Broccoli

Broccoli is a cool-season vegetable grown for its compact clusters of unopened flower buds and the thick stem beneath them. It belongs to the cabbage family, Brassicaceae. The green-headed type is also sold as Calabrese. Plants can grow about 1 to 4 feet (30 to 122 cm) tall, and two crops a year, spring and fall, may be grown in many parts of the country.

Broccoli can be started from seed or from transplants, so plan the timing around your last spring frost. Seeds go in about ¼ to ½ inch (0.6 to 1.3 cm) deep. Gardening experts advise sowing seed 2 to 3 weeks before the last spring frost. Gardening experts suggest starting seed indoors 4 to 5 weeks before planting outdoors and setting out young, stocky transplants. Maryland starts seed indoors for early spring transplants and direct sows for fall, and direct seeding is possible, especially for a fall crop. Plant in fertile, well-drained soil rich in organic matter.

Spacing. Guides differ on final spacing. Gardening experts suggest 12 to 18 inches (30 to 46 cm) apart in rows 2 to 3 feet apart. Gardening experts suggest 18 to 24 inches (46 to 61 cm) apart in rows 24 to 30 inches apart. Maryland gives 16 to 24 inches (41 to 61 cm) apart in the row. Thin seedlings when the plants have 3 to 4 true leaves.

Timing and temperature. Maryland sets out five- to seven-week-old transplants about four weeks before the last spring frost. Temperatures below 45 °F (7 °C) may stop heading or trigger seed stalks.

Water. Keep the root zone moist with deep, regular watering, and water more often once heads start to form. Gardening experts estimate about 1 to 2 inches (2.5 to 5 cm) of water per week. Gardening experts recommend a 2 to 3 inch (5 to 8 cm) layer of mulch to control weeds and keep moisture in.

Soil and feeding. Gardening experts recommend a soil test first. Without one, it suggests 10-10-10 at 2.5 pounds per 100 square feet (1.1 kg per 9 square meters) before planting, then calcium nitrate side-dressing three to four weeks after