Crape Myrtle Culture (C 944)Download PDF
Crape myrtle (Lagerstroemia indica) is one of the most useful flowering shrubs/trees grown in Georgia. It provides abundant summer color with a minimum of maintenance. Because of these features, crape myrtle should be used more often in the home landscape and as street trees in community developments. Crape myrtle is ideally suited for community plantings since it is long-lived, withstands droughts after becoming established, and is relatively free of disease and insect difficulties. Colors range from red and pink to lavender and white. It is usually best to use only one color in each cluster. Crape myrtle can be used effectively with other summer flowering shrubs, such as althea, if you exercise care in harmonizing colors.
During recent years considerable breeding work has resulted in a number of new crape myrtle cultivars (See Table 1). Plant height ranges from less than 3 feet to more than 20 feet, making it one of the most versatile plants. Some cultivars can be used as small foundation shrubs while others as specimen trees. Many of the newer cultivars also have improved flower color, better fall leaf color, handsome bark and better cold and disease resistance than the old seedling types.
Crape myrtle will grow under adverse soil conditions. It grows and flowers much better in well-prepared soil, however, so good soil preparation is well worth the effort involved. Preparation includes digging a large hole — at least two times wider than the root ball. Set the plant in the hole no deeper than it originally grew in the container or field. Then backfill with the same soil removed from the hole after breaking apart clods and removing rocks or other debris. Research has shown that organic matter amendments are not necessary when planting in individual holes. Amendments in the hole encourage roots to stay within the hole and not grow outward into the surrounding native soil. Amendments are most beneficial, therefore, when they are incorporated uniformly throughout the soil surrounding the planting hole.
After planting, water thoroughly to settle the soil around the roots, and mulch to conserve moisture, reduce weeds and insulate the roots against extreme cold and heat. Three to five inches of pine straw, pine bark, shredded hardwood mulch or shredded leaves placed over the planting hole is ideal. Mulching a larger area beyond the planting hole is even better.
Water crape myrtle plants thoroughly at planting time and once a week, in the absence of rainfall, for the first two months after planting.
Established crape myrtle plants will tolerate drought. Flowering is enhanced, however, if plants are watered during dry periods that occur during the flowering season.
For strong growth and abundant flowering, plant crape myrtle in full sun. Heavy shade will reduce growth and flowering and will increase disease problems such as sooty mold on the foliage and powdery mildew on the flower buds and young growth. Large shade trees will also compete with the crape myrtle for moisture, causing poor growth and flowering. Lack of sunlight and moisture are the common causes of poor growth and flowering.
Crape myrtle flowers on new growth of the season, so you can prune plants any time during the late winter or early spring before growth begins without loss of flower buds. Avoid pruning in early fall before the first frost, because pruning forces new growth and keeps the plant from going dormant. Severe freezes can kill the plant if it is not fully dormant.
Pruning results in an abundance of new shoots that form flowers. It also reduces the amount of vegetative growth and funnels the energy of the plant into new growth and flowers. Pruning, however, is not essential for flowering. Some of the most spectacular floral displays can be seen on old, unpruned crape myrtles along roadsides. Flower clusters are usually smaller on unpruned crape myrtles, but the number of flower clusters is greater. Therefore, the overall floral impact of the plant is not reduced.
On some cultivars, pruning to remove spent flower blossoms after they fade will stimulate new growth and another blossom flush in late summer. A second bloom is sometimes difficult to force on cultivars that bloom after mid-July.
The type and amount of pruning that should be done each year depends entirely on desired shape and size. On large old crape myrtles, heavy pruning may not be advisable, since the tree form is the desirable feature. Crape myrtles in tree form make wonderful accent plants or specimen trees. Many cultivars develop attractive trunks with exfoliating bark that add interest to the winter garden (see Table 1).
To develop a tree shape, select three to five nicely spaced shoots growing from ground level as the main trunks. Then remove side branches from these shoots about halfway up their height. As the plant grows taller, more lower branches can be removed each year so the canopy begins 3 to 4 feet above ground level. You may also need to remove suckers (new young succulent spouts that grow from the base) periodically in order to maintain the desired tree shape. Some landscapers apply a synthetic plant growth regulator, called NAA (naphthalene acetic acid), to suckers after pruning to prevent them from resprouting.
Some gardeners prefer growing crape myrtle as a compact shrub instead of a tree. To get these results, prune the stems back to approximately 6 inches above ground level each year. Severe pruning will not kill or injure a healthy plant. Prune before growth begins in the spring. The result will be an abundance of new flowering shoots.
If an intermediate size of shrub is desired, prune moderately by removing the
twiggy growth smaller
than pencil size. This annual pruning will stimulate more vigorous growth in the spring.
When pruning, remember that new growth will emerge 3 to 4 inches below where the limb is cut. Avoid cutting back large limbs and leaving stubs, because an abundance of new growth will emerge near the cut, looking like pom-poms on stalks. Not only is this unnatural in appearance, but this thick, dense growth will be more susceptible to aphids. In the landscape industry, this type of pruning is jokingly referred to as "crape murder."
