# Copper

> Copper (Cu) is a micronutrient used in photosynthetic electron transport and lignin formation; plants need only traces, and excess is toxic to roots.

- Canonical: https://genetixbay.com/knowledge/glossary/copper.html
- Also written: Cu, Cu2+, copper deficiency, copper toxicity
- Glossary category: Nutrients · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

Copper is a [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) absorbed as Cu2+. It is part of plastocyanin, which carries electrons in [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), and of enzymes involved in lignin synthesis and oxidative defence. Plants need very little, and it is largely immobile.

## In practice

[Deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) is rare in mineral feeds. When it occurs, new leaves may be dark or bluish, twisted, with wilting or dying tips and weak stems. [Toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md) is the more realistic risk: copper pipes, copper-based ionisers, copper fungicide residues or overdosing can damage roots and induce [iron deficiency](https://genetixbay.com/knowledge/glossary/iron.md). Hydro feeds usually carry only about 0.03-0.1 mg/L (ppm) Cu.

## Don't confuse with

- **Copper fungicides**: a pest-control use, not a nutrition strategy.
- **Zinc deficiency**: also twists new growth, but with [short internodes](https://genetixbay.com/knowledge/glossary/node-stacking.md).
- **Heat stress**: tip curl without a nutrient cause.

## Myth check

Copper is sometimes added to reservoirs as a "root protectant". At the doses that suppress pathogens it can also injure roots; treat claims with caution. See [root browning in hydro](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md).

## Related terms

[Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Copper sulfate](https://genetixbay.com/knowledge/glossary/copper-sulfate.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md), [Immobile nutrient](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md), [Chelate](https://genetixbay.com/knowledge/glossary/chelate.md)

## Read more

- [Copper (Cu) in cannabis: limp, distorted new growth and root-burning excess](https://genetixbay.com/knowledge/nutrients/copper.md)

## Sources

1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9
2. 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