Azaleas for the Landscape

Most Mississippi gardens have contained an azalea at some point. Azaleas are in the genus Rhododendron, which has more than 900 species. Azaleas are native to many parts of the world, but the most colorful varieties come from China, Japan, and the eastern United States.

There are many characteristics that make the azalea a beloved plant. They flourish with beautiful blooms that can provide an array of colors from mid-spring through early summer. Many varieties also offer colorful fall foliage. With dwarf, intermediate, and large varieties available, gardeners have a wide selection to choose from.

Azaleas are hardy from USDA climate zones 5 to 9. North Mississippi is in zone 7, and the extreme Gulf Coast area is in zone 9, making azaleas hardy throughout the state. All of these attributes make the azalea an excellent plant for Mississippi landscapes.

Planting

Azaleas can be used in many ways in the landscape or garden area. They may be used as border or facer plants along a boundary, as background plantings to frame an area, as foundation plantings to build the design around, or in mass-planted groups to brighten up a landscape room.

Where to Plant

Some azaleas can grow in full sun, but most are best suited for a landscape area with partial shade. This could be on the north side of the house or in a wooded area that receives filtered sunlight through trees. They do best in an acidic soil with a pH between 4.6 and 6.0. A soil test is the best way to ensure proper soil acidity. A higher pH (greater than 6.0) results in poor growth and plants stressed by insects and disease.

Azaleas prefer well-drained soil with an abundant supply of peat moss. If the native soil is poorly drained, you should make raised beds. You can do this with landscape timbers or crossties, or by hilling the soil up 8 to 12 inches above ground level. Azaleas will not tolerate “wet feet” (roots)!

When to Plant

Most azaleas are container-grown and can be planted any time of the year. However, planting in the fall or early spring allows time for roots to establish before summer heat arrives. Plant bare-root plants during the winter dormant season.

How to Plant

Prepare a planting hole two to three times as wide as the root ball. Set plants in the hole at the same depth or slightly higher than where they grew in the nursery or container. Backfill with amended soil and water thoroughly. Adding lots of peat moss, leaf mulch, well-composted sawdust, or other compost can make the soil more acidic, if needed. Finally, mulch the planting site with 3 to 4 inches of a mulch product or 6 to 8 inches of pine straw. Taper the mulch or straw to only 1 inch deep at the base of the plant.

Fertilizing

Have the soil tested and follow the fertilizer recommendations provided. If your soil has not been tested, apply 2 to 4 pounds of an acid-based fertilizer with a 2-1-1 ratio per 100 square feet of bed area. Fertilize individual plants with one-quarter to one-half cup of fertilizer in a uniform circle no closer than 1 foot from the base of the plant. Fertilize in early spring and again in early summer, just after plants have finished flowering. Late or over-fertilization can result in little or no flowering, excessive vegetative growth, and possible winter damage if the plants do not harden off.

Pruning

Azaleas grow and set their bloom buds during the fall months. For this reason, prune them immediately after they have finished their spring bloom period. It is okay to wait until all the azaleas in the landscape have finished blooming to prune them all at once. The best method is to use hand-held pruners and remove only one-third of the overall plant. For more information, see Extension Publication 3589 Pruning Landscape Plants.

Variety Selection

There are azalea varieties to fit most any landscape situation. Dwarf varieties only grow to 1 to 2 feet tall, large varieties may reach 12 feet, and there are numerous varieties in between.

Three deciduous species grow natively in woodland areas of the state: Rhododendron canescens, the pink bush honeysuckle; R. austrinum, the yellow bush honeysuckle; and R. viscosum, the white swamp azalea.

Most of today’s showy azaleas are hybrids. Some of the major groups of cultivated azaleas are Indicas, Kurumes, Glenn Dale hybrids, Girard’s, Robin Hill, and the Satsukis. Varieties from the Indica and Kurume groups are grown more commonly throughout the state (see Table 1).

The Encore series of azaleas has also gained great popularity in Mississippi landscapes, with more than 25 varieties to choose from. This series is known for producing flowers in the fall, as well as in the spring. The Re-Bloom series from Greenleaf Nurseries and the Bloom-A-Thon series from Proven Winners are newer releases that should perform well here as well. However, these are newer cultivars that have not been fully tested for adaptation to all of Mississippi (Table 2).

Color and Flower Forms

Azalea flowers come in a range of colors, including white, yellow, orange, scarlet, crimson, and purple. There are vivid sparkling shades, pastel tints, and pure whites. Some even have striped or flecked flowers.

The single-flower varieties have five petals with five to ten stamens. Other varieties may be double, semi-double, or the hose-in-hose (funnel) type. Azaleas flower abundantly, and, if you choose the right varieties, you may have flowers for up to 3 months (see Table 1).

Watering

Azaleas have an extremely fibrous root system that stays relatively shallow. A good watering schedule is essential during the growing season. Azaleas need the equivalent of 1 inch of rain every 7 to 10 days. It is best to water as deeply and infrequently as possible. The timing and amount will depend upon the soil type and drainage. For more information, see Extension Information Sheet 1670 The Plant Doctor: Watering and Plant Disease.

Common Diseases and Pests

Petal blight

Flowers become spotted and water-soaked and cling to the plant after they die. It is more severe in cool, moist springs. Remove old mulch and replace it. Drench or spray with a fungicide. Unless you have a “hot” compost process, do not compost this material. Remove it well away from the property.

Leaf gall

Pale green or whitish, fleshy galls with curled or deformed leaves. Occurs more in cool, moist weather. Hand-pick and destroy affected leaves. Start spraying at the end of the bloom period and continue at 2- to 3-week intervals until mid-June.

Leaf spots

Brown/bronzed leaves, with tiny black fruiting bodies on leaves. Use a fungicide at end of bloom period and continue at 2-week intervals through growing season.

Winter injury

Entire branches turn brown and die during the growing season. Look for bark splitting near base of limbs or at ground level. Use recommended varieties and keep plants in healthy condition. Water regularly during late summer and fall.

Nematodes

Leaves turn yellow and plants are stunted. They do not respond favorably to water and fertilizer. No chemical control is available. Other conditions mimic nematode injury; collect a soil sample from root zone for nematode analysis.

Iron chlorosis

Leaves turn light green to yellow, then creamy white between the veins; but veins remain green. Caused by too-high soil pH, making the iron unavailable. Lower soil pH by adding ferrous sulfate, finely ground sulfur, or aluminum sulfate. Treat foliage with iron chelate for temporary effects.

Azalea caterpillar

Causes sudden defoliation of leaves. Usually occurs in late summer or fall and is more common in the southern part of the state. Control with foliar sprays recommended for caterpillars.

Azalea lacebug

The upper surface of leaves has a gray, coarse-stippled appearance. Underside of leaves becomes discolored by excrement and cast skins. Treat with recommended soil-applied insecticides. For heavy infestations, also apply foliar insecticides when crawlers are hatching.

Scale insects

Usually found on twigs or branches and have various colors and shapes. Some look like bits of white cotton and others are brownish. Treat with recommended soil-applied insecticides. For heavy infestations, also apply foliar insecticides when crawlers are hatching.

For more information on insecticides, see Extension Publication 2369 Insect Pests of Ornamental Plants in the Home Landscape.

Publication 3705 (POD-10-24)

Revised by Jeff Wilson, PhD, Assistant Professor, North Mississippi Research and Extension Center, from an earlier edition by David Tatum, PhD, former Extension horticulturist.