Crape myrtle (Lagerstroemia indica) is one of the most useful flowering shrubs grown in southern states, said David Trinklein, state horticulture specialist for University of Missouri Extension. It is long-lived, withstands droughts and is relatively free of disease and insect problems.
It also adds brilliant color to the landscape when few other trees or shrubs are in bloom.
While older cultivars lacked the cold-hardiness needed to survive Midwestern winters, breeding work has resulted in crape myrtle cultivars with better cold tolerance and disease resistance, improved flower and fall leaf color and more handsome bark, said Trinklein.
For strong growth and abundant flowering, crape myrtle needs full sun. Lack of sunlight and competition for moisture with large shade trees will reduce growth and flowering and increase disease problems.
Although crape myrtle can adapt to many soil conditions, it prefers a well-drained garden loam. Good drainage is important for the prevention of root diseases.
When planting crape myrtle, dig a hole at least twice as wide as the root ball. Set the plant in the hole no deeper than it originally grew in the production container or field, and backfill with the soil removed from the hole.
Research has shown that amendments to backfill soil encourages roots to stay within the hole and not grow outward into the surrounding native soil.
It is a common misconception that crape myrtles require pruning to flower. In fact, the most natural and beautiful crape myrtles result from limited or no pruning.
In addition, aggressive pruning leads to increased suckering, which is not only undesirable but could result in powdery mildew spreading from the suckers to the canopy of the plant.
It is far better to plant more compact cultivars that grow to desired mature heights than to continue fighting with larger cultivars planted in a too-small space.
Crape myrtles flower on new growth of the season, so if pruning is needed, do so in late winter to early spring before new growth resumes. Avoid pruning in early fall before the first frost, since pruning forces new growth and keeps the plant from going dormant.
Severe freezes can kill the plant if it is not fully dormant.
A complete general-purpose garden fertilizer, such as 8-8-8 or 10-10-10, is ideal for crape myrtles. To newly planted small plants, apply 1 teaspoon of fertilizer monthly from March to August along the perimeter of the planting hole.
Larger, established plants will benefit from 8-8-8 or 10-10-10 at a rate of 1 pound per 100 square feet or 12-4-8 or 16-4-8 at a rate of ½ pound per 100 square feet in spring. Avoid overfertilization, which causes excess growth and reduced flowering
Two troublesome diseases on crape myrtle are powdery mildew and Cercospora leaf spot. Powdery mildew is the most widespread and serious of the two in most regions. It typically develops in late spring and fall and is associated with warm days and cool nights along with high humidity.
Powdery mildew and Cercospora leaf spot can be controlled with fungicides when the diseases are first noticed.
However, the best approach is to plant disease-resistant cultivars. Several new crape myrtle cultivars are resistant to powdery mildew and Cercospora leaf spot. They are ideal for gardeners wanting low-maintenance landscapes.
