Trees and shrubs are best planted in the fall. You can plant them now, but be sure to water them in Sept and Oct if we don't get adequate rain. Once November arrives, nature should take care of the job.

Here's a link to a planting guide that may be of some help. Please email me with any questions or if you see anything about the instructions that could be improved.

Here is a link that might be useful: Planting a Tree or Shrub

Brandon, thanks for linking to a page that states to fill the hole with native soil. I have been working with a professional tree outfit, and they are also beginning to utilize this strategy when in the past, they have not, necessarily.
It is important to choose the site carefully, the right tree for the right spot - instead of trying to force the wrong spot on that poor tree!

Honestly, I don't think Crepe Myrtles care. They're weeds in our climate. That is, like a Holly, it is almost impossible to kill one once you put it in the ground, and you can prune them to the ground after 2-3 months and they'll grow back from the base.