# Molybdenum

> Molybdenum (Mo) is the micronutrient needed in the smallest amount; plants need it to convert nitrate into usable nitrogen.

- Canonical: https://genetixbay.com/knowledge/glossary/molybdenum.html
- Also written: Mo, molybdate, MoO4 2-, molybdenum 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"

Molybdenum is a [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) absorbed as the molybdate anion (MoO4 2-). It is the metal centre of [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md) reductase, the enzyme that turns nitrate into nitrite on the way to amino acids. Without it, a nitrate-fed plant can starve for nitrogen while nitrate builds up in its tissue. Unlike most micronutrients, molybdenum becomes more available as [pH](https://genetixbay.com/knowledge/glossary/ph.md) rises.

## In practice

[Deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) is uncommon. It shows as pale, yellowing middle and older leaves with cupped or scorched margins, resembling [nitrogen deficiency](https://genetixbay.com/knowledge/glossary/nitrogen.md). Low pH makes it more likely. Hydro feeds carry tiny amounts, often around 0.03-0.05 mg/L (ppm) Mo, usually from [sodium molybdate](https://genetixbay.com/knowledge/glossary/sodium-molybdate.md) or [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) molybdate.

## Don't confuse with

- **Nitrogen deficiency**: very similar look; Mo deficiency can occur with plenty of nitrate in the feed.
- **Manganese**: different element; the symbols Mn and Mo are easy to mix up.
- **Magnesium (Mg)**: also easy to confuse by symbol.

## Related terms

[Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Sodium molybdate](https://genetixbay.com/knowledge/glossary/sodium-molybdate.md), [Nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md), [Mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md)

## Read more

- [Molybdenum (Mo) in cannabis: the trace element nitrate depends on](https://genetixbay.com/knowledge/nutrients/molybdenum.md)

## Sources

1. Kaiser BN, Gridley KL, Brady JN, Phillips T, Tyerman SD. 2005. The role of molybdenum in agricultural plant production. Annals of Botany 96(5):745-754. https://doi.org/10.1093/aob/mci226
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