# Copper sulfate

> Copper sulfate pentahydrate (CuSO4·5H2O), about 25.5% copper, supplies trace copper in micronutrient mixes and is toxic to roots in excess.

- Canonical: https://genetixbay.com/knowledge/glossary/copper-sulfate.html
- Also written: CuSO4, copper sulphate, blue vitriol, bluestone, CuSO4·5H2O
- 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 sulfate is the bright blue salt of [copper](https://genetixbay.com/knowledge/glossary/copper.md) and [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md), normally sold as the pentahydrate (CuSO4·5H2O) at about 25.5% Cu. It is soluble and also widely used as a fungicide and algicide.

## In practice

In a [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) stock, copper is needed at very low levels, about 0.03-0.1 mg/L (ppm) in the final feed. That is only a fraction of a milligram of salt per litre, so it is always dosed from a concentrated stock. Overdosing damages roots and can induce [iron deficiency](https://genetixbay.com/knowledge/glossary/iron.md). Garden-store copper sulfate sold for algae control may not be pure enough for nutrition; check the grade.

## Units and formula

1 mg/L of the pentahydrate gives about 0.255 mg/L (ppm) Cu.

## Don't confuse with

- **Bordeaux mixture**: copper sulfate plus lime, a fungicide spray.
- **Copper chelate (Cu-EDTA)**: more stable at higher [pH](https://genetixbay.com/knowledge/glossary/ph.md).
- **Copper ionisers**: devices that release copper into water, a contamination risk in hydro.

## Related terms

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

## Read more

- [Copper (Cu) in cannabis: limp, distorted new growth and root-burning excess](https://genetixbay.com/knowledge/nutrients/copper.md)
- [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md)

## Sources

1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6