Azaleas are one of the most popular landscaping shrubs in gardens today. Their open sprawling growth habit and vast array of colorful flowers make them useful in many landscaping situations. Some are even evergreen, giving a winter interest to the landscape. However azaleas prefer an acidic soil, which means a little extra maintenance for the gardener. Soil tests and special fertilizers are a must for the health of the plant. In most cases, home gardeners don't mind the extra work in exchange for the beautiful flowers throughout the growing season.
Obtain a soil test from your local extension center to determine the pH, or acidity, of the soil. Azaleas thrive in soil with a pH between 4.5 and 6.
Apply a wettable sulfur or ferrous sulfate to the soil in the amount needed to lower the pH according to the results of the soil test. Do not use aluminum sulfate as it is toxic to azalea roots.
Spread a 2-inch layer of compost on the soil over the root area. As you water, the compost will leach into the soil and supply nutrients to the plant.
Place a 4-inch layer of shredded bark or pine straw under the spread of the shrub. Keep the mulch 3 inches away from the trunk. As the mulch decays it will act as a type of fertilizer for the shrub.
Apply an azalea-specific fertilizer over the mulch just after flowering. Apply to the shrub while it is dry. Try to broadcast the fertilizer so it does not land on the foliage; but if it does, brush it off with a dust pan brush or broom. Water the azalea immediately after application to rinse it off the foliage and leach it into the soil. Follow the manufacturer's directions on how much to use.
Use another weaker application again in June to spring-flowering shrubs. Azaleas planted in sandy soils may need more frequent, weaker applications due to the extra water washing the fertilizer out of the soil. Follow the manufacturer's suggestions on fertilizing for soil types.