Photo showing a patch of lush dark green / purple curly kale plants, growing in an allotment vegetable garden in the autumn. Kale (borecole) is a particularly hardy variety of brassica (Latin name: brassica oleracea) and happily tolerates harsh cold weather. Closely related to wild cabbage, curly kale is known for its dark green, tightly curled leaves, which attract water droplets / morning dew drops. The leaves are best picked when they are young and at their most tender.