Crape myrtles in western Kentucky suffered partial or total kills of the top portions of the trees this spring. Trees and shrubs had lost their winter dormancy when the April 15 and 16 freeze occurred with temperatures dropping to between 27-29 degrees in this area.
Dr. Bill Fountain, University of Kentucky Arboriculture and Landscape Management Specialist, offered this explanation: “Crape myrtle is really only marginally hardy even though it survives in great shape most years. I consider it to really be a tropical species that just happens to be able to tolerate some cold.”
Some trees were killed back to the ground. Even though the cambium layer was still green, the dormant buds were also killed. In some plants there is a partial loss in the top, with a mix of dead branches and new shoots and new shoots from the ground as well.
“An abundance of shoot growth at the base of plants indicates that the crape myrtle has had a lot of damage to the conductive tissues and is trying to regenerate new growth from the base of the trunk that was not damaged,” Fountain said of the latter.
How should crape myrtles that are trained in a tree form be pruned?
The first option is to remove the shoots at
the base of the trunk if they are not what the owner wants as a form for their crape myrtle.
If all the shoots are allowed to grow the form will be a crape myrtle bush. Removing new ground shoots will encourage shoot growth in the upper portions of the tree.
Pruning out the deadwood in the top of the tree at this point will probably not help or hurt the overall health of the plant. However, it would allow the person doing the pruning to cut the damaged branches back to the more healthy, vigorous shoots. This will probably be tedious and would necessitate somebody standing on a ladder.
Even if the pruning does not occur these shoots will eventually become dominant. There may be additional dieback of branches that would need to be cut back at a later date. Pruning out dead wood will make the plant look better and allow for monitoring to see if the plant continues to decline.
Many of the crape myrtles have developed significant vertical cracks on the trunk. This indicates significant damage to the cambium.
A second option for pruning to a tree form is to cut the old trunks to the ground while saving the strongest laterals as the new shoots. Gradually thin these to the strongest shoot. The new shoots that are kept will get tall rapidly and have a straight trunk. Owners will have the option of leaving one
or multiple trunks depending on their aesthetic preferences.
Susan Fox is the Lyon County Extension Agent for Agriculture and Natural Resources.