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How to Grow: Broccoli
Whether it’s sprouts or large heads, this Italian delicacy has become increasingly popular over the last 20 years, showing up in salad bars, casseroles, soups, and steamed side dishes. Broccoli (Brassica oleracea) is loaded with vitamins A and C and contains the antioxidant sulforaphane, which is a known cancer fighter.
In my Italian family, we love the broccoli relatives, such as broccoli raab or gai laan, where you eat the whole plant. They have small flower heads and tender stems and leaves.
When to Plant
Broccoli grows and matures best in cool weather. Sow seeds or plant transplants from late April to late May for an early summer crop, and again from late July to August for a fall crop. Direct sow seeds in the garden 2 weeks before the last expected spring frost date, or start transplants indoors 4 weeks before you intend to plant them outside. Although broccoli is frost tolerant, if it’s grown for several weeks with temperatures below 50 degrees F, it will flower prematurely and form small heads. Conversely, if they’re maturing during hot weather, the flower heads will also be small.
Where to Plant
Broccoli grows best in full sun in fertile, well-drained soil. Broccoli is a heavy feeder, so amend the soil generously with compost before planting. Consider planting quick maturing crops of mesclun mix and radishes around broccoli plants since broccoli will take up to 60 days to mature. These veggies will mature before the broccoli plants get large enough to shade them out and you’ll get a quick crop of greens from otherwise wasted space.
How to Plant
Broccoli germinates and grows quickly from seed. Sow seeds 6 inches apart in rows spaced 36 inches apart. Thin the seedlings to 18 inches apart once they have 4 leaves. Plant purchased or started seedlings 18 inches apart. Smaller headed varieties may be spaced closer together to save some room—perfect if you have a small, urban lot.
Care and Maintenance
Weed the broccoli patch well once plants are established, and then mulch with an organic material such as untreated grass clippings or straw. To get the largest heads, side dress your broccoli crop with a balanced organic fertilizer, such as 5-5-5, 3 weeks after transplanting.
Protect young seedlings from cutworms by wrapping a 3-inch-thick strip of newspaper around the stem, keeping it 2 inches above the ground and 1 inch below. Spray plants with Neem oil to control flea beetles. If you want to avoid the notorious floating green worms when you cook your broccoli (my wife hates these), check leaves and heads for signs of the green cabbageworms and cabbage looper insects. They’re easy to control with sprays of Bacillus thuriengensis (Bt).
Once the broccoli heads form, but before the flower buds open, cut the heads off the stem about 6 inches below the head. Most varieties mature about 60 days after transplanting. Head size can range from 3 to 9 inches in diameter depending on the variety. It’s important to harvest broccoli before the flowers open or the flavor will be bitter. The exceptions are broccoli raab and gailon; these can be allowed to flower and still taste good.
Most broccoli varieties will form side shoots off the main stem after the head is harvested. Continue harvesting these shoots as they form by cutting the entire side shoot back to the main trunk. This side shoot formation can continue into fall as long as the plant stays healthy.
‘Arcadia’, ‘Bellstar’, and ‘Marathon’ are widely adapted hybrid varieties with good disease resistance. ‘Bellstar’ is especially adapted to spring and summer growing, while ‘Marathon’ does especially well in fall. ‘DeCicco’ is an Italian heirloom with small, flavorful heads and prolific side shoots.
‘Santee’ is a new hybrid sprouting variety that features small purple heads and abundant side shoots. It’s best grown as a spring or fall harvest. The purple color turns green when cooked!
Text excepted from the Northeast Vegetable and Fruit Gardening book.