Although crape myrtles are fairly drought tolerant, they perform best in moist soil. Make sure newly transplanted plants are watered often, either by the rain or a sprinkler or drip system. Once they are established and rainfall is normal, they will not need supplemental watering. During periods of drought, if local water restrictions permit, run the sprinkler or drip system on crape myrtles and other trees and shrubs for 20 to 30 minutes every week or so. Try to soak the soil down about 10 or 12 inches. A layer of mulch on the soil under the shrub or tree will help keep the soil moist by controlling evaporation and runoff. (See below).
For more information see file on About Fertilizers.
Crape myrtles respond to fertilization. Since many types are fairly fast growers and they produce copious blooms they benefit from extra nutrition. In the spring sprinkle a granular, all-purpose fertilizer formulated for acid loving plants on the soil under the shrub or tree out as far as the branches reach for the rain or sprinkler to water in. Consult the package label for specific amounts, but a rule of thumb is 1/2 pound per 1/2 inch of trunk diameter for trees. Do not allow the fertilizer to fall on the stems or foliage. Since crape myrtles bloom heavily late in the growing season, a light sprinkling of this same fertilizer or a spray of dilute liquid fertilizer on the foliage in early August, no later, will give the shrub or tree a boost. Do not overdo, as crape myrtles normally grow vigorously and densely without any encouragement.
For more information see file on About Watering Equipment.
A 2 to 3 inch layer of some attractive organic material spread on the soil over the crape myrtle root system has many benefits. A layer of wood chips, pine needles, chopped leaves, pine needles or shredded bark will discourage weeds, help keep the soil moist and provide a barrier against injury to the tree or shrub from mechanical yard care equipment.
For more information see file on Using Mulch.
Crape myrtles may be pruned for health or control purposes. All types of this plant may need to have diseased or damaged stems cut out from time to time. This should be done promptly, regardless of the time of year. Some homeowners prune back larger tree-like varieties of crape myrtles in the early spring to control their height. They cut the stems back nearly to the ground which forces the plant to produce larger flowers on fewer stems and remain about 4 or 5 feet tall. It is obviously not necessary to do this on the newer, shrubier versions of crape myrtle. Those planted for hedges will need some grooming each season. Always do any cosmetic pruning in the early spring before new growth starts. Otherwise the wood on which this season's flowers will bloom is removed.
For more information see files on Pruning Shrubs and Hedges and Choosing Pruning Tools.
In the northern reaches of its range, crape myrtle will benefit from some winter protection. Water the tree generously before the ground freezes and increase the mulch layer to 4 inches to insulate the ground somewhat from fluctuating temperatures over the winter. In these colder areas, expect that the tops of crape myrtle shrubs/trees may be frosted and die and plan to prune them in early spring. In some instances the entire plant may die back, emerging as new shoots in the spring like a typical perennial plant.
For more information see file on Winter Protection For Plants.