Crape myrtles (Lagerstroemia indica) are small trees grown for their colorful flowers and unusual bark. These deciduous plants grow in U.S. Department of Agriculture plant hardiness zones 7 through 9, where summers are hot and winters are mild. Crape myrtles bloom for weeks from spring through summer. Judicious pruning encourages large, full flower clusters.
Crape myrtles bloom best in full sun and well-drained soils. From miniature myrtles, less than 3 feet high, to landscape trees up to 20 feet high, crape myrtles develop flower clusters at the ends of the branches in colors of white, pink, lavender or red. When the full, showy clusters fade, seed pods form at the branch ends. Pruning the pods off promotes more flower clusters. The myrtles continue blooming until early autumn, when the branch and trunk bark naturally exfoliates, with outer bark peeling off to expose gray, tan or cinnamon inner bark.
Crape myrtles, especially small trees and shrubs, require little pruning. Because myrtles produce flowers on new growth, prune them lightly in late winter or early spring while they are dormant and before branches leaf out. For a shrub effect, leave lower branches and or suckers in place for shrub forks and trim out damaged or weak inner twigs and branches. To maintain the tree shape, prune away sucker and lower branches so that one main trunk predominates. This early spring pruning stimulates new growth that produces abundant flowering clusters.
Canopy pruning, where an all-over shearing removes the ends of branches and leaves an umbrella shape, is not suited to crepe myrtles. This results in sparse flowers and does not remove old and weak branches. Prune out damaged branches by cutting them back to a main trunk or fork. Avoid severe pruning because it results in large, heavy flower clusters that bend down the branches. These oversized clusters strain the tree and distort the shrub or tree shape.
Flowering is adversely affected by factors such as shade, fertilization or water. Shade suppresses blooming because myrtles need full sun exposure for maximum flower production. Myrtles thrive with light fertilizer and occasional water. Too much fertilization or daily watering develops foliage at the expense of flower buds. Crape myrtles are resilient. When winter appears to top-kill the tree or shrub, prune off dead branches before spring growth begins. Since myrtles produce flowers on new twigs and branches, they typically bounce back with prolific flower clusters.