Iron is immobile in plants; this means that plants cannot deliver 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.

propel is a concentrated (10,000 mg/L) source of ferrous iron. This ferrous iron is a mixture of readily available and time-released iron.

If iron is provided in the ferric form (Fe3+) then it must be reduced by the plant to the ferrous form (Fe2+) before it can be utilized. This process of conversion (known as reduction) requires the plant to expend physiological energy. propel provides iron already in the ferrous form thus enhancing iron utilization. In addition, propel contains a reducing agent that helps convert any iron present (such as iron from substrate) into the ferrous form.