I love these trees! We have two that are growing out front near our mailbox. They have been there a long time. Last year we bought 2 from Home Depot. This picture is of one of them. They bloom most of July and August. Beautiful! Below is some information I found about them.
Crape Myrtles are different from most other trees and many other shrubs in that they bloom on what's called "New Wood or New Growth"(most tree's flowers come from the growth they made the previous year).
Therefore, anything that you can do to make the crape myrtle grow once it leafs out in the spring will result in more flowers this coming year. Crape Myrtles thrive on water and fertilizer and if you fertilize once a week or every 2 weeks you will have more flowers for a longer time than you know what to do with.