# Potassium

> Potassium (K) is a mobile macronutrient that controls water balance, stomata and enzyme activity; deficiency scorches the edges of older leaves.

- Canonical: https://genetixbay.com/knowledge/glossary/potassium.html
- Also written: K, K+, kalium, potassium deficiency, K deficiency
- 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"

Potassium is a [macronutrient](https://genetixbay.com/knowledge/glossary/macronutrient.md) taken up as the K+ ion. It is not built into structures; it stays dissolved in the cell sap, where it regulates osmotic pressure, opens and closes stomata, activates dozens of enzymes and moves sugars through the phloem. It is highly mobile.

## In practice

[Deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) starts on older and middle leaves as yellowing and then brown, crispy margins and tips, sometimes with rust-like spotting. Hydro feeds commonly carry about 150-300 mg/L (ppm) K. Saloner and colleagues found cannabis needs less K than many bottle labels suggest, and that very high K mostly crowds out calcium and magnesium uptake rather than adding yield.

## Units and formula

Labels state potassium as K2O. Elemental K = K2O × 0.830. [Potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md) (13-0-46) is about 38% K; [monopotassium phosphate](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md) is about 28.7% K.

## Don't confuse with

- **Nutrient burn**: [tip burn](https://genetixbay.com/knowledge/glossary/nutrient-burn.md) from overall high [EC](https://genetixbay.com/knowledge/glossary/ec.md), not specifically low K.
- **Magnesium deficiency**: [interveinal yellowing](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md) on older leaves; K deficiency hits the leaf edges first.
- **Potash**: a trade word for potassium salts, not a separate nutrient.

## Related terms

[Macronutrient](https://genetixbay.com/knowledge/glossary/macronutrient.md), [Potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md), [Potassium sulfate](https://genetixbay.com/knowledge/glossary/potassium-sulfate.md), [Nutrient antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md), [Guaranteed analysis](https://genetixbay.com/knowledge/glossary/guaranteed-analysis.md)

## Read more

- [Potassium (K) in cannabis: role, deficiency, excess and K-Ca-Mg balance](https://genetixbay.com/knowledge/nutrients/potassium.md)

## Sources

1. Saloner A, Sacks MM, Bernstein N. 2019. Response of medical cannabis (Cannabis sativa L.) genotypes to K supply under long photoperiod. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369
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