, but that alone is not diagnostic (genetics and cold do it too).

**Excess (and ammonium toxicity).** Very dark green, glossy leaves; leaf tips that hook down ("the claw"); thin, soft stems; delayed or leafy flowering. Ammonium toxicity adds root browning, leaf-margin necrosis and symptoms of Ca/Mg/K shortage because ammonium blocks their uptake [2]. Claw also has other causes (overwatering, heat, pH), so see [taco and canoeing leaves](https://genetixbay.com/knowledge/diagnosis/taco-canoeing-leaves.md).

## Numbers that matter

| Parameter | Target | Conditions / notes |
|---|---|---|
| Solution N, seedlings and fresh clones | 50–100 mg/L | *Grower practice*; low EC (0.6–1.0 mS/cm) |
| Solution N, veg | ~160 mg/L optimum; 150–200 mg/L working range | Pot trial, long photoperiod; 30 mg/L deficient, 240–320 mg/L no better [1] |
| Solution N, flower (mineral, DWC) | ~194 mg/L predicted optimum for yield | Response-surface trial, one high-THC cultivar [3] |
| Solution N, flower (liquid organic, coir) | 212–261 mg/L N | Organic N is less available; one substrate [6] |
| NH₄⁺ share of total N | ≤10–30% | >30% risks toxicity; 50% cut yield 46% [2] |
| Leaf N, healthy (most recent mature leaf) | 3.3–5.0% dry weight | NC State floral hemp range [7] |
| Leaf N at first deficiency symptoms | ~1.6% | Cannabis, sand culture [4] |

## What to check first

1. **Stage.** A slow bottom-up fade in the last 2–3 weeks of flower is normal senescence, not a problem to fix.
2. **Root zone.** Overwatering, cold solution (<18 °C / 64 °F), root rot or [root aphids](https://genetixbay.com/knowledge/glossary/root-aphid.md) cause "N deficiency" in a well-fed plant. Check roots before the feed (see [root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md)).
3. **pH.** Outside about 5.5–6.5 in soilless, uptake of several nutrients suffers.
4. **[EC in](https://genetixbay.com/knowledge/glossary/input-ec.md) and out.** Low input EC means real hunger; high runoff EC means salts or poor uptake.
5. **Feed history.** A "bloom" base with very low N switched on at flip is a classic cause of early-flower yellowing.

## How to fix it

- **Mineral hydro/coco:** raise N by 10–20% (for example 150 → 170 mg/L), using calcium nitrate or [potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md). Do not double it.
- **Keep ammonium modest.** Most commercial calcium nitrate contains about 1% ammonium-N (5–8% of its N); that is fine. Do not "fix" a deficiency with ammonium sulfate or urea in hydro.
- **Soil/organic:** liquid organic N or a top-dress (blood meal, feather meal, fish hydrolysate) at label rate; expect 1–2 weeks before response because microbes must mineralise it.
- **Toxicity:** cut N 20–30%, feed at lower EC for one or two cycles, check runoff EC. If ammonium-based, switch to a nitrate-dominant feed and raise root-zone pH back into range.

## How to confirm it worked

- Yellowing stops climbing within 5–7 days; already-yellow leaves stay yellow.
- New leaves come in mid-green. For excess, new leaves stop clawing within about a week.
- If you can, a [tissue test](https://genetixbay.com/knowledge/glossary/tissue-test.md) on the most recent mature leaf lands at 3.3–5.0% N [7].

## Common mistakes

- Feeding more N to a plant with sick roots.
- Treating harvest-time fade as a deficiency.
- Running high-ammonium "organic-style" salts in DWC and then chasing a falling pH.
- Assuming dark green always means healthy.

## Evidence

- Bottom-up yellowing as the N deficiency signature in cannabis: *Established* (two controlled studies in different systems [4][5]).
- Veg optimum near 160 mg/L N and flower optimum near 190–200 mg/L N in mineral feeds: *Supported* (single-cultivar trials [1][3]); organic feeds need higher N because availability is lower [6].
- Ammonium above ~30% of N harms cannabis: *Supported* (one rigorous trial, consistent with other crops [2]).
- Purple petioles as a reliable N sign: *Contested*.
- Lower N in flower raising cannabinoid and terpene percentage while lowering yield: *Supported* (one controlled trial [8]); a trade-off, not a reason to flush.
- Tapering N towards zero over the last 3–4 weeks while feeding everything else: *Grower practice* (GenetixBay house approach).

## Sources

1. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516
2. Saloner A, Bernstein N. 2020. Response of medical cannabis (Cannabis sativa L.) to nitrogen supply under long photoperiod. Frontiers in Plant Science 11:572293. https://doi.org/10.3389/fpls.2020.572293
3. Saloner A, Bernstein N. 2022. Nitrogen source matters: high NH4/NO3 ratio reduces cannabinoids, terpenoids, and yield in medical cannabis. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224
4. Bevan L, Jones M, Zheng Y. 2021. Optimisation of nitrogen, phosphorus, and potassium for soilless production of Cannabis sativa in the flowering stage using response surface analysis. Frontiers in Plant Science 12:764103. https://doi.org/10.3389/fpls.2021.764103
5. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432
6. Llewellyn D, Golem S, Jones AMP, Zheng Y. 2023. Foliar symptomology, nutrient content, yield, and secondary metabolite variability of cannabis grown hydroponically with different single-element nutrient deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422
7. Caplan D, Dixon M, Zheng Y. 2017. Optimal rate of organic fertilizer during the flowering stage for cannabis grown in two coir-based substrates. HortScience 52(12):1796-1803. https://doi.org/10.21273/HORTSCI12401-17
8. Suchoff D, McGinnis M, Davis J, Whipker B, Hicks K. 2026. Hemp leaf tissue nutrient ranges: refinement of reference standards for floral hemp. NC State Extension AG-904. https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges