Few flowering plants can compete with crape myrtles ( Lagerstroemia indica and cvs., USDA Hardiness Zones 7–9) for vibrant summer color. As an added bonus, crape myrtles thrive in heat and humidity and are drought tolerant to boot.
Though many people plant crape myrtles, few people prune them correctly. Correct pruning yields gracefully shaped trees with more blooms that are held upright on strong stems. And flowers arrive earlier than do those on unpruned or mispruned plants.
Crape myrtles bloom on new growth, so prune them in early spring before they break dormancy. Although some gardeners prune their crape myrtles in the fall, I do not recommend doing this. Fall pruning not only creates an unattractive look for winter but also removes the current year’s growth as a buffer against any potential winter damage. Good pruning while crape myrtles are young will mean less maintenance when the trees are older.
he habit of crape myrtles is to produce multiple trunks, which can cause the plant to get crowded as it matures. A healthy, well-structured crape myrtle will have only a few main trunks. Removing the unnecessary ones first means reducing the overall amount of pruning you need to do.
Maintain an attractive framework
For most crape myrtles, choose three, five, or—at most—seven main trunks. An odd number of trunks is more pleasing to the eye than an even number, which often looks like soldiers in formation. Keep trunks that have ample space to grow and are growing straight and strong.
Cut all the way back
Prune suckers and any additional trunks as close to the soil line as possible. This will avoid leaving a dead stub, which is unsightly and a potential entry for insects and diseases.
Remove low branches
I like branching to begin 6 to 8 feet off the ground because it looks better and is more practical. If you don’t need to walk under the branches or see through them to view oncoming traffic, you can allow the branching to start lower. Prune unwanted low branches all the way back to the main trunk.
Step 2: Finish at the top
A good portion of the upper branches will have been removed when you pruned out the trunks. But you still need to thin the crown to improve the tree’s looks and health.
Thin the crown
The upper branches look best if they spread in different directions, so remove any that are growing into an area already occupied by another branch. Make your cuts slightly above a bud that faces the direction in which you want your new branch to grow. Also remove limbs that cross back through the plant or rub against each other. Wind movement and growth can cause these branches to wound each other, and you will eventually lose one or both.
To allow better air circulation and sunlight penetration, which will reduce the potential for diseases like powdery mildew, remove excess branches in the interior of the plant.
Prune weak growth
Your final cuts will be to prune out any branches or stems smaller in diameter than a pencil. Leaving wood that small on the tree results in weak new growth, which will have a difficult time supporting any flowers.
The results of poor pruning
Crape myrtles have the potential to be wonderful small trees if they aren’t chopped to their knees annually. Luckily, crape myrtles are resilient and can tolerate the topping or shearing that some folks insist on giving them. Here are the downsides to pruning a crape myrtle back to an ugly 3- to 4-foot nub every year.
WEAK BRANCHES Severe pruning encourages rapid new growth (photo, right) with large flower heads. Unfortunately, the new branches are so long and weak that they can’t support the weight of the flowers. Sometimes the branches snap off under the weight.
FEWER BLOOMS Allowing too many trunks to grow or cutting the plants back too far will result in a shrubby plant whose densely packed foliage produces fewer, later blooms and is more susceptible to powdery mildew.
UNREMARKABLE BARK Shearing crape myrtles prevents the trunks from maturing enough to develop the outstanding peeling and colored bark many varieties have. This “coming of age” for crape myrtles provides as much interest in the winter landscape as the flowers do in summer.