Kale, or leaf cabbage, belongs to a group of cabbage (Brassica oleracea) cultivars grown for their edible leaves, although some are used as ornamentals. Kale plants have green or purple leaves, and the central leaves do not form a head (as with headed cabbage). Kales are considered to be closer to wild cabbage than most of the many domesticated forms of Brassica oleracea.
There are many kale varieties, and they're all worth a try. The curly-leaf varieties tend to hang on longer in cold weather. But the flat-leaf types generally become established faster.
Kale has a relatively fast growth rate and can grow from seed to harvest in about two months. It is a biennial plant that typically is grown as an annual. It is best direct sown or transplanted in the late winter/early spring in cooler climates, and late summer in warmer climates, for fall-winter harvesting.
Kale is usually an annual plant grown from seed with a wide range of germination temperatures. It is hardy and thrives in wintertime, and can survive in temperatures as low as –15.0° Celsius. Kale can become sweeter in taste after a heavy frost.
Water your kale plants regularly so the soil stays evenly moist. Along with cool temperatures, moist soil helps to keep the kale leaves sweet and crisp, rather than tough and bitter. Mulching around your plants can help to keep the soil cool and to retain moisture.