Very pretty plant I wish I could keep it , maybe I will try again too (if I can find it ) and keep it in the greenhouse overwinter.
My greenhouse is not heated , but I have figured most perennials I loose have to do with the wetness of our winters.
I have found the same thing here Cinda. Except I killed my 'Druett's Variegated' by not watering it over the long winter. It was under the deck roof so got no rain. It dried up like crispy critters.