Instructions for each product should be followed closely. Crops considered tolerant of low levels of iron include alfalfa, barley, grasses, oats, wheat -to list a few. With the exception of ferrous sulfate, perhaps the most widely used iron sources are the synthetic chelates and natural organic complexes. These materials are water soluble and can be applied to the soil or foliage. Iron in chelated forms and in organic complexes are protected from the usual soil reactions.
Ferrous sulfate can turn grass black-green for a couple of weeks, but does no permanent damage.
Also, it may cause rust spots on the sidewalk and other concrete. Usually with pH in that range, we do not often get the iron deficiency. However, some crops show it readily at anything above about 6.0, so it really depends on the crop.