One of the most confounding arguments I face is whether and how to prune crapemyrtles. They are mercilessly “murdered” by unaware landscapers and homeowners each winter… yet they still bloom in summer. Some people even believe a crapemyrtle won’t bloom unless it is severely pruned.
Crapemyrtles do not HAVE TO be pruned at all. They will still bloom.
In truth, a crape myrtle will forgive almost any pruning method. However, severe pruning leads to lush and rampant growth, which can exacerbate disease and insect problems.
Keep in mind that some crapemyrtle varieties will grow into trees and some varieties will only be many-branched shrubs. Knowing which variety you have will help you make the decision on how to prune.
Assuming you have a tree-form crapemyrtle, the pruning can be done in three steps:
1. Remove sprouts near the ground and along the trunk(s).
2. Remove interior sprouts that travel “crosswise” inside the top of the “tree”. Most of those you leave should be vertical or leaning towards the outside.
3. Shorten all long arching sprouts back to the point where they are one-half to one-fourth inch in diameter. You will have no dry flower heads left on the plant and it will have a nice “ice cream cone” shape – ready to bloom this summer.
If you have a shrub-form crapemyrtle, simply shape it as desired. Remember that it grows vigorously in summer. If you want it to be six feet high, prune back to 4 – 5 feet in winter to allow for new growth.
Here are two good links that describe the process:
And here’s a link to a study of how pruning affects the growth and blooming of crapemyrtles.