Winterbor kale is a Dutch hybrid variety of kale with thick, blue-green leaves that is very frost hardy. It can grow up to 3 feet high and 2 feet wide. The flavor of Winterbor kale intensifies with frost, and it has a sweet, mild tang. 
Winterbor kale can be sown in early spring for summer harvest, or in mid-summer for fall and winter harvest. The leaves can be chopped and used raw in salads, or added to soups or stir-fries.