Cabbage is a brassica crop — related to broccoli, cauliflower, kale and Brussels sprouts — that thrives in cold. Because of its frost tolerance, cabbage is perfect for starting your gardening season early in spring or for extending it into the fall. Cabbage isn’t just a cool-season crop — it’s a cold-season crop. It can tolerate frosts as cold as 20 degrees Fahrenheit. On the other hand, in hot weather, cabbage will “bolt” which means it will send up a flower stalk before the plant is ready to harvest. A bolted cabbage will turn bitter and won’t form the head that gardeners desire. To avoid bolting, cabbage planting should be timed for a spring crop or a fall crop. Note that fall-grown cabbage that matures in cool weather will be sweeter than spring-grown cabbage and far less likely to bolt.