# Iron

> Iron (Fe) is an immobile micronutrient needed to make chlorophyll and run electron transport; deficiency yellows new leaves between green veins.

- Canonical: https://genetixbay.com/knowledge/glossary/iron.html
- Also written: Fe, Fe2+, Fe3+, iron deficiency, Fe 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"

Iron is a micronutrient required for chlorophyll synthesis and for the cytochromes and iron-sulfur proteins that carry electrons in photosynthesis and respiration. It is immobile, so the plant cannot move it from old leaves to new ones. In solution, iron precipitates as insoluble hydroxides as [pH](https://genetixbay.com/knowledge/glossary/ph.md) rises, so feeds supply it as a [chelate](https://genetixbay.com/knowledge/glossary/chelate.md).

## In practice

[Deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) appears as [interveinal chlorosis](https://genetixbay.com/knowledge/glossary/interveinal-chlorosis.md) on the newest leaves: bright yellow tissue with fine green veins, in severe cases nearly white. The usual cause is high root-zone pH, not a lack of iron in the bottle. Hydro feeds typically carry about 1-3 mg/L (ppm) Fe. Which chelate is used matters: EDTA-iron loses effectiveness above about pH 6.5, DTPA holds to about 7.5, and EDDHA well beyond.

## Don't confuse with

- **Magnesium deficiency**: interveinal too, but on older leaves.
- **Manganese deficiency**: interveinal mottling with less contrast, often on middle leaves.
- **Nitrogen deficiency**: uniform yellowing of old leaves.

## Myth check

Adding more iron rarely fixes iron [chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md) when pH is the problem. Correct the root-zone pH first. 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), [Iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md), [EDTA](https://genetixbay.com/knowledge/glossary/edta.md), [DTPA](https://genetixbay.com/knowledge/glossary/dtpa.md), [EDDHA](https://genetixbay.com/knowledge/glossary/eddha.md)

## Read more

- [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md)
- [Yellow new growth on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellow-new-growth.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. HortScience. 2025. Iron chelates (Fe-EDTA, Fe-DTPA, Fe-EDDHA) in high-pH soilless media. HortScience 60(3):404. https://journals.ashs.org/view/journals/hortsci/60/3/article-p404.xml