All green plants depend upon chlorophyll for photosynthesis. Iron is a key nutrient in the production of chlorophyll and a critical element in plant respiration. Without this essential element, iron deficient foliage becomes chlorotic--leaves begin to appear yellow between still green veins and the plant is unable to generate adequate energy to manufacture food for survival. When analysis indicates that an iron deficiency exists, it is crucial that iron--in appropriate form--be made available to stricken plants.
Apply chelated iron to obviously deficient plants (following manufacturers application directions) as a foliar spray or directly to soil near the plant's drip line. Chelated iron is a particularly soluble form of iron that is almost immediately absorbed by plant tissue, so treated plants should rapidly show signs of improvement. This will improve severe cases but is a temporary fix.
Assess soil conditions to determine more lasting solutions to the problem. Over-watered, stagnant or poorly compacted soil can inhibit root aeration. Plants will be unable to properly take in iron if the physical environment is unhealthy, therefore, improvement of drainage problems is a critical first step toward a permanent fix.
Determine the pH level of the soil around affected plants--pH above 6.5 may indicate soil is too alkaline. As far as plants are concerned, iron only exists in usable form when soil pH is around 5.0 to 6.5. Under higher pH conditions, iron may be present in sufficient amounts, but unavailable to growing plants, therefore, increasing soil acidity is essential.
Correct soil pH levels that allowed the iron deficiency to occur. The addition of elemental sulphur (following manufacturers application directions) to overly alkaline soil will help restore pH values to levels necessary for iron and other minerals to be available to growing vegetation on a more permanent basis. For minor pH adjustments, application of peat moss or other soil acidifiers may be enough.
Add bone meal, blood meal or iron sulfate if soil tests indicate your soil is still low in iron, but soil pH is corrected.