A complete general-purpose garden fertilizer — such as 8-8-8, 10-10-10, 12-4-8 or 16-4-8 — is ideal for crape myrtle. To newly planted small plants (1-gallon size), apply 1 teaspoon of fertilizer monthly from March to August along the perimeter of the planting hole. Larger, established plants will benefit from one broadcast application of fertilizer in spring. Apply 8-8-8 or 10-10-10 at a rate of 1 lb. per 100 sq. ft. or 12-4-8 or 16-4-8 at a rate of ½ lb. per 100 sq. ft. Avoid over-fertilization because it causes excess growth and reduced flowering. The best time to fertilize is just before a rain. Otherwise, water in the fertilizer after application with irrigation. It is not necessary to remove mulch when fertilizing.
Crape myrtle is easily propagated from semi-hardwood cuttings taken during the growing season. June, July and August are excellent times to root cut-tings. Take cuttings from new growth of the season, leaving three to four nodes per cutting and several leaves. Rooting hormone is generally not necessary, and cuttings should root in three to four weeks. Place cuttings in a well-drained rooting medium in a shaded area and keep them moist by enclosing them in a clear plastic bag.
Cuttings also can be placed in prepared outdoor rooting beds. Thoroughly cultivate the soil to a depth of 10 to 12 inches. Add 4 to 5 inches of organic matter such as peat moss, leaf mold or pine bark to the surface and thoroughly mix it into the soil.
Place the cuttings approximately 6 inches apart. Insert them one-half their length into the soil. Mulch with 2 to 3 inches of pine straw, leaf mold or pine bark to conserve moisture. Keep them moist with regular misting.
The young rooted plants can be transplanted to their permanent location during the fall and winter.
Several diseases occur on crape myrtle including powdery mildew, Cercospora leaf spot, root rot and sooty mold. Powdery mildew is the most widespread and serious disease in Georgia. Powdery mildew typically develops in late spring and fall and is associated with warm day and cool night temperatures and high humidity. Leaves, young shoots and flowers are heavily coated with a powdery, white mold that can distort new growth. Infected flower buds may not open, and severely infected leaves and buds often drop early.
The other most damaging disease is a leaf spot caused by the fungus Cercospora lythracearum. Spots develop in mid-summer through fall during wet, humid weather. Large, dark brown spots develop on lower leaves and progress upward through the plant. Infected leaves turn yellow around the spots and drop prematurely. Sometimes even one spot will cause a leaf to drop on susceptible cultivars and can cause significant defoliation prior to frost.
Powdery mildew and Cercospora leaf spot can be controlled by applying fungicides when the diseases are first noticed. Consult the Georgia Pest Control Handbook for current fungicide recommendations. The best approach to prevent diseases is to plant disease resistant crape myrtle cultivars. A number of new crape myrtle cultivars from the U.S. National Arboretum and other nurserymen are resistant to powdery mildew and Cercospora leaf spot. (See Table 1) They are ideal for gardeners wanting low-maintenance landscapes.
Sooty mold is an unsightly superficial, dark brown or black coating on leaves and stems that can be removed by rubbing. It is the result of a fungus growing on honeydew excretions made by insects such as aphids, which are the most serious insect pest on crape myrtle. Sooty mold usually causes little direct damage, but it can cut vigor by reducing photosynthesis in the leaves. Using crape myrtle aphid-resistant cultivars and insecticide sprays can reduce sooty mold.
Root rots can be prevented by growing plants in well-drained soil.
|Table 1. Partial list
of popular crape myrtle cultivars by height
|Indicates the cultivar is a release from the U.S. National Arboretum.|
|Indicates the cultivar has shown resistance to Cercospora leaf spot in field trials.|
|Dwarf (3 to 5 ft.)|
|Cultivar Name||Flower Color||Mildew Resistance||Exfoliating Bark|
|Baton Rouge||Deep Red|
|Bayou Rouge||Deep Red|
|Bourbon Street||Watermelon Red|
|Chica Pink||Bright Pink|
|Chica Red||Rose Red|
|Petite Embers||Red Rose|
|Petite Orchid||Dark Orchid|
|Petite Pinkie||Clear Pink|
|Petite Plum||Deep Plum Purple|
|Petite Red||Deep Crimson Red|
|Pocomoke||Deep Rose Pink|
|5 to 10 Feet|
|Prairie Lace||Pink w/white||Fair||Average|
|Velma's Royal Delight||Magenta||Good||Average|
|10 to 20 Feet|
|Centennial Spirit||Dark Red||Good||Average|
|Near East||Light Pink||Moderate||Average|
|Raspberry Sundae||Pinkish red w/white||Fair||Average|
|Regal Red||Dark Red||Good||Average|
|Royal Velvet||Bright Pink||Good||Average|
|Wm Toovey||Pink Red||Good||Average|
|20 feet or more|
|Basham's Party Pink||Light Lavender||Good||Good|
|Byers Standard Red||Soft Red||Good||Average|
|Byers Wonderful White||Clear White||Good||Average|
|Carolina Beauty||Dark Red||Poor||Average|
|Hardy Lavender||Medium Lavender||Good||Average|
|Red Rocket||Bright Red||Good||Average|