planting around an existing tree

by Samantha
(Texas)

I have an existing oak tree that has multiple roots showing above the ground. We put in an asphalt driveway, but left an approximate 5 ft. circle around the tree. Then we put a rock border at the edge of the asphalt. We would like to put in a flower bed around the tree, but are concerned about whether this would kill the tree. I have read that if you use good soil (not a clay) and don't go up the tree trunk, that the tree would do OK. Can you help me?