Rutabagas are a cross between cabbage and turnips. They are sweeter than turnips with a lower water content. While similar in shape and size to turnips, rutabagas are high in vitamin A and low in calories, sodium, fat, and cholesterol. Rutabagas are often mashed, used in casseroles, or eaten with cheese sauce. They are planted in spring and harvested in late summer or early fall, storing well in cold, dark places for months. Rutabagas are often purchased from farmers markets in early fall when their flavor is at its peak.