Chelated iron is iron (Fe) that has been chemically bonded to an organic molecule (a chelate) to keep it soluble and plant-available in nutrient solutions. Unchelated iron rapidly oxidises and precipitates out of solution at normal growing pH levels, becoming inaccessible to plant roots. The most common chelating agents are EDTA (stable up to pH 6.0), DTPA (stable up to pH 6.5), and EDDHA (stable up to pH 9.0).
Key Facts
- Unchelated iron precipitates above pH 6.5 and becomes unavailable to plants
- EDTA chelate: effective at pH 4.0β6.0 β suitable for most hydroponic systems
- DTPA chelate: effective up to pH 6.5 β better for slightly higher pH ranges
- EDDHA chelate: stable up to pH 9.0 β used in soil and high-alkalinity water
- Iron deficiency causes interveinal chlorosis on new leaves (yellowing between green veins)
- Most complete hydroponic nutrients contain EDTA or DTPA chelated iron