Azaleas are in the genus Rhododendron, with evergreen azaleas in the subgenus Tsutsusi and deciduous azaleas in the subgenus Pentanthera.
Some small-leaved rhododendrons look like evergreen azaleas. To tell them apart, first look at a flower—most azaleas have only 5 or 6 stamens, while most rhododendrons have 10 stamens.
Azaleas are relatively pest-free, forgiving and easy to grow plants. Their cultural needs include:
Moderate temperatures (USDA cold hardiness zones 6 to 8, minimum -10 to +20° F.), although many varieties can thrive in much lower temperatures, and others in much higher temperatures.
High shade is preferable but some varieties do well in full sun, especially deciduous varieties. While more sun typically produces more compact plants with more blooms, the blooms will not last as long.
Slightly acid soil (pH 5.5-6) is best and is usually found under oak, pine and holly trees.
A mulch of pine bark, pine needles or wood chips helps to keep moisture in the ground, even out changes in the soil temperature, and keep weeds out. An inch or so around the root zone and a thicker layer between the plants is desirable.
Azaleas do not like "wet feet". Good drainage is most easily provided by planting azaleas with the tops of their root balls a few inches above ground level and mounding the soil up to the plants. This is particularly important with heavy clay soil.
Azaleas like moist soil at their roots. This may require supplemental watering through early fall, at least until plants are established in the ground for a few years. Adequate water after bloom helps to produce more flower buds for next year. An infrequent deep soaking is more effective than superficial sprinkling. The amount of water needed depends on the soil, temperature, humidity, wind and sunlight. In a dry fall, water heavily after a good frost, before cold weather sets in.
Established azaleas do not need fertilizer. To avoid inducing new growth which may be killed in the winter, do any fertilizing in late winter or early spring; never after July 1.
To avoid cutting off next year's flower buds, do major pruning of azaleas soon after they bloom. Shortening or removal of long slender stems with no side shoots and cutting out dead wood may be done at any time.
As needed, a fungicidal spray in the spring as the buds show color will control petal blight, a fungal disease that appears as discolored dots on the petals and quickly discolors and collapses the blossoms.