• Topics: Environmental Horticulture  | Shrubs and Trees (MG, South Florida ed.)  | Shrubs and Trees (MG, North and Central Florida ed.)  |  Crapemyrtle  |  Knox, Gary W 

Crape Myrtle in Florida¹

Crape myrtle (Lagerstroemia species) has become a dominant landscape plant in north and central Florida and throughout the South. Breeding programs over the last 30 years have produced superior forms with a wide range of plant sizes and habits, improved flowering, new flower colors, ornamental bark, ornamental foliage, disease resistance and increased vigor. Its remarkable success as a landscape plant is largely due to the widespread usage of hybrid L. indica × fauriei cultivars.

History and Taxonomy

Lagerstroemia species are deciduous shrubs or trees with geographic origins in China, Japan, and other parts of southeast Asia. L. indica has been cultivated as an ornamental for centuries and was introduced to the southern United States over one hundred and fifty years ago. L. speciosa, commonly called Queen's Crape Myrtle, has been popular as a flowering street tree in tropical areas, including south Florida. L. fauriei, L. subcostata and L. limii have been used in breeding programs, and cultivars of L. indica × fauriei hybrids now constitute the most widely grown crape myrtles today. Other species of Lagerstroemia are used as timber in their native ranges in Asia.

The scientific name, Lagerstroemia, was coined in 1759 by Carl Linnaeus, who described and named the plant in honor of Magnus von Lagerstroem, an avid naturalist and director of the Swedish East Indies Company. Crape myrtle derives its common name from its crepe-like, crinkled petals, and the resemblance of its leaves to the true myrtle, Myrtus communis. "Crape myrtle" is a peculiarly-American term. Elsewhere in the world, "lagerstroemia" is often used as the common name for crape myrtle.

Characteristics

Crape myrtle is valued as a landscape plant for its prolific summer flowers, heat and drought tolerance, and year-round landscape interest. Flowering begins as early as May in some cultivars and continues into the fall. Each 6- to 18-inch cluster of flowers (or panicle) develops on the tips of new growth and is composed of hundreds of 1-to 2-inch flowers. Color ranges include shades of purple, lavender, white, pink and red, including “true” red, a relatively recent development. Some cultivars have bicolor flowers (two colors on each petal), some cultivars have flower colors that fade with age or certain environmental conditions, and other cultivars have panicles composed of a mix of flower colors.

Many Lagerstroemia fauriei and hybrid cultivars feature beautiful, colorful bark. Strips of bark peel off in early summer to reveal mottled new bark ranging in color from pale cream to dark cinnamon to rich brown to bright orange. The bark color gradually fades over winter until it peels again the next summer.

Leaves on many of the Lagerstroemia indica cultivars are rounded or spoon-shaped and up to 3 inches long. Most hybrid cultivars have lance-shaped leaves up to 5 inches long and 3 inches wide while other species have even larger leaves. Leaves are often tinged red in the spring and turn dark green by summer. Several cultivars are known for new growth that is bronze, red or burgundy and some cultivars are claimed to have burgundy-colored foliage all summer. In north Florida and northwards, foliage may turn brilliant yellow, orange or red in autumn.

When the leaves fall in winter, crape myrtle becomes a living sculpture. The trunk and branches of tree-form plants have an attractively gnarled, sinuous character with smooth bark.

Landscape Use

Crape myrtle is one of our most versatile landscape plants for sunny locations. They are available for use as medium trees, small trees, shrubs, groundcovers, container plants, large perennial bedding plants and hanging baskets. However, the most commonly available cultivars are best used as small trees in Florida.

For best results and minimum maintenance, choose a cultivar whose growth characteristics and ultimate size fit your intended landscape use. Misplacement of a shrub- or tree-like crape myrtle will require you to prune it constantly to keep it from outgrowing its place. Single- or multi-stemmed tree-form crape myrtles are ideal as flowering specimen trees or as small, flowering shade trees near patios, walkways, and entrances. Shrub forms make an excellent accent in a shrub border when planted in groups. Dwarf plants are effective as large groundcovers, perennial bedding plants, or container plants providing vivid, summer-flowering interest. Some dwarf crape myrtles are used in hanging baskets.

Background plantings of evergreens emphasize the floral display of crape myrtles. Dark colored mulches or dark green groundcovers highlight the ornamental characteristics of crape myrtle trunks and bark.

General Culture

Crape myrtle is adapted to climatic conditions throughout Florida. Well-established plants are extremely drought tolerant and have low fertility requirements, although they respond to fertilizer and water with lush growth. Crape myrtle has low salt tolerance, so it should not be irrigated with saline water or used near the coast unless it is well-protected from saline conditions.

