Flourish Iron™ is a highly concentrated (10,000 mg/L) ferrous iron gluconate supplement. Plants are able to much more easily derive a beneﬁt from Flourish Iron™ because ferrous iron gluconate is already in the ferrous form so they do not expend energy reducing it. Despite what other manufacturers may intimate, gluconate is not harmful to plants or fish.
Iron is immobile in plants. This means that plants cannot divert iron from older leaves to new ones. Therefore, deficiency symptoms appear first on new or young leaves. Because plants use iron to produce chlorophyll, a lack of iron results in chlorosis, or yellowing, of the younger leaves. Stems may also appear short and slender. If the deficiency is severe and prolonged, each new leaf emerges lighter in color than the preceding leaf.