Grown as cool season annuals, both kale (Brassica oleracea var. viridis) and broccoli (Brassica oleracea var. botrytis) belong to the cabbage family. The edible plant parts are the immature flower heads for broccoli and the leaves for kale. Kale has the greatest cold tolerance, with some varieties harvested even underneath snow. Both are rich in vitamins and minerals, but broccoli has more protein than kale.
Kale is more tolerant of varying weather conditions than broccoli. Kale tolerates cold temperatures, improving in sweetness when exposed to several nights of 20 degrees Fahrenheit. Siberian kale (Brassica napus) varieties "White Russian" and "Winterbor" can withstand temperatures to 15 degrees F. Kale bolts during hot weather, but the variety "Rainbow Laciniato" is the slowest to bolt. Broccoli is sensitive to temperature extremes. If subjected to prolonged exposure to nights around 30 degrees F and days of around 50 or 60 degrees F, broccoli produces immature heads. Unexpected warm periods causes flower heads to open up too soon, called ricing.
Plant both crops in either spring or fall. In cold winter climates, set out kale transplants three to five weeks before the last frost and again in late summer six to eight weeks before the first predicted frost date. In mild winter climates of U.S. Department of Agriculture plant hardiness zones 8 through 10, plant successively throughout the fall for winter and spring harvest. Plants won't grow in hot summer climates. Broccoli grows best with daytime temperatures between 70 and 80 degrees F. For cold winter areas, plant broccoli in spring and again in late summer. In mild winter areas, plant broccoli in the late fall.
Kale is essentially a primitive, unheaded cabbage. Leaves form sequentially on a central stalk. Harvest the lower leaves first, leaving a minimum of four leaves at the top of the stalk. In USDA zones 7 through 10, kale will keep producing new leaves all through the winter. Kale is more space-efficient, since you essentially use the whole plant. Broccoli plants take up a lot of space and you only harvest a small portion of the plant. When the flowering heads form but are still tight green buds with no yellow showing, cut the central head off with 6 inches or less of stem below the head. The broccoli will form new side branches of small, 1- to 2-inch heads. Harvest the heads frequently, because if flowers start to open, the plant stops growing.
Kale has abundant supplies of vitamin K, the B-vitamin folic acid, beta-carotenes needed for manufacture of vitamin A and other antioxidant carotenoids such as zeaxanthin and lutein. It also has calcium along with the magnesium needed to properly assimilate calcium into the body. In addition, per each 12.6 ounce portion of cooked kale, there are 7.2 grams of carbohydrate, 7.2 grams of fiber, 3.2 mg of iron and 6.8 grams of protein. A similar portion of broccoli has more protein, folate and fiber, but less calcium, magnesium, potassium, vitamin A and vitamin K. How you prepare broccoli can enhance its nutritional value. Cutting broccoli into small pieces and adding lemon juice before cooking is helpful. Light cooking aids digestibility by softening fiber and making nutrients easier to absorb. Broccoli should be boiled or steamed for three to five minutes.
- Winter Harvest Cookbook; Lane Morgan
- Ohio State University Department of Horticulture and Crop Science: Seed ID Workshop -- Brassica Oleracea Var. Botrytis -- Broccoli
- Dr. Fuhrman: FAQ -- Protein Content of Green Vegetables Compared to Meat?
- Mother Earth News: The Best Kales
- Ohio State University Department of Horticulture and Crop Science: Seed ID Workshop -- Brassica Oleracea Var. Viridis -- Kale; Collard; Ornamental Kale
- Organic Gardening: Learn & Grow: Broccoli -- A Growing Guide
- Gardens on the Go - Organic Horticulture: Growing Kale
- Bonnie Plants: Growing Kale
- Mother Earth News: All About Growing Broccoli
- Mother Earth News: The Best Tasting Broccoli Varieties to Grow in Your Garden
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