Collards grow 2 to 4 feet tall and have tufted rosettes of leaves growing on sturdy stems. They are a member of the cabbage family, although they do not form a head. Best grown in the spring or fall as the heat of summer often causes the leaves to grow bitter. Steamed collards are an excellent source of vitamin A, mostly in the form of beta-carotine as well are loaded with vitamin C, calcium and fiber.