Crepe myrtles (Lagerstroemia indica) are flowering trees or shrubs that are hard to beat. The species and most hybrids are hardy in U.S. Department of Agriculture plant hardiness zones 7 to 9. They bloom profusely throughout the summer in white, or various shades of pink, purple or red, and put on a colorful show in the fall with red foliage. With hybrids available in heights ranging from 1 1/2 to 40 feet, it is easy to find one to fit in nearly any sized sunny garden, or in a container on a deck or patio. Powdery mildew and fungal leaf spot can become a problem for them, and aphids and scales may attack but, overall, these are tough trees. If your crepe myrtle is weeping, there are two possible causes. One is easy to remedy, but the other is not.
Maybe it’s Supposed to be That Way
Crepe myrtles can have a naturally-occurring weeping habit. “Osage” (Lagerstroemia x “Osage”), for instance, grows slowly to a height of 12 to 18 feet with weeping branches and blooms in pink. Cultivars, like “Baton Rouge” (Lagerstroemia “Baton Rouge”), grow to a height of only about 3 feet with weeping branches and blooms in red. If the crepe myrtle is a recent addition, it may very well be a weeping variety that was mislabeled. If the weeping habit does not fit into the landscape design, there really is no remedy for it besides digging it up and replacing it with a cultivar that has an upright habit.
Burr! Turn Up the Heat
Crepe myrtles are not especially cold hardy. Some hybrids, however, like “Cherry Dazzle” or “Razzle Dazzle Cherry” (Lagerstroemia indica “Gamad I,” “Cherry Dazzle” or “Razzle Dazzle Cherry”) are hardy in USDA zones 6 to 10. Cold damage, usually to the uppermost branches, is common in USDA zones 5 and 6, even on “Cherry Dazzle.” The damage can be caused by unusually low temperatures, but also can be the result of a mild winter with a sudden spring temperature drop below 30 degrees Fahrenheit. This also can occur in early fall if the temperature drops suddenly.
The Damage is Done
Unusually cold temperatures cause the cells within crepe myrtle stems to freeze and form ice crystals within the wood beneath the bark. The ice crystals expand and cause the cells to rupture. It works in much the same way as popping a water balloon with a pin. When temperatures warm back up and the crepe myrtle begins to grow again in the spring, the damaged branches hang down due to the structural damage.
Cut It Out!
Fortunately, the damaged crepe myrtle stems can be pruned off and the tree or shrub will grow new, fresh, nonweeping stems. Crepe myrtles will bounce back even if all of the stems are cut down to a height of 8 inches in the spring, which is the way they are grown commonly in USDA zone 6. Alternatively, the damaged stems can be pruned back to healthy wood with loppers or pruners in the spring after the last expected hard frost. Make the cut just above a healthy, outward-facing growth bud. Wash and disinfect the loppers and pruners with household disinfectant before and after using them to prevent the spread of disease. Give the tree or shrub ½ to 1 cup of a balanced 10-10-10 or 8-8-8 fertilizer in the spring. Do not give it more than 1 tablespoon of fertilizer per foot of tree or shrub height. Spread a 2- to 3-inch depth of mulch over the root zone to insulate the roots. Prevent future damage by covering the crepe myrtle with burlap, an old sheet or newspapers when an unusual cold snap is predicted. Let the covering hang down to the ground to trap the heat.
- Floridata: Lagerstroemia Indica
- University of Florida: IFAS Extension: EDIS: Lagerstroemia x “Osage” Osage Crape Myrtle1
- Arizona State University: Chris A. Martin -- Plants -- Lagerstroemia Indica
- Missouri Botanical Garden: Lagerstroemia Indica “Gamad I” Razzle Dazzle Cherry
- Missouri Botanical Garden: Frost Injury and Ice Damage
- North Carolina State University: A Gardener’s Guide to Fertilizing Trees and Shrubs