• Topics: Environmental Horticulture  | Shrubs and Trees (MG, North and Central Florida ed.)  | Azalea  | Midcap, James T  | Ingram, Dewayne L 

Azaleas for Florida¹

Spectacular flower masses and colors, plant form and evergreen foliage are among the reasons for azalea popularity. Azaleas in Florida bloom from late February to early April, depending upon cultivar and seasonal variation. Many azalea cultivars grow well in north and central Florida, but fewer are recommended for south Florida.

Azaleas enhance the home landscape in many ways. They are used in foundation plantings, in mass borders, or as specimen plants. Generally, they are better adapted to informal landscape designs due to their open, informal growth habit. Large azaleas are useful as background for lower plantings while low-growing ones are useful as foreground plantings. Mature size and form, flower size and color, season of flowering, and adaptability to specific conditions are among the criteria for proper azalea selection for the landscape.

Florida's warm winter temperatures may not provide adequate chilling for northern hybrids, resulting in sporadic flowering. Flower initiation follows spring growth, and flower bud development continues in late summer and fall. Flower bud dormancy is usually broken by exposure to temperatures below 50°F (10°C) for 4-8 weeks followed by warm temperatures. Sporadic flowering is more common in central and south Florida than in north Florida due to greater winter temperature fluctuation.

Adapted Species and Hybrids

Azaleas belong to the genus Rhododendron and most are native to eastern Asia (evergreen species) or North America (deciduous species). Over 800 selections exist today and hundreds of them are grown in Florida.

Southern Indian hybrids were introduced into the United States from Belgium in 1840. Their flowers are large (2-3 1/2 inches) and open in early spring. They display a multitude of colors ranging from white to salmon to orange-red. These hybrids grow rapidly and may reach a height and spread of 10 feet.

Kurume hybrids originated in Japan. They are often referred to as dwarf, although they may reach 4 to 6 feet in height and spread. Kurume Hybrids are hardier than southern Indian hybrids and perform well in north Florida and some areas of central Florida. Kurume hybrid flowers offer a wide array of colors in late January to mid February.

Satsuki hybrids also originated from Japan and are more dwarf than other hybrid groups. Flower color variety is vast since they sport freely. Satsuki means "fifth month" and these hybrids are late bloomers. They are adapted more to north Florida than central and south Florida.

Rutherford hybrids were developed in a New Jersey nursery around 1920 as American additions to Belgian hybrids. Many cultivars are used as forcing or greenhouse azaleas, and are adapted to protected areas in central Florida.

Pericat hybrids are traditionally greenhouse azaleas, but a few perform well in Florida landscapes. Most are thought to be hybrids of Belgium and Kurume hybrids.

Native azaleas are often called bush or wild honeysuckle. The individual florets are trumpet shaped and are usually borne in large terminal clusters. Natural hybridization has complicated their identification by producing many intermediate forms with unusual flower colors.

Selected cultivars in these hybrid groups are presented in the table. These are by no means the only cultivars or hybrids grown in Florida but are representative of azaleas in Florida landscapes.

General Culture

Azaleas perform best in areas with filtered sunlight. Their shallow root system and low tolerance to poor soil drainage make placement and care important.

Exposure

Partial shade under pine trees or strategically spaced hardwoods provides conditions for healthy growth and optimum flowering. Dense shade reduces plant growth and flowering. Azaleas exposed directly to early morning sun after a hard freeze are susceptible to cold injury. Rapid thawing of frozen twigs and branches may result in bark splitting. Death of branches with split bark may not occur until weeks or months after the injury.

Soils

Well-drained, organic soils with a pH of 4.5 to 5.5 are best suited for azaleas. Organic amendments and fertilization are usually necessary to modify Florida soils for proper azalea growth. Organic amendments, fertilizers, and pH-adjusting amendments should be incorporated into the planting bed or soil backfill during planting. Preparation of the entire planting area is best when a number of azaleas are being transplanted together. Organic amendments such as peat, compost or pine bark are beneficial in increasing water and nutrient retention, and lowering the soil pH. A soil test will determine the pH of your existing soil and provide a basis for fertilizer recommendations.

Ample quantities of iron and other micronutrients may not be available in soils with a pH higher than 5.5. Soils with a pH higher than 5.0 can be modified by applications of elemental sulfur. Excessive rates will injure plant roots, therefore no more than 1 pound of sulfur per 100 square feet of planting should be applied at one time. Apply sulfur no more than two or three times a year. Dolomitic lime should be incorporated to raise the pH of soils with a pH lower than 4.5. Soil adjustment should be made based on a recent soil test.

Transplanting

The planting hole for containerized or balled and burlapped azalea plants should be approximately 6 inches deeper and 12 inches wider than the root mass. An organic amendment such as peat, composted leaves, or pine bark can be incorporated into the backfill soil at a rate not to exceed one-third volume by volume. Plants should be spaced according to mature size of the cultivar but generally 3 to 5 feet apart.

Azaleas should be planted at or above the depth at which they grew in the container or nursery. An organic mulch applied to a depth of 2 to 3 inches will conserve water and reduce weed problems. November to February is the best season for transplanting; however, containerized azaleas may be transplanted any time if proper care is provided.

Watering

Irrigation is necessary for optimum plant growth during extended dry periods. Plants transplanted during the dry season into sandy soils may require watering of the root mass twice a week. Generally, established plants should be watered every 10 days to 2 weeks during dry periods to wet the soil to a depth of 14 to 18 inches.

Fertilization

Frequent and light applications of fertilizers are necessary in Florida's sandy soils. Acid-forming fertilizers like 12-4-8 or 15-5-15 should be applied in the spring, summer, fall, and winter. Apply approximately 1/4 pound to a mature plant, or 3/4 to 1-1/2 pounds per 100 square feet.

Micronutrients should be applied routinely. Complete fertilizers containing micro-nutrients are available and can be used for normal fertilization. Soil and/or foliage application of only micronutrients have proven satisfactory, although soil treatments usually have a more long-term effect.

Pruning

Pruning is necessary to obtain a full, well-branched azalea. Several light prunings early in the active growing season will result in compact growth and numerous branches on the present season's growth. Terminal vegetative growth stops after flower initiation and subsequent bud development. Pruning after flower bud initiation will decrease the number of spring flowers. Therefore, established plants should be pruned shortly after flowering.

Propagation

Evergreen azaleas are usually propagated by cuttings to maintain hybrid characteristics. Azalea cuttings are rooted most successfully when they are taken after the spring growth has hardened or matured (June). Cuttings 3 to 4 inches long have proved satisfactory. Deciduous azaleas are usually propagated by seed or layering because cuttings are difficult to root.

Pests

Diseases

The most common diseases reported on azaleas include petal blight, leaf gall and various azalea declines. Petal blight is most severe during cool, moist weather. Infection first appears as small, white spots on colored petals or rust-colored spots on white flowered varieties. Spots enlarge rapidly into irregular blotches under moist conditions, causing the blossoms to "melt" into a slimy mass. Affected blossoms dry and may remain or drop from the plants. The fungus survives in dried blossoms on or in the soil. Removing and burning surface mulch and dead flowers 3 to 4 weeks before bloom will reduce disease incidence. Directed ground sprays of a recommended fungicide one month before bloom will provide some control.

Leaf gall occurs during wet spring months and is most severe on densely shaded plantings with poor air circulation. Galls may occur on leaf, stem or flowers. Small numbers of galls can be handpicked and destroyed at first appearance. Large plantings should be protected by fungicide sprays starting at budbreak and continuing every 10 days as needed.

Azaleas decline for various root-related reasons such as root rot diseases or nematode injury. Plants that exhibit stunting, chlorosis and die-back symptoms should first be examined for problems with planting depth, soil pH or drainage. Plants in poorly drained sites often develop Pythium- or Phytophthora-caused root rot diseases. Feeder roots become mushy and discolored and the outer root layer (cortex) characteristically sloughs off when handled, leaving the string-like root center (stele).

Mushroom root rot often kills azaleas, especially those planted in sites with tree stumps or buried organic debris. The causal fungus will be visible as white mycelium under the outer bark layer of the crown or major roots.

Slow decline in plant vigor with general stunting may be due to nematode injury of the root system. Root examination will reveal galls or swellings, necrosis of fine roots, and/or general stubbiness of small roots, depending on the nematode involved. Controls for both nematode and root rot diseases are primarily preventive. Dead or dying landscape plantings should be removed with as much of the root system as possible, and the soil should be sterilized before replanting.

Insects

Lacebug, white fly, leafminers, spider mites, scale and stem borers are the most common insects that attack azaleas. Lacebugs are sucking insects found on the underside of the leaf. The top surface of the injured leaf appears speckled or mottled. Two applications of recommended insecticides at 10-day intervals sprayed on the lower surface of the leaf effectively control lacebug.

Leafminers or leafrollers feed on azalea leaves during their larval stage. Two applications of a recommended insecticide at 7- to 10-day intervals will control leafminers. Leafrollers can be controlled by two applications of a labeled insecticide at 14-day intervals.

Spider mite injury appears as a bronzing or rusty coloration of green leaves. A mite infection can be verified by placing a white piece of paper beneath the foliage and slapping the leaves with your hand. Mites can be detected on the white paper as moving, small red or brown specks. Two applications of a recommended miticide at 5- to 7-day intervals will provide acceptable control.

Several species of scale insects can be found on azaleas. Some have a white cottony appearance; others are covered with a hard shell. Scales suck the sap from azaleas, resulting in yellow or unthrifty leaves. Two foliar applications of a recommended insecticide at 2-week intervals applied during early stages of scale development provide adequate control.

Stem borers in the larvae stage tunnel into stem and branch tips during late spring and early summer. The young stem will wilt and die back to where the tunnel ends. The best way to control stem borers is to remove infested branches and then apply a properly labeled insecticide. Fungicide and insecticide recommendations are available through your county extension office.

Tables

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.

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