# Sulfate

> Sulfate (SO4 2-) is the form in which plants take up sulfur, delivered mainly by magnesium sulfate and potassium sulfate in mineral feeds.

- Canonical: https://genetixbay.com/knowledge/glossary/sulfate.html
- Also written: SO4, SO4 2-, sulphate, sulfate ion
- 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"

Sulfate is the doubly charged anion SO4 2-, the normal source of [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) for plant roots. Plants reduce it internally to build sulfur-containing amino acids and other compounds. Many fertiliser salts carry their metal partner as a sulfate, so sulfate often enters a feed as a passenger.

## In practice

[Magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md), [potassium sulfate](https://genetixbay.com/knowledge/glossary/potassium-sulfate.md) and the [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) sulfates ([manganese](https://genetixbay.com/knowledge/glossary/manganese.md), zinc, copper) all add sulfate. Calcium sulfate (gypsum) is only sparingly soluble, so concentrated calcium and sulfate stocks precipitate together. That is one of the two main reasons mineral feeds are split into [A and B](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) parts. In the final dilute solution they coexist without trouble. [Tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) can also contribute meaningful sulfate; a water report will show it.

## Units and formula

Reports may give SO4 or SO4-S. S = SO4 × 0.334.

## Don't confuse with

- **Sulfite (SO3 2-)**: a preservative and reduced form, not a fertiliser.
- **Sulfur**: the element; [elemental sulfur](https://genetixbay.com/knowledge/glossary/sulfur-burner.md) powder must be oxidised by microbes before plants can use it.

## Related terms

[Sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md), [Magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md), [Potassium sulfate](https://genetixbay.com/knowledge/glossary/potassium-sulfate.md), [Calcium](https://genetixbay.com/knowledge/glossary/calcium.md), [A/B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md)

## Read more

- [Sulfur (S) in cannabis: role, deficiency, targets and sulfate sources](https://genetixbay.com/knowledge/nutrients/sulfur.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
2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9