M is for Myrtle, Not Murder
By Nicholas Hansen
Certified Arborist License #- PN-9090AU
July 4th, 2021
Crape myrtle (Lagerstroemia) is a flowering ornamental tree with around 50 different species and hundreds of individual varieties. They can range from one foot tall to over one hundred feet tall, however, most are small to medium-sized and have multiple trunks. Commonly found in gardens and yards across the southern and western United States, crape myrtles have highly desirable flower and bark displays. The roots are considered non-destructive to nearby structures and they are relatively easy to care for.
As many owners may know, the flowers are only on the new growth. This has led to a widespread misconception that pruning is required in order to promote new growth and thus flowers. Countless healthy trees have been needlessly topped in an effort to either control the height of the tree or to promote flowering. In fact, this practice is so common that it has its own name. Crape Murder. One of the many benefits of having a crape myrtle is that they require little to no pruning so long as the right tree is planted in the right place. Encouraging the shape of the tree is the majority of any pruning a crape myrtle needs. Severely reducing its height is an exercise in futility that will bring a myriad of problems along with it. Pests and diseases are all too eager to invade a crippled tree and that’s when a low maintenance tree becomes high maintenance.
Although beautiful, these trees have been improperly pruned and are susceptible to disease and insect infestation.
This picture shows that branches have been topped where a branch does not meet another branch, and is thus unable to compartmentalize the wound.
After topping, the tree uses its emergency reserves to send up new foliage called epicormic growth. These new sprouts will bring lots of flowers with them since the flowers are produced on new growth. Unfortunately, these sprouts are very weakly attached to the stem from which they came and often can’t support the weight of the flowers they produce. All the excess new growth has extra sugars which attract aphids, who extract sap from the leaves and excrete a sugary substance called honeydew. This happens to be the favorite food of many organisms which include ants, wasps, flies, and sooty mold. Ants will often move in and actually farm the aphids for their honeydew. All of these pests are symptoms. The true cause was improper pruning.
A properly trimmed Crape Myrtle can still bear many flowers.
This is the interior of the tree depicted above. Notice there are no flat nubs from pruning in the improper location
The wound caused by the initial pruning cut will often rot and can provide a perfect home for carpenter ants. A common misconception about carpenter ants is that they eat trees and will invade buildings and eat those too. These ants are actually beneficial to wounded trees because they prevent the rot from spreading. They often get blamed for damage to homes, but if carpenter ants are eating the lumber inside of a building, that lumber came from faulty wood to begin with. They need moisture and decay in order to break down wood. They do not eat the wood, they live in it. Regardless, most people don’t want these pests in their homes.
If Crape Murder has already been committed, it’s not necessarily a death sentence. It is possible to fix, however, it takes years of corrective pruning. In some cases, it may be better to cut the tree off at ground level and train the new sprouts from the ground up. If the reason for the topping was to reduce the height, it is probably best to remove the tree and replace it with a variety that does not grow so tall. Having the right tree in the right place will end up not only looking much better, but will be far less costly.
Another example of a properly pruned Crape Myrtle.