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Gardening in Gwinnett: What to do about azaleas with yellow leaves

Many homeowners become concerned this time of year because the leaves on their azaleas are turning yellow. Often, the older leaves undergo this transformation while the younger ones stay green. However, sometimes many of them turn shades of yellow and orange.

It's normal for older leaves to turn yellow and die, as they are soon replaced by younger green leaves. But If most of the leaves are yellow, there's a problem.

The yellowing leaves may have been brought on by this year's drought. Azaleas are temperamental plants with a shallow, fibrous root system. They like moist, well-drained soils. Also, azaleas that have been planted in areas not suited for them, like in full sunlight, will also develop yellow leaves.

Another common culprit is lack of fertilizer. Yellowing azaleas likely did not receive adequate fertilization, especially nitrogen, during the growing season, or did not efficiently absorb the fertilizer that was applied due to stress.

The yellow leaves are no cause for worry. In most cases, they will bloom in the spring as they normally do. Do not fertilize them this time of year because fertilizer may cause the plants to break out of dormancy and start growing. The new growth is susceptible to frost and may be burned back by winter weather. Wait until after the danger of frost is past, roughly April 15 for our area. Plan on fertilizing them in early spring when they begin to leaf out. Use a general purpose fertilizer such as a 16-4-8 or 15-0-15.

Sometimes azaleas will have younger yellow or white leaves with green veins. This problem is caused by an iron deficiency, brought on by soils that aren't acidic enough. Azaleas prefer a lower pH (5.0 - 5.5) than many other plants (5.5 - 6.0) since iron is not as available to the plant at a higher pH. You can have your soil tested by the Cooperative Extension for a small fee. The test will tell you the pH. Azaleas have a higher iron requirement, and iron is more available in acidic soils. Applying a fertilizer iron spray or granules applied to the soil during at the labeled rate next spring should remedy the problem.

If you are planning on buying azaleas, or any other tree or shrub, to plant in you yard, now is a good time to do so. The top parts of the plants grow very little, but the roots will continue to grow and become established during the cold weather months. The plants are better able to handle the hot, dry conditions of the following spring or summer. Plant them in well-drained soils no deeper than the root ball. They prefer shade, but if they must be planted in a location that receives sun, morning sun will be the best.

If the azaleas receive the proper amount of sunlight, water, and nutrients, they are less likely to develop problems and are also less susceptible to pest attacks.

Timothy Daly, MS, is and Agricultural and Natural resource Extension Agent with Gwinnett County Extension. He can be contacted at 678-377-4010 or timothy.daly@gwinnettcounty.com.