Flourish Iron is a highly concentrated (10,000 mg/L) ferrous iron (Fe+2) gluconate supplement. It should be used in those cases where the iron requirements exceed that which can be delivered by Flourish at the recommended dose or signs of iron deficiency appear (such as short and slender stems or yellowing between veins.) Contains no phosphate or nitrate. Plants are able to much more easily derive a benefit from Flourish Iron than from EDTA-iron sources because all EDTA iron is in the ferric (Fe+3) state. Since plants require iron in the ferrous (Fe+2) state, additional physiological energy must be expended in order to extract the ferric iron from EDTA-iron and then convert it to the ferrous form.