Full sun is necessary for best flowering and for development of a full, symmetrical crown. Crape myrtle is tolerant of a wide range of soil types but grows poorly in wet soils. It is best adapted to loamy soils that are slightly acid (pH 5.0 to 6.5). Species and cultivars susceptible to powdery mildew should be placed in locations that allow air movement to help avoid potential problems with this unsightly disease.

Crape myrtle transplants easily. Best results occur if container-grown crape myrtles are planted during early summer when in active growth. Bare root or balled-and-burlapped crape myrtles should be moved and planted while dormant. Plants should be mulched to a depth of 3 inches.

Newly planted crape myrtle should be irrigated regularly for the first few weeks to aid in establishment. Trees with a trunk diameter greater than 1 inch benefit from regular irrigation for several months. Crape myrtle is very drought tolerant once established but moist soil or irrigation promotes growth. Fertilization will stimulate growth of young crape myrtles but established crape myrtles usually do not need fertilizer because root systems extend into lawns where they can absorb nutrients from applications of lawn fertilizers.

Young crape myrtles characteristically develop multiple stems. If a crape myrtle is to be grown as a small tree, the smallest stems should be removed, leaving one main stem for a single-trunk specimen or 3 to 5 main stems for a multi-trunked tree.

Crape myrtle generally requires little pruning. "Suckers" or water sprouts may develop along the lower portions of main stems or from roots. These should be removed when using crape myrtles as trees. Small twiggy growth on disease-susceptible shrub and tree forms should be thinned out from underneath and within the canopy. This keeps the trunk clean to allow air circulation and help prevent powdery mildew disease. Dwarf crape myrtles periodically grow tall shoots that must be removed to maintain the planting as a groundcover. Shoots of some dwarf cultivars occasionally die to the ground over winter, and dead wood should be removed in the spring.

If pruning is necessary to improve plant shape or form, prune crape myrtle anytime after the leaves have fallen. However if plants are pruned too early in the fall, new growth may emerge and be killed by the first freeze. Plants are easy to prune while dormant since the branch structure is readily visible without foliage. Pruning while plants are dormant also will not interfere with flower bud formation since crape myrtle flowers form on new growth. Avoid annual or frequent hard pruning. Severe pruning can induce excess vegetative growth, basal sprouting, and fewer, but larger, flower panicles. It also spoils the beautiful winter branch structure on crape myrtle trees.

Tip pruning to remove old flower clusters will promote recurrent blooming but is not practical for large plants or low maintenance landscapes. Tip pruning is largely unnecessary on many newer cultivars that naturally repeat-bloom, but tip pruning may enhance recurrent bloom of older L. indica cultivars.

Pests

Crape myrtle can be one of the most pest-free landscape plants with proper cultivar selection and with proper siting. Primary pests in Florida are powdery mildew and the crape myrtle aphid with its associated sooty mold.

Powdery mildew is caused by the fungus Erysiphe lagerstroemiae. It first appears on new shoots as a whitish powder that later spreads to the surface of leaves, stems, and flowers (a black powder on leaves is caused by sooty mold; see the section on "crapemyrtle aphid"). Powdery mildew causes leaves, stems and flowers to become distorted and stunted. In severe cases, leaves may drop prematurely and flower buds may fail to open properly. Shady, humid locations and cool nights encourage powdery mildew as does frequent wetting of the foliage by irrigation or rainfall. Powdery mildew is more prevalent in spring and fall.

The best way to avoid powdery mildew is to plant one of the cultivars bred and selected for resistance to powdery mildew (See Table 1). Additionally, crape myrtle should be planted in sunny locations allowing free air movement so that wet foliage dries quickly.

Crapemyrtle aphid, Tinocallis kahawaluokalani, was apparently introduced into the United States with crape myrtle, its host plant. Crapemyrtle aphids are pale yellow in color with winged adults having black wings and black protuberances. They primarily are found on undersides of leaves and are particularly attracted to new growth. Crapemyrtle aphid is not found on any other commonly grown plant. No aphid species other than crapemyrtle aphid infest crape myrtle.

These insects damage crape myrtle by inserting mouthparts into soft tissue and extracting plant sap. Crapemyrtle aphids can reproduce and develop large numbers rapidly. Heavy infestations distort leaves and stunt new growth.

In north Florida, crapemyrtle aphid populations generally peak between late June and early August. Crape myrtles should be inspected regularly during this period to monitor populations of aphids. Aphid populations can probably be managed if control measures begin by the first week of July. Elsewhere in Florida, one or more population peaks may occur at any time between May and September. Although many predatory insects feed on crapemyrtle aphids, they usually cannot control the aphids. Sprays of insecticidal soaps or horticultural oils are the most environmentally safe pesticides for controlling crapemyrtle aphids.

During feeding, aphids secrete droplets of a sugary solution called "honeydew." Drops of honeydew fall from the aphids onto leaves and stems below. This sugary solution promotes the growth of sooty mold fungi, Capnodium species. Sooty mold appears as a black staining or powdery coating on leaves and stems (a whitish powder on leaves is symptomatic of powdery mildew; see "powdery mildew"). The blackened leaves and stems are often the most obvious sign of aphid infestation.

Although unsightly, sooty mold itself does not directly harm crape myrtle. However, the black fungus shades the leaves and interferes with photosynthesis, potentially reducing the long-term vigor of the plant. Control of crapemyrtle aphid will halt further development of sooty mold. Existing sooty mold on leaves will wear off the leaves through the actions of sun, rain, and wind. Sprays of insecticidal soaps and horticultural oils for control of crapemyrtle aphid also help to loosen and remove sooty mold.

Secondary pests of crape myrtle include metallic flea beetle (Altica species), Florida wax scale (Ceroplastes floridensis), Cercospora leafspot (Cercospora lythracearum) and mushroom root rot (Armillaria tabescens).

Propagation

Crape myrtle can be propagated vegetatively by softwood, semi-hardwood, hardwood, or root cuttings. Softwood and semi-hardwood cuttings root easily when taken in spring or summer. Hardwood cuttings from dormant plants also root easily, although use of rooting hormone improves rooting percentages. Root cuttings may be dug in early spring and planted in the greenhouse. Root cuttings root inconsistently.

Seed capsules ripening in the fall may be collected, dried, and stored in sealed containers. No seed pre-treatment is necessary and seeds will germinate within 3 weeks after sowing. Best growth results when seeds are sown during the lengthening days of spring. Flower, bark and growth characteristics of crape myrtle seedlings vary tremendously.

Cultivars

Many cultivars of crape myrtle have been developed by private individuals, nurseries and public institutions. In 1962, the U.S. National Arboretum in Washington D.C. began a crape myrtle breeding project with Lagerstroemia indica. Major advances occurred when L. subcostata and L. fauriei were introduced into the breeding program in 1966. The resulting hybrids were highly ornamental and resistant to powdery mildew. As a result of the late Dr. Donald Egolf's efforts, the U.S. National Arboretum has released over 24 selected for cold hardiness, for resistance to powdery mildew, and for varying heights, habits, flower colors, fall foliage colors, and bark characteristics. All U.S. National Arboretum cultivars have Native American names.

The U.S. National Arboretum is continuing Dr. Egolf's work, and many other individuals also have joined the ranks of crape myrtle breeders. Dr. Carl Whitcomb, Dr. Michael Dirr and Dr. Cecil Pounders currently operate prominent crape myrtle breeding programs. Evaluations of these and other cultivars are under way at the University of Florida/IFAS North Florida Research and Education Center in Quincy to determine the best cultivars for Florida conditions. Cultivar descriptions and observations from these crape myrtle cultivar evaluations are listed in Table 1.

References

Byers, David. 1999. Personal communication. Byers Nursery Company, Inc., Huntsville, AL.

Byers, David. 1997. Crapemyrtle: A Grower's Thoughts. Owl Bay Publishers Inc., Auburn, AL.

Davy, John. 1999. Personal communication. Panhandle Growers, Inc., Milton, FL.

Dirr, Michael A. and Charles W. Heuser, Jr. 1987. The Reference Manual of Woody Plant Propagation. Varsity Press, Inc., Athens, Georgia. 239 pp. Pp. 144-145.

Egolf, Donald R. and Anne O. Andrick. 1978. The Lagerstroemia Handbook/Checklist. American Association of Botanical Gardens and Arboreta, Inc. 72 pp.

Knox, Gary W. and Jeffrey G. Norcini. 1991. "Lagerstroemia cultivars under evaluation at the NFREC-Monticello." Proc. Fla. State Hort. Soc. 104: 346-347.

Mizell, Russell F., III and Gary Knox. 1993. "Susceptibility of crape myrtle, Lagerstroemia indica L., to the crapemyrtle aphid, Tinocallis kahawaluokalani (Kirkaldy) in north Florida." Journal of Entomological Science 28(1): 1-7.

Pooler, Margaret and Ruth Dix. 1999. Personal communication. U.S. National Arboretum, Washington, D.C.

Westcott, Cynthia. 1971. Plant Disease Handbook, third edition. Van Nostrand Reinhold Company, New York. 843 pp. Pp. 293-298 and 405-406.

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. Millie Ferrer-Chancy, Interim Dean.

• Copyright 2009 |
• Site Feedback |
• About This Site