Iron Chlorosis*

Iron Chlorosis*

By Dr. Gene Holm, Mini-Cassia Master Gardener

Iron is necessary for the formation of chlorophyll, which is responsible for the green color in plants and is the source of plant food and energy. When the amount of iron available to plants is inadequate for normal growth, leaves become pale yellow, yellow or white and eventually brown, particularly between the veins. Mildly affected plants become unsightly and grow poorly. Severely affected plants fail to grow flower or fruit and may even die from lack of iron.

Iron chlorosis may occur as a result on one or a combination of causes. The condition is often due to high pH, which makes it possible for other elements to interfere with the absorption of iron, rather than a lack of iron in the soil. This occurs in neutral to alkaline soils when the pH is above 6.5.

Chlorosis may be cause by an actual deficiency of iron or by application of excessive amounts of lime or phosphate to certain soils. It may be caused by over-watering, poor drainage or high levels of certain mineral elements in the soil such as manganese, copper or zinc.

The pH, particularly in southern Idaho, is quite often above 7. For permanent control, this must be lowered by annually applying to the soil ammonium sulfate, aluminum sulfate or sulfur.

Once other possible causes have been corrected, application of iron may not be needed. If, however, plants remain chlorotic, iron can be supplied to plants in different forms.

The two principal types of iron-containing materials are iron chelates, organic in nature, and inorganic compounds in soluble form such as ferrous sulfate. Iron chelates are marketed under various trade names and in various formulations. The iron in chelates remains available to plants when the chelates are placed in the soil. Some formulation of iron chelate can be applied to the foliage; however, this approach is usually not as permanent as soil applications. Follow the manufacturer’s recommendations for amount of use. Some fertilizers contain iron chelates, and use of these with plants susceptible to iron deficiency is recommended. Ferrous sulfate can also be applied to the soil or foliage.

When leaves of plants become chlorotic, always determine the primary cause then take the necessary steps to prevent further damage.

For a severe case of chlorosis, use one of the following products: Acid Iron, for trees and shrubs, from Landview Chemical, located in Minidoka. Their fieldmen will deliver. It has manganese in it and should not be used in consecutive years. Sulfegro from Simplots between Rupert and Heyburn.

These products are expensive but turnaround is 7 to 10 days. If you use chelated iron, while cheaper, you may need multiple treatments and may take 3-4 weeks before seeing a noticeable difference.

*ref. Ohio Stat University Extension Fact Sheet