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What to do when leaves turn yellow with chlorosis.

What to do when leaves turn yellow with chlorosis

It's not always easy to cure iron chlorosis --a common ailment of many garden plants that causes leaf tissue between the veins to turn yellow. Iron may be lacking in the soil, but more often--especially in alkaline soils--it is present but unavailable to plant roots because it is insoluble. Cold, wet, or poorly drained soil aggravates a chlorotic condition.

There are several methods available to treat iron chlorosis. Some are only temporary, others are long-lasting.

Sprinkling and spraying. Chelated iron sprinkled within the drip line will usually green up the leaves in two to three weeks (apply it to bare soil, since a lawn will tie most of it up). On a tree, this treatment may last a couple of years.

Or, if the tree is not too large and you have an adequate spraying system, spray chelated iron directly onto the foliage (this will last only about one season). In both cases, follow package directions.

Improving the soil. The longest-lasting solution is to correct watering practices (if necessary) or to acidify the soil with sulfur. First, check soil moisture by digging down which a trowel. If the soil is too wet, reduce watering and wait to see if the plant greens up in late spring.

If you can't reduce watering because the plant is growing in a lawn, or if it doesn't green up as the soil dries out, you probably need to acidify the soil. You also need to do this if the soil is simply too alkaline. To find out, have its pH tested at a soil-testing lab (look in the yellow pages under Laboratories--Testing).

Depending on how alkaline the soil is and whether the soil is sandy or clayey, adjust the pH by applying 2 to 4 pounds of soil sulfur per 100 square feet to the soil within the plant's drip line (use lower amounts in sandy soil). Work the sulfur into the top of the soil. Most types of soil sulfur act slowly (months may pass before you see improvement), so use chelated iron as well to green up the foliage quickly.

If the plant is growing in a lawn, get soil sulfur down to the roots by applying it in holes under the drip line (to learn how, see "Tips for beginning gardeners' on page 176 of the March 1987 Sunset).

You can use iron sulfate to green up the foliage--it will usually last at least five years--but it acts slowly and it won't change the soil pH.

When plants need nitrogen, apply ammonium sulfate, which tends to lower the soil pH.

Quick-fix implants. Another treatment available in nurseries for trees and large shrubs is the fertilizer implant--an inch-long capsule containing iron and sometimes other micronutrients. You embed 3 to 10 or more of them into the trunk (depending on its diameter) in 1 1/4-inch-deep holes you drill every 3 to 4 inches in a spiral pattern. They cause the leaves to green up quickly.

But the cure is temporary and potentially damaging; it should be used only as a last resort.

If soil conditions remain unchanged, the leaves will turn chlorotic again in a year or two, and then you must repeat the treatment.

Also, this quick-fix approach can disfigure the trunk and may weaken the tree, especially if it must be repeated. Any puncturing of the bark opens the tree to possible invasion by disease and decay organisms. Recent research shows that the fertilizer in the capsule can also damage the wood surrounding the hole. And if the trunk gets wet or sap leaks out where the capsules are implanted, the ooze may discolor the bark.

Photo: First sign of iron chlorosis on these grapefruit leaves is yellowing between green veins. In advanced cases, entire leaves may yellow
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Copyright 1988 Gale, Cengage Learning. All rights reserved.

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Date:Feb 1, 1988
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