Other cultural tips - plant your crepe myrtle in full sun in slightly acid soil. A heavy soil that retains moisture is fine, but waterlogged spots are not. A weekly deep watering during dry spells is beneficial. Crepe myrtles don't need a lot of fertilizer, which encourages vegetative growth at the expense of flowers. One application of a balanced fertilizer when spring growth kicks in is all that's needed for an established crepe myrtle.
Some folks grow small forms a zone or two further north as die-back perennials.
Check with a local arboretum or extension service for a cold-hardy type that's likely to succeed in your area.