# EDDHA

> EDDHA is a strong iron chelate that stays effective up to pH 9 or more, used for alkaline soils and hard water; it colours solutions dark red.

- Canonical: https://genetixbay.com/knowledge/glossary/eddha.html
- Also written: EDDHA chelate, ethylenediamine di(o-hydroxyphenylacetic) acid, EDDHA iron, red iron chelate
- 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"

EDDHA, ethylenediamine-N,N'-bis(2-hydroxyphenylacetic acid), is a synthetic [chelating agent](https://genetixbay.com/knowledge/glossary/chelate.md) used almost entirely for iron. [Fe-EDDHA](https://genetixbay.com/knowledge/glossary/iron-chelate.md) products typically contain about 6% Fe. The quality of EDDHA products depends on the share of iron held in the more stable ortho-ortho form, which labels may state.

## In practice

Fe-EDDHA is the fix for iron [chlorosis](https://genetixbay.com/knowledge/glossary/chlorosis.md) in alkaline soils and with high-pH, [hard water](https://genetixbay.com/knowledge/glossary/general-hardness.md), where [EDTA](https://genetixbay.com/knowledge/glossary/edta.md) and [DTPA](https://genetixbay.com/knowledge/glossary/dtpa.md) fail. It costs more per gram of iron. It stains water, reservoirs and runoff a deep wine-red, which alarms growers the first time. For hydro kept in the usual [pH](https://genetixbay.com/knowledge/glossary/ph.md) 5.5-6.5 range, it is rarely necessary; DTPA usually covers drift. Using it as a short-term rescue for [iron deficiency](https://genetixbay.com/knowledge/glossary/iron.md) in high-pH soil is a common practice.

## Don't confuse with

- **EDTA**: cheaper, works only below about pH 6.5.
- **DTPA**: middle ground, good to about pH 7.5.
- **Red runoff from organic matter**: tannins or humics, not EDDHA.

## Related terms

[Chelate](https://genetixbay.com/knowledge/glossary/chelate.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), [Iron](https://genetixbay.com/knowledge/glossary/iron.md)

## Read more

- [Iron (Fe) in cannabis: yellow new growth, chelates and pH](https://genetixbay.com/knowledge/nutrients/iron.md)
- [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md)

## Sources

1. 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
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