Answer: This plant will die back to the ground during excessively cold winter weather, so that would be normal. It would in fact be considered only marginally hardy in your area, so use a heavy mulch each winter to give it the best chance of survival. Each spring, trim away the dead wood. This plant blooms on new growth of the season, so trimming it in late winter or early spring is not a problem. You might trim it back a bit in fall to reduce the wind blowing it around during the winter, but leave the bulk of the plant in place until spring to provide just that little bit of extra protection. For the best regrowth, it likes a rich soil, ample water, and full sun. In a shorter growing season it may not reach its full potential size, and in colder climates it may not always survive the winter, but many gardeners like it so much they grow it anyway.
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