Greetings, Although I cannot speak to a climate with recurrent frosts all winter long, I can say that Giant Coreopsis can handle frost. Here in the flatlands of Berkeley, we had 5 or so frosty nights and mornings here just after Thanksgiving. Frost was forming by 10PM the nights before and by morning all my plants, including 2 Coreopsis, were crystalized with frost. The frost did not linger past 10am or so. Both of these plants were in new growth with 2-6" of foliage. The plants are 8" and 12" tall with 2" diameter stems. Given their habitat, I would doubt they can handle a hard freeze - but they handle frost just fine. -Kipp McMichael Berkeley, CA USDA Zone 9