EDTA, ethylenediaminetetraacetic acid, is a synthetic chelating agent that binds metal ions at six points. In fertilisers it carries iron (Fe-EDTA, about 13% Fe), and often zinc, manganese and copper. It is cheap and widely used.
In practice
Fe-EDTA works well in hydro and soilless media kept around pH 5.5-6.2. Above about 6.5 its iron becomes progressively less available, so it is a weak choice for alkaline water, high-pH soil or coco run high. Fe-EDTA also breaks down under strong light, so clear reservoirs and lines exposed to light lose iron faster. At high pH, EDTA can also pick up calcium, displacing the iron it carries. EDTA is not readily biodegradable, which has raised environmental questions about its heavy use in agriculture.
Don't confuse with
- DTPA: a related chelate, stable to a higher pH.
- EDDHA: much more stable at high pH, used for alkaline soils.
- HEDTA: a related chelate with intermediate properties.
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.Manganese (Mn) is a micronutrient that splits water in photosynthesis and activates many enzymes; low pH can raise it to toxic levels.A soilless medium contains no mineral soil, such as peat, coco, rockwool or perlite blends, and relies mostly on the grower to supply nutrients.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.Coco coir is a growing medium made from processed coconut husk, prized for holding water and air at once; it binds calcium and magnesium unless buffered.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.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.Iron (Fe) is an immobile micronutrient needed to make chlorophyll and run electron transport; deficiency yellows new leaves between green veins.
