# Nickel (Ni) in cannabis: essential, needed in traces, almost never worth adding

> Nickel became the most recently accepted essential plant micronutrient in 1987; its known job is activating urease, the enzyme that breaks down urea. Requirements are so small that contamination in salts, water and media normally covers them, and there is no published evidence of nickel deficiency in cannabis. Do not add nickel unless you feed urea in a very pure system; excess nickel is toxic and cannabis is known to accumulate metals.

- Canonical: https://genetixbay.com/knowledge/nutrients/nickel.html
- Category: Nutrients · Level: Advanced
- Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Any stage · 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

**Does cannabis need nickel?** Cannabis, like all higher plants, needs nickel as an essential [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), but only in traces. Nickel was accepted as essential in 1987, after barley grown for three generations without it failed to produce viable grain. Contamination in fertiliser salts, water and media normally covers the requirement, and no nickel deficiency has been published in cannabis.

**Should I add nickel to my hydroponic nutrients?** No, you should not add nickel to normal cannabis hydroponic nutrients; the added amount should be 0 mg/L because impurities in salts and water already cover the tiny requirement. The only exception is feeding urea in an unusually pure system, and switching to nitrate nitrogen avoids that need entirely. Excess nickel is toxic and cannabis accumulates metals.

**What does nickel do in plants?** Nickel's known job in plants is activating urease, the enzyme that breaks urea down into [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md). Without it, urea from fertiliser and from the plant's own nitrogen recycling builds up in leaves to toxic levels and can cause tip necrosis in sensitive species. Nickel is mobile in the phloem and moves into seeds, which is why [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) affected barley seed viability.

**Can urea fertilizer cause leaf [tip burn](https://genetixbay.com/knowledge/glossary/nutrient-burn.md) without nickel?** In nickel-deficient plants, urea can accumulate and cause leaf tip and margin necrosis, because urease needs nickel to break urea down. This has been documented in other crops but not in cannabis. For tip burn on a urea-containing feed, first rule out [overfeeding](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md), high [EC](https://genetixbay.com/knowledge/glossary/ec.md), ammonium toxicity and potassium shortage; nickel is the last suspect.

**Is nickel toxic to cannabis?** Excess nickel is toxic to plants, causing interveinal chlorosis that resembles [iron deficiency](https://genetixbay.com/knowledge/glossary/iron.md), because nickel competes with iron, plus stunted roots and growth. Cannabis and hemp accumulate [heavy metals](https://genetixbay.com/knowledge/glossary/heavy-metals-panel.md) from contaminated soils, which is a reason to keep nickel out. If you suspect toxicity, test water and soil, remove the source, and in soil raise [pH](https://genetixbay.com/knowledge/glossary/ph.md) to reduce availability.

**Short answer.** Nickel is a genuine essential micronutrient: Brown, Welch and Cary showed in 1987 that barley grown for three generations in Ni-depleted conditions failed to produce viable grain [1]. Its known role is activating urease, which breaks urea into ammonium [2]. The requirement is so small that contamination in fertiliser salts, water and media normally covers it. There is no published report of nickel deficiency in cannabis. Do not add nickel unless you feed urea in an unusually pure system.

## What's happening

Ni is the metal centre of urease. Without it, urea (from urea fertiliser and from the plant's own nitrogen recycling) builds up in leaves to toxic levels and causes tip necrosis in sensitive species [2]. Ni is mobile in the phloem and moves into seeds [2].

The amount needed is in the range of tens to a few hundred micrograms per kilogram of leaf [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) [1][2]. Ordinary reagent and fertiliser-grade salts carry more than enough as impurities; that is also why Ni went unrecognised for so long (Epstein made the same point about contaminants and [silicon](https://genetixbay.com/knowledge/glossary/silicon.md) [3]).

## How to recognise it

- **Deficiency (other crops):** leaf tip and margin necrosis linked to urea accumulation; in barley, failure of seed viability [1][2]. Not documented in cannabis.
- **Toxicity:** interveinal chlorosis similar to iron deficiency (Ni competes with Fe), stunted roots and growth [2]. Cannabis and hemp are effective accumulators of heavy metals from contaminated soils, which is a reason to keep Ni out of the flower, not add more.

## Numbers that matter

| Parameter | Target | Conditions / notes |
|---|---|---|
| Solution Ni (added) | 0 mg/L for normal feeds | Contaminants suffice; *grower practice* and greenhouse standards |
| Solution Ni, if feeding urea in ultra-pure systems | ≤0.01–0.05 mg/L | |
| Leaf Ni, sufficiency | ~0.01–0.1 mg/kg range | Order of magnitude from crop literature [1][2] |
| Leaf Ni, toxicity in sensitive plants | >10 mg/kg | [2] |

## What to check first

- Tip burn on a urea-containing feed: first rule out overfeeding, high EC, ammonium toxicity and K shortage. Ni is the last suspect.
- Suspected Ni toxicity: test water and soil (industrial sites, some biosolids, stainless or plated fittings in poor condition).

## How to fix it

- **Deficiency (rare):** switch from urea to nitrate-based N, which sidesteps urease entirely. If you must use urea, a trace of nickel [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md) hexahydrate (≈22% Ni) in the micronutrient stock.
- **Toxicity:** remove the source; in soil, raising pH reduces Ni availability [2].
- **Safety:** nickel salts are skin sensitisers and suspected carcinogens; gloves, no dust.

## Common mistakes

- Adding "complete" trace-element products with Ni to an already complete feed for no reason.
- Assuming essential means "must be supplemented".

## Evidence

- Ni is essential for higher plants: *Established* [1][2].
- Contaminant Ni covers needs in practice: *Supported* (agronomy consensus [2]); no cannabis study.
- Benefit of Ni supplementation in cannabis: *No evidence*.

## Sources

1. Brown PH, Welch RM, Cary EE. 1987. Nickel: a micronutrient essential for higher plants. Plant Physiology 85(3):801-803. https://doi.org/10.1104/pp.85.3.801
2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9
3. Epstein E. 1994. The anomaly of silicon in plant biology. PNAS 91(1):11-17. https://doi.org/10.1073/pnas.91.1.11