Buy in bloom. Most people have a particular color in mind when they buy azaleas. One way to guarantee the color you want is to buy flowering plants. You will be sure to get the right color, and if you are buying several you can see if they match or blend.
Speaking of color. To get the most impact, set out blocks or sweeps of the same selection. Ten types scattered across the front of your house will be colorful but chaotic.
Consider size. Not all azaleas are low-growing shrubs. The Southern Indian hybrids reach 8 to 10 feet tall in some parts of the South and should be planted at least 4 feet apart. Some zealous gardeners don't realize this and soon find their sidewalks and houses consumed.
The medium-size Kurumes grow 3 to 5 feet tall and need a 30-inch spacing. Satsuki hybrids--including Gumpo, Macrantha, and Wakaebisu--generally grow less than 3 feet tall and are perfect for planting under low windows. Satsukis can be placed 2 feet apart for a nice full look. Don't crowd new plants together; space them for the future, not for instant effect.
A little shade, please. When choosing the best spot to plant, take the sun into account. Azaleas like plenty of morning light. However, avoid areas that get midday or hot afternoon sun--plants in full sun are susceptible to lacebugs and spider mites.
Azaleas need acid soil. Adding plenty of leaf mold, peat moss, or bark can help create the ideal environment. This is particularly important if you're placing the plants near your home's foundation, where lime can leach out of the concrete and neutralize acid soils. Limestone gravel used for drainage around your home can also cause soil to be too alkaline.
In alkaline soils (like those in Texas and Arkansas), you may want to try growing a few specimens in containers.
Moisture. Avoid planting azaleas near downspouts or areas that stay damp. In heavy clay soil, plant them almost on top of the ground, building soil up on the sides of the root ball.
Planting in clay. Dig a hole as deep as the root ball and twice as wide. Add soil enriched with organic matter to the hole so that the top of the root ball will sit 4 inches above ground level. Place the root ball in the hole, and build up the soil on the sides. Planting high gives the shrub the drainage it needs, but you will need to water frequently.
About pruning. Avoid the urge to shear your plants into round balls or other geometric forms. Azaleas look best when allowed to grow to their natural mounded shape. Limit pruning to removing long, stray branches. Older plants that have become leggy may benefit from pruning branches from the main trunk in staggered lengths. If you have to prune hard every year, you probably have the wrong azalea for that location, or your plants are too close together.
Azalea concerns. Don't worry when a few leaves turn yellow and drop off, especially in the fall. All evergreens drop some leaves during the year. If autumn is mild, azaleas will often bloom. There is nothing you can do to prevent this. Enjoy the fall blooms, because flowering could be sparse the following spring.
"Azalea Plant Chart" is from the Southern Living Spring Garden Guide, 2000.