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Prune crape myrtles the right way

News Release Distributed 12/12/14

By Allen Owings

LSU AgCenter horticulturist

HAMMOND, La. – It’s late fall in Louisiana, and this is the time when people think about pruning plants in the landscape. One of the most commonly pruned plants in Southern landscapes is the crape myrtle. It is also the main plant in Southern landscapes that is pruned incorrectly.

As we say each year, crape myrtles need only occasional pruning to obtain the desired landscape effect. But many times these plants are pruned incorrectly because, we assume, home gardeners and industry professionals do not know the right way to prune them and do not realize the consequences of improper pruning.

An unfortunate trend in crape myrtle pruning is to "lop off the tops," which results in a crew-cut appearance. The lush growth that occurs at these cut sites appears vigorous but is actually structurally weak and is more susceptible to fungus diseases such as powdery mildew. Worse yet, when pruning is done improperly over several seasons, unsightly large, swollen knobs form at the pruned locations. Some folks refer to this pruning method for crape myrtles as “crape murder.” Southern Living magazine even hosts a “crape murder” photo contest each spring.

While crape murder does not actually kill a tree, why are these most popular, small, flowering trees pruned this way?

The method of cutting back the main branches of a tree to the same spot every year is called pollarding. This pruning method is used on some types of trees in certain situations and tends to be more common in Europe than America. But it’s not appropriate for crape myrtles.

A gardener should understand, however, that the life of a crape myrtle is shortened and the natural beauty of the tree is destroyed by this pruning technique. If gardeners understand this and still decide pollarding creates the appearance they desire for their trees, well, that’s their choice.

We often encounter gardeners who think they are supposed to prune their crape myrtles that way. Nothing could be further from the truth. For the overwhelming majority of us, the only appropriate pruning is to enhance the natural shape of our crape myrtles.

Some gardeners have been told that crape myrtles need to be pruned that way to bloom well. This is not accurate. The flower clusters may be larger on pollarded trees, but the added weight on the ends of long branches causes them to bend over awkwardly, especially after rain. And because the tree is smaller, it actually produces fewer flower clusters.

A wide selection of crape myrtle varieties is available today. Some grow tall and upright like a vase, while others are shorter and spreading, having more of an umbrella or cascading affect. You cannot make an upright-growing crape myrtle grow into other shapes by cutting it back. The new growth will simply grow upright again. So if you want a crape myrtle that will mature in the shape you desire, make sure you choose one that naturally grows that way.

Many gardeners cut back crape myrtles that are too large for the location where they were planted. This is commonly seen in trees planted close to a house. Instead of choosing a smaller-growing variety that would be appropriate, someone planted a larger type that begins to grow into the gutter and roof.

To salvage the situation, people often begin cutting back their trees. To be effective, this has to be done every year. And again, it ruins the natural beauty of the tree. This is added work that could have been avoided by planting a smaller-growing crape myrtle in the first place.

For instance, if you want a white-flowering crape myrtle planted at the corner of your house, it would be more appropriate to select Acoma, which matures at 10 feet to 12 feet, rather than Natchez, which matures at 25 feet to 30 feet.

To prune a crape myrtle properly, first decide if it needs to be pruned at all. As with any pruning project, you must have a specific purpose in mind before you begin. If you can’t come up with a good reason to prune your tree, leave it alone. If you do see something that calls for pruning, study the tree carefully and determine what needs to be pruned to accomplish the specific purpose you’ve identified.

Examples of appropriate reasons for pruning include eliminating crossed and rubbing branches, removing low branches, removing weak, thin branches from the inner part of the tree, trimming off old seed pods, creating a shapelier tree and keeping suckers removed from the base of the trunk.

Avoid cutting back or shortening branches larger than your finger. But if pruning is needed, you may cut larger branches back to a side branch or to the trunk.

With its smooth, muscular trunks, peeling bark, filigree of leafless branches in the winter and exceptionally long blooming season in summer, the crape myrtle is rightfully popular here. Make sure you keep yours looking their best.

You can see more about work being done in landscape horticulture by visiting the LSU AgCenter Hammond Research Station website. Also, like us on Facebook. You can find an abundance of landscape information for both home gardeners and industry professionals at both sites.

Rick Bogren

Last Updated: 12/12/2014 1:58:09 PM

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