I picture a roadside garden as likely being hot and full sun, and you mentioned the low water requirement (drought resistant). I wonder if the oak leaf hydrangea would be a good choice for those conditions. I think they are pretty flexible, but I don't know if they are that flexible. If you give more site specifics, maybe someone can give recommendations.

This area has a rock cliff and a few trees on one side,so areas of sun and part sun and shade. Any water will come from the sky or hauled in. My experience with oakleaf hydrangea is that it is more drought tolerant than other hydrangeas. Thanks for any input. I got some plants at the swap that will be in this garden. Thanks everyone!