Perhaps the history of the plant might help (I notice the Physostegia next to it is still blooming, I thought they had finished here but I will check). Was it purchased this year in a pot, or was it divided from someone's clump, maybe it had been cut back earlier for some reason which could delay flowering? Or has it been growing in that spot for more than a season undisturbed? The established Persicaria polymorpha here is at the reddish transitioning to brown stage, but some that I had to move are still flowering white. The latter are still more advanced than the picture above though.
Is your 5a zone on the Canadian zone system or USDA?
