Azaleas are a true sign of spring and a staple plant for the southern landscape with many different varieties and types. The first Southern hybrid azaleas were planted in Charleston, S.C., in 1848. Today, azaleas can be found in every climatic region in the eastern half of the United States and also in most of the Pacific Coast region. In Alabama, we have deciduous and evergreen varieties of azaleas. The native deciduous azaleas lose their leaves in the winter, but have very beautiful clusters of honeysuckle-like flowers in early spring, adding great flower color and texture to the landscape. More commonly seen in the landscapes are the evergreen azaleas available in many different varieties of size and flower color.
If you are thinking of adding azaleas to your landscape both the native deciduous and evergreen types are great choices for areas with filtered shade. Very heavy shade throughout the day may reduce flower production and result in weak growth.
Azaleas do require some special treatment when it comes to soil conditions. They require an acid soil pH (around 5.5) to grow properly. Check the soil pH of your site before planting. The reason azaleas do better in slightly acid soil is because iron is more available to be taken up by the plants, which azaleas need. If the leaves of your azaleas have a yellow tint to them and the area between the veins is lighter in color than the darker green veins, the plants are not getting enough iron. Other causes of chlorosis (yellowing symptoms) in azaleas may also be attributed to poorly aerated soil, a heavy application of fertilizer or roots heavily infested with nematodes or infected with root-rot disease organisms.
A big problem in azalea culture is over-fertilizing, especially with phosphorus. Too much fertilizer injures the plants and may even cause them to die. Be particularly careful with small plants using no more than 1 teaspoon of fertilizer at a time on plants less than 12 inches tall. For larger plants, use 1 heaping tablespoon per foot of height, scattering the fertilizer under the plant. It is best to split the recommended amount into two applications making a light application after blooming and another in July than to apply the yearly recommendation all at once.
The best way to avoid over-fertilizing your azaleas is to have your soil tested every 2 or 3 years and follow the recommendations. If you don’t have a soil test, use an all-purpose fertilizer such as 8-8-8 or 12-6-6. Some special azalea-camellia formulations are available and cater to the acid soil requirements of these plants.
In Alabama, many azaleas begin to set flower buds in July. Therefore, pruning after early July may reduce the next year’s flower production. The best time to prune is right after the flowering period in the spring before the new buds are set. Cut out the limbs that have grown out of the main body of the plant. Do not shear unless your intention is to create a formal hedge.
Serious pests of azaleas are spider mites and lace bugs. Spider mites are serious pests of many ornamentals such as roses, boxwoods and azaleas. Adult spider mites vary in size and may be green, orange, red, brown, black or a combination of these, but red is the most common. Spider mites puncture the tissue of leaves and flowers with needle-like mouthparts and suck juices from the plant. This destroys the chlorophyll around the puncture, giving the leaves and flowers a speckled appearance. As mites multiply, entire leaves become discolored and distorted and may drop off. These pests are very small and feed mainly on the underside of leaves. They often go unnoticed until plant damage is obvious.
Azalea lace bugs are very small insects with black bodies and colored or variegated lace-like wings. They also feed on the underside of leaves. The upper leaf surface opposite the feeding areas becomes speckled and the leaf looks light or bleached and eventually turns brown. Lace bugs give off large amounts of a dark, almost black, sticky substance you will find on the underside of leaves. Black, raised bumps on the lower surface of the leaves are an obvious symptom of this insect.
Chemical control gives best results when used in the spring to control the spider mites and the first and second generations of azalea lace bugs. Products such as insecticidal soap, horticultural oil, neem oil and most synthetic insecticides labeled for use on azaleas will provide control and oftentimes multiple applications are necessary. For optimal coverage, be sure to direct the spray to the undersides of the leaves. Using a recommended systemic insecticide drench in spring could prove to be a season-long remedy.
Starting March through August, the Alabama Cooperative Extension System offers a Gardening Helpline for the general public each Monday through Thursday from 9 a.m. until 1 p.m. This helpline is operated by Master Gardener volunteers who use research-based information to best answer all of your gardening questions.
Mallory Kelley is a regional Extension agent specializing in home grounds, gardens and home pests.