It is generally believed that if the foliage of plants is visibly green, iron‐deficiency problems do not exist. There are at least five conditions under which plants may respond to iron even when green: (1) If the soil solution or irrigation water contain more than 1 or 2 me/L bicarbonate, (2) If leaf concentrations of iron are below between 40 to 70 mg/kg dry weight, (3) In the new leaf growth of most trees and vines, (4) During the first one of more days in the life of a seedling, and (5) When crops are pushed to very high yields. SPAD leaf color readings or chlorophyll analyses may detect some of the possibilities. The Sufficiency Values for iron have to be less than the maximum of 1.00 in order for these iron responses to occur. Considerable programs in plant breeding and genetics are being conducted to improve the efficiency of plants for iron nutrition, but these efforts will mostly insure that iron is not a severe Liebig type limiting factor. Many or most of the physiology which relates to the five factors above, even with iron‐efficient cultivars, will continue to result in slight Mitscherlich type limiting factors that involve iron. Avoidance of environmental mismanagement will continue to be a major factor in preventing iron deficiency. Sustainable practices help avoid iron deficiency.