Japanese anemones ?
Years ago, I had gone on a quest to find Japanese anemones that flower early enough to give a good decent display before frost. I had grown many varieties, most only opening their first buds with hard frost upon us ... though, 'Serenade' has generally begun flowering in mid August and in most seasons providing a most satisfactory result. Placement on the sunny south side of the house, planting deeply and providing winter protection has proven successful, though it has also come through two winters in the open garden without any fussing, though that just might be a fluke. This spring, I had dug the plant to amend the soil, unfortunately neglecting to quickly get it back in the ground and the thing had dried and fried up ... oh, that precious anemone, lol. I then thought best to pot it up and give it some TLC, though it sulked and looked pathetic and appeared as if it might perish, never mind even flowering this summer. Later, had given the struggling plant some doses of fertilizer that kicked it into high gear and 'Serenade' has now produced more blooms than I could have imagined. I'll now probably maintain both a potted and in ground specimen.
Anemone tomentosa 'Robustissima' is said to be one of the hardiest and earliest flowering, I'll have to give that one another try, I had it back on the farm, though it had quickly died in the hard dry soil there.