- 1). Troubleshoot the cause of your azalea's yellow foliage. The shrub's shallow roots are prone to injury both in periods of drought and flooding, which results in yellowing leaves. Prune the affected leaves. If the weather is the problem, wait to see whether the shrub recovers from the stress. Do not fertilize it. Next time you plant an azalea, set it in a raised bed to keep the soil drained when the area floods. Prevent drought stress by supplementing 1 inch of water weekly during periods of no rain. Keep the roots moist with a 3-inch layer of mulch, such as wood chips or bark, around the shrub's base.
- 2). Get a soil test done to check pH and nitrogen levels. Azaleas require a soil pH between 4.5 and 6.0. They also need nitrogen to thrive. The roots can't tap into the ground's nutrient supply if the pH is wrong. Likewise, if the pH is ideal, but the soil is depleted, azaleas show signs of malnourishment, yellow leaves included. Acidifying the soil is difficult and it has a temporary effect. If the soil pH is the problem, grow azaleas in pots filled with mixes formulated for them. If the ground lacks nitrogen, follow the recommendations given in the lab report for improving it. Azaleas need 1 pound of nitrogen per 1,000 square feet, in general. Broadcast the feed in a circle that extends 2 feet beyond the shrub's drip line. Water it in. Don't let the fertilizer touch the plant.
- 3). Treat your azalea shrub for iron deficiency if its newly sprouted leaves come out yellow. Select an iron supplement labeled for soil application. The rate of fertilizer per square foot varies according to the brand. Follow the instructions on the label of the product you selected.
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