Within days the leaves will turn dark green. Avoid iron deficiency by checking soil conditions before planting. If the soil is too acidic, correct the problem with sulfur. The amount to use depends on the change in acidity needed and the soil type. Maintain soil acidity by using natural fertilizers such as soybean meal or chemical fertilizers whose nitrogen is in the form of ammonium.
Organic matter can help prevent iron deficiency.
Mix some decomposed organic matter, such as peat moss or leaf mold, into the planting hole for a rhododendron, azalea, or other acid-loving shrub. Organic materials acidify the soil, loosen it to prevent waterlogging, and are sources of naturally occurring chelates.