Kale contains the highest levels of beta-carotene of any green vegetable, is high in vitamin C and has lots of calcium. Collards are not far behind. All are easy to grow, vigorous, nutritious, resistant to cold, easy to harvest and prepare. Kale seeds are very easy to grow and are winter hardy, making it an ideal vegetable for the winter-harvest garden. Kale even get sweeter after frost. Choose from over 12 hardy varieties.