Azaleas are flowering evergreen shrubs that are part of the Rhododendron genus. Azaleas compose two of eight different Rhododendron subgenera--evergreen (Tsutsuji) and deciduous (Pentanthera). They are either hybrids or species. Azaleas have been hybridized for centuries.
Azaleas thrive in soil that is well-drained. For azaleas that are grown indoors, it is optimal for them to be in shady and cool spots. Too much moisture of the soil can damage azaleas. Slightly acidic soil is preferable for the plants (a pH range of between 4.5 and 6). Fertilizer can be used, but is optional. For some types of azaleas, pruning might be necessary.
One common disease that can affect azaleas is called azalea leafy gall. This can destroy the leaves of the plant toward the beginning of the spring. The best way to control, manage and eliminate azalea leafy gall is by picking the leaves that are infected by hand. The disease is characterized by fleshy galls (resulting from a fungus called Exobasidium vaccinii) appearing on the branch tips, leaves, seedpods and flower parts. The galls can be pink, light green, brown or white. Other possible diseases are twig blight, rust (a fungal disease), powdery mildew and petal blight.
Deciduous and Evergreen
All of the species of azaleas in North America are deciduous. These azaleas are also known as native azaleas and can come in various colors, including purple, white, yellow, orange, red and pink. Evergreen azaleas generally originate in Japan, and can be pink, purple, white, red and reddish-orange. They are never yellow.
In general, azaleas are hardy and pest-free plants. However, there are occasional pests that can damage azaleas. These pests include caterpillars, bark scale, leafminers, lace bugs, whiteflies and stunt nematodes. Some methods of control and eliminating are handpicking, insecticidal soap, branch removal and proper watering and fertility practices.
Environmental factors can also bring upon problems for azaleas. Nutritional deficiencies (especially iron and nitrogen) can cause discoloration of the foliage, as well as undersized flowers and leaves. Improper watering practices can also be problematic, and can result in the foliage being discolored, wilting and dropping. Excessive or insufficient amounts of light can also damage azaleas. One such example is leaf scorch, which is caused by excessive sun and is characterized by brown or yellow spots appearing on the foliage.