"Collard Greens" refers both to the plant and the cooked recipe.
The collard plant is a large, loose-leafed dark green member of the cabbage family which grows easily and readily. It is unique because it flourishes in cool weather, often tolerating temperatures as low as 5°F (-10°C) if it is gradually acclimated, while a sudden cool snap will kill it. The plant may reach three feet tall by four feet wide. Though it is infrequently done, they may be cooked with any other loose-leafed greens (kale, turnip greens, spinach and mustard greens). Collards and other green leafy vegetables comprise several traditional "soul food" dishes of the southern US.
Collards are available year-round, but the best growing, and traditional, seasons are autumn or winter. Many people prefer their taste after the first frost, and believe them richer and more nutritious. Collards do become sweeter after the first frost, when photosynthesis is slowed.
When buying collards, make sure to choose dark green leaves with no wilting or yellowness. They may ideally be stored in the refrigerator about a week, but once they are cooked can be frozen indefinitely or added to other dishes as desired.
Collard greens belong to the family Brassica oleracea, which contains several varieties of cultivars including broccoli, cabbage, Brussels sprouts, cauliflower, Chinese broccoli, kale, and kohlrabi.
Traditional Southern recipes for collards often include some type of pork, sometimes a portion of the neck bone, which is boiled along with the greens.
Nutritionally, collards are an excellent source of calcium and vitamins A & C. They are virtually fat-free, low in calories and sodium, and are an excellent source of carbohydrates and dietary fiber. A one-cup serving of boiled collards contains 17 calories, 0.1g fat, 10mg sodium, 0.9g protein, 3.9g carbohydrate, 1.3g dietary fiber, 174.7 RE of vitamin A (17% US RDA), and 7.7mg vitamin C (13% US RDA).