Question: Our azaleas on the eastern side of the house have never been very showy. The flowers are always puny and short-lived. This year one plant’s leaves are quite yellow. Is this is sign of disease or need for fertilizer? Any advice on helping the plants do better?
First, consider what azaleas need to grow well, and you may find that one or more of these conditions (outlined by the Azalea Society of America) is not being met:
-Slightly acid soil (pH 5.5 – 6; a soil test can provide that information about the soil in your azalea bed).
-Enough sunlight. Less than 3 hours of sun reduces the number of buds.
-Adequate moisture. Like many other shrubs and perennials in the garden, azaleas need about an inch of water (rainfall or watering) per week. Mulch around the shrubs can help the soil retain moisture.
There are several factors that affect the number of blooms — including the fact that some are just “shy bloomers,” according to the Azalea Society. Lack of moisture during late spring and summer also affect bud formation, or there may be a phosphorous deficiency (again, the soil test can determine if that’s the case).
As for those yellow leaves: If the yellowing is between dark green veins, the condition is called chlorosis, which is usually caused by an iron deficiency, alkalinity of the soil, potassium, calcium or magnesium deficiency, or too much phosphorous. Iron sulfate or sulfur can acidify the soil.
Leaves that are uniformly a yellow – green color may just need more nitrogen. That soil test should be your first step to determine what the problem may be.