Leslie Renee, Linda Beck, Song of the Empire and Stenciled Impressions have all been here quite a few years. They've overwintered without any trouble or special treatment in my zone 4 garden. Temps can get - 30 to - 40, normally with snow cover but a few years ago we had an open winter with no snow. They still did fine.
Levi Davis is another one in the garden, it does struggle a bit in the spring to come up but catches up quickly and blooms.
