I know a lot of people are not going to be happy about the next thing I'm going to say, but I gotta say it anyway. Crape Myrtles are not native trees. It's taken me way too long to appreciate the importance of 'going native'.
I agree that Crape Myrtles are very pretty. But trees/shrubs/plants/grasses that are native to your neck of the woods are going to thrive. They will require less of everything -- less water, less or no fertilizer, etc. Why? Because it's where they want to be. And less work sounds good to me.
One other plus for going native is that the birds and butterflies will thank you.
