The most widely grown kale in the United States, was developed in 1950 from the heirloom variety “Dwarf Green Curled,” that helped set edible kale standards (green, frilly, upright leaves) since before 1865. As with all kales, a frost improves sweetness. This type is known to be especially hardy and tough but it will overwinter with plenty of mulch, even in the North. 50-80 Days.