Crape myrtle (Lagerstroemia indica) is a flowering shrub that is quite common in the southern United States and on the West Coast. It is hardy in U.S. Department of Agriculture plant hardiness zones 6 through 11. While better adapted to humid areas, it will survive in arid regions with irrigation. Bark on older plants produces an interesting mottled pattern. Varieties are available that flower in various shades of white, pink, red and purple. Mature height varies from 3 to 35 feet.
Encouraging Crape Myrtle Flowering
Crape myrtle flowers on new wood. Pruning is not necessary for flower production but encourages more flowers. Crape myrtle is generally pruned in the winter to encourage new spring growth and often pruned again after the first round of flowers to encourage more new growth and late summer flowering. Cutting the plant back lightly in June will encourage this new growth. The crape myrtle will flower later in summer and will flower more profusely than if it had not been pruned.
Failure to Flower
If a crape myrtle is pruned too heavily, it will put all of its energy into producing new branch and leaf growth. Crape myrtles can survive being cut back to within 6 inches of the ground during the dormant period, but if you remove most of the active growth in June, it may not flower again until the next year. Excess nitrogen fertilization, no fertilization or under-watering may also prevent flowering.
How to Prune
The objective of pruning should be to produce a well-shaped plant with nicely spaced main trunks and to thin the center so sunlight and air can penetrate. Start by removing suckers coming from the base of the plant. Next, remove growth from the main trunk to a height of 4 feet or more. Eliminate higher branches growing toward the center of the plant, one of any two branches that cross and rub against each other and branches that do not fit the form of the plant. Always cut to a side branch or bud, do not leave stubs.
Dealing with Overgrown Crape Myrtle
Many people plant crape myrtle without knowledge of how large it can eventually become. If you have a large cultivar where a small one should be, consider limbing it up rather than cutting it back. Cutting it back to 4 feet above the ground, a common practice, will create an unsightly plant with weakly attached branches. Instead, remove all lower branches to create a muti-trunked tree form. If a main trunk is blocking a door, window or sidewalk remove that trunk, leaving others that are not in the way.