Since we have a lot of Crape Myrtles in Cypress Isles, I felt the following
article might be interesting. Note that pruning of the tips to remove old
flower clusters will promote recurrent blooming (see under General Culture).
Did you know that you can ask the Orange County Extension Office during weekdays for advice on growing or maintaining any plant in your home or garden (407-836-7570)?
Crape myrtle refers to several Lagerstroemia species and hybrids that are deciduous shrubs or small trees with origins in China, Japan, and other parts of southeast Asia. Lagerstroemia indica has been cultivated there for centuries and was a favorite tree of Chinese emperors. Lagerstroemia indica, commonly called "Queen's Crape Myrtle" has been popular as a street tree in tropical areas, including south Florida. Other species of Lagerstroemia have been used in breeding programs, and hybrids between L. indica and L. fauriei now constitute the most widely grown cultivars today. The popularity of crape myrtle continues worldwide in appreciation of its summer flowers.
Crape myrtle was introduced to the Southern United States over one hundred and fifty years ago. 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, the common name for crape myrtle is "lagerstroemia."
Crape myrtle provides landscape interest year-round. 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 one- to two-inch red, pink, white, lavender, or purple flowers. Some cultivars have bicolor flowers (with two colors on each petal) and other cultivars have panicles composed of a mix of flower colors.
Leaves on many of the L. indica cultivars are rounded or spoon-shaped and up to 3 inches long. Most hybrid cultivars have lanceolate (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 are dark green in summer. Several cultivars are known for new growth that is bronze, red or burgundy. One new cultivar claims 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, the crape myrtle becomes a living sculpture. The trunk and branches of tree-form plants have an attractively gnarled, sinuous character with smooth bark. Strips of bark peel off (exfoliate) in early summer to reveal mottled new bark ranging in color from pale cream to dark cinnamon to rich brown to bright orange.
Crape myrtle is one of our most versatile landscape plants for sunny locations. Breeding and selection programs have resulted in plants of various sizes, shapes, flower colors, fall foliage colors, and bark characteristics. Crape myrtles are available for use as medium trees, small trees, shrubs, groundcovers, container plants, large perennial bedding plants and hanging baskets.
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-form crape myrtles 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.
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. However, 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 to 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 bur lapped crape myrtles should be moved and planted while dormant. Plants should be mulched to a depth of three 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 one inch benefit from regular irrigation for several months. Crape myrtle is very drought tolerant once established but moist soils or irrigation stimulate growth.
Established crape myrtles usually do not need fertilizer because root systems extend into lawns where they can absorb nutrients from applications of lawn fertilizers. Growth of young crape myrtles may be stimulated with up to three applications per year of one pound nitrogen per thousand square feet applied to the area within 1 1/2 to 2 times the canopy diameter.
Young crape myrtle 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 two to four 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. Tip pruning to remove old flower clusters will promote recurrent blooming but is not practical for large plants or low maintenance landscapes. Small twiggy growth on disease-susceptible shrub- and tree-form crape myrtles 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. The 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 on new growth. Crape myrtle should not be pruned hard on an annual or regular basis. 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.
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 "crape myrtle 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 means of avoiding problems with powdery mildew is to plant one of the cultivars bred and selected for resistance to powdery mildew. Additionally, crape myrtle should be planted in sunny locations allowing free air movement so that wet foliage dries quickly.
Crape myrtle aphid, Tinocallis kahawaluokalani, was apparently introduced into the United States with crape myrtle, its host plant. Crape myrtle 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. Crape myrtle aphid is not found on any other commonly-grown plant. No other aphid species infest crape myrtle other than crape myrtle aphid.
These insects damage crape myrtle by inserting mouthparts into soft tissue and extracting plant sap. Crape myrtle aphids can reproduce and develop large numbers rapidly. Heavy infestations distort leaves and stunt new growth.
In north Florida, crape myrtle 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 crape myrtle aphids, they usually cannot control the aphids. Sprays of insecticidal soaps or horticultural oils are the most environmentally safe pesticides for controlling crape myrtle 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 crape myrtle 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 crape myrtle aphid also help to loosen and remove sooty mold.
Unfortunately, crape myrtle cultivars resistant to powdery mildew appear to be more susceptible to crape myrtle aphid.
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.
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 Lagerstroemia subcostata and Lagerstroemia 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 cultivars selected for cold hardiness, resistance to powdery mildew, and for varying heights, flower colors, fall foliage colors, and bark characteristics. Evaluations of these and other cultivars are underway to determine the best cultivars for Florida conditions.