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The ongoing saga of plant maladies is not complete without understanding iron chlorosis. Iron chlorosis is the most common and most serious plant micronutrient deficiency and is the most difficult to correct.
I have never accumulated a comprehensive list of plants susceptible to iron chlorosis, but such a list would be extensive. Fruit trees, grapes, raspberries, strawberries, and other fruiting plants are all affected. Roses, junipers, bridal wreath, barberry and cotoneasters as well as catalpas, silver maples, oaks, liquid amber, and many other species show chlorosis. Even annual plants are not safe as iron chlorosis shows in vegetables and flower gardens regularly.
Iron chlorosis shows as yellow leaf with thin green veins. As conditions worsen, the leaf turns pale yellow and then to ivory white. Veins remain darker than the surrounding tissue, and with a severe problem the leaves turn brown and die. Deficiencies show on the entire plants, on one side of the plant or even on a single branch.
In Utah, iron chlorosis is an iron deficiency within the plant. It is not caused by lack of iron in the soil! Red rocks and rusty water stains are the result of an abundance of iron. Unfortunately, the high pH and lime content of our soil makes this iron unavailable to the plant. Gardeners can do little to change this problem, but they can correct other problems.
Excessive watering is a major cause of iron chlorosis. Excessive early season irrigation is a major problem. Fruit trees and grapes do not require frequent irrigation and do not require irrigating prior to blossoming. Stretch the irrigation intervals as long as possible. Poor drainage adds to the problem. Susceptible varieties in clay soils should be planted on raised beds to improve the drainage.
Another major culprit is overuse of high-phosphate fertilizers. Many gardeners add more than needed, just to make sure they are not short on fertilizer, but this aggravates iron chlorosis. Mechanical injury is also a serious problem. Root diseases, trunk girdling with lawnmowers or weed eaters, cutting roots during construction, or even insect damage interferes with the plant's ability to move iron into the root, up the trunk and out into the leaves.
Plants suffering from iron chlorosis do not grow well, do not produce good fruit and are less winter hardy. Controlling iron chlorosis is frustrating and expensive. Adding iron materials to the soil is often recommended but should be done only after other methods have been tried. One common method mentioned in many garden texts is lowering the soil pH. This is not possible in Utah because of high lime soils. The idea sounds enticing, but don't fall for unproven treatments.
Iron sulfate and iron containing fertilizers work well to correct iron deficiency in turfgrass but are almost useless on vegetables or woody plants. It is much like adding rusty nails or iron filings or other forms of unavailable iron to the soil. As mentioned, there is plenty of iron in the soil, and adding more of unavailable forms is not helpful.
Some iron-containing products work under our conditions. The most reliable products (which incidentally are also the most expensive) are Fe Sequestrene 138 or Millers Ferriplus Iron. These are both the same product, but the first is sold in five-pound packages and the second in one-pound packages.
Organic chelates including products such as Ruffin and Tough iron work well if the problem isn't too severe. Other products can be used as foliar sprays. These give little benefit when applied to the soil but give some control if applied as a foliar spray every 10 to 14 days. Follow label directions carefully as iron can burn leaves, stain fruit and stain concrete.
Two less expensive products work in some situations - Ironrite and Iron Sul. These are by-products of the smelting industry and have a very acid pH. They provide iron by a temporary lowering of the pH in areas where they are applied. Iron is needed in very small amounts, and these products may help.
The best way to avoid iron chlorosis is correct selection of plant materials. If you have heavy clay, high pH soils and questionable water quality, don't plant susceptible plants.
While you may long for Concord grapes, peach trees, azaleas and rhododendrons, you'll spend too much time and money and get only more frustrations. Try to control the problem by planting varieties less susceptible to iron chlorosis.
Improve soil drainage, control irrigation, avoid damage to the plant and avoid excessive phosphorus fertilizer to help control this problem. The ultimate test is whether the plant grows, survives and flourishes under your growing conditions. Careful attention will reward you with beautiful healthy plants, but neglect means yellow leaves and the decline and death of your plants.
