# Manganese

> Manganese (Mn) is a micronutrient that splits water in photosynthesis and activates many enzymes; low pH can raise it to toxic levels.

- Canonical: https://genetixbay.com/knowledge/glossary/manganese.html
- Also written: Mn, Mn2+, manganese deficiency, manganese 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"

Manganese is a [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) absorbed as Mn2+. It is essential to the water-splitting complex of photosystem II and activates a range of enzymes. It is largely immobile in the plant. Its availability rises sharply as root-zone [pH](https://genetixbay.com/knowledge/glossary/ph.md) falls.

## In practice

[Deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) shows as interveinal mottling on young and middle leaves, with less contrast than iron [chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md) and sometimes small dead spots. It is most common at high pH. Toxicity is the more frequent problem in acidic soil or hydro run too low: brown speckling on older leaves and induced [iron deficiency](https://genetixbay.com/knowledge/glossary/iron.md), because Mn competes with Fe. Hydro feeds usually carry roughly 0.5-1 mg/L (ppm) Mn, typically from [manganese sulfate](https://genetixbay.com/knowledge/glossary/manganese-sulfate.md) or a chelate.

## Don't confuse with

- **Iron deficiency**: brighter yellow with sharper green veins on the newest leaves.
- **Magnesium deficiency**: older leaves, broad [interveinal yellowing](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md).
- **Rust-coloured spots from light or pathogens**: check pH and history before blaming Mn.

## Myth check

When Mn toxicity appears, the fix is usually raising root-zone pH back into range, not cutting the micronutrient blend. See [pH and nutrient availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md).

## Related terms

[Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Immobile nutrient](https://genetixbay.com/knowledge/glossary/immobile-nutrient.md), [Manganese sulfate](https://genetixbay.com/knowledge/glossary/manganese-sulfate.md), [Iron](https://genetixbay.com/knowledge/glossary/iron.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md)

## Read more

- [Manganese (Mn) in cannabis: netted chlorosis, low-pH toxicity and the iron balance](https://genetixbay.com/knowledge/nutrients/manganese.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