Crape Myrtle

We have the world's most anemic crape myrtles. Two of them. Side by side at the end of our driveway. We bought them years ago on the way home from the beach (they were just some tiny ones that some woman at a flea market had potted up). Every other crape myrtle I see in town has been gloriously in bloom for weeks. Ours... not so much. It's the same every year. Is it the plant itself, or our soil? Or the tree right behind them? Who knows!