EDDHA, ethylenediamine-N,N'-bis(2-hydroxyphenylacetic acid), is a synthetic chelating agent used almost entirely for iron. Fe-EDDHA 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 in alkaline soils and with high-pH, hard water, where EDTA and DTPA 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 5.5-6.5 range, it is rarely necessary; DTPA usually covers drift. Using it as a short-term rescue for iron deficiency 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.
A chelate is a metal ion held by an organic molecule at several points, keeping micronutrients such as iron, zinc and manganese dissolved and available across a wider pH range.An iron chelate is iron bound to an organic molecule (EDTA, DTPA or EDDHA) that keeps it dissolved and available; each type holds up to a different pH.Yellowing of normally green plant tissue caused by too little chlorophyll, from nutrient shortage, poor root uptake, pH lockout, light damage, pests or normal ageing.General hardness (GH) is the calcium and magnesium dissolved in water, expressed as mg/L CaCO3 or German degrees (dGH); hard water supplies some Ca and Mg.EDTA (ethylenediaminetetraacetic acid) is the most common synthetic chelating agent in fertilisers, effective for iron up to about pH 6.0-6.5.DTPA (diethylenetriaminepentaacetic acid) is a synthetic chelating agent that keeps iron available up to about pH 7.0-7.5, a common choice for coco and hydro.pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.Iron (Fe) is an immobile micronutrient needed to make chlorophyll and run electron transport; deficiency yellows new leaves between green veins.
