Crape myrtle trees should be planted in full sun in soils with a pH of between 5.0 and 6.5 and given plenty of water at planting and during the first two years. If needed, give a light application of fertilizer, usually 5-10-5, in the spring. In areas with cold winters, stop watering in autumn to allow the tree's tissues to toughen up. The climate, along with available growing space, also determines when and how to prune the tree.
Pruning helps to control the size and shape of the crape myrtle. Some varieties, such as the Biloxi, may grow up to 25 feet tall. The Chickasaw is a miniature variety, only growing into a small shrub roughly three feet high. Regardless of variety, do minor pruning by removing lower branches or suckers from the tree's base. Trees not pruned in a while should have the dead branches removed and the living branches trimmed to encourage new growth and more flowers.
In warmer climates, pruning may usually be done year-round without harm. In places with snowy winters, it's best to avoid excessive pruning in the fall. The trees go dormant in the winter and the extra foliage provides some insulation. Miniature crape myrtles are a good choice for colder climates because they are easy to protect with tarps or commercial covers during the winter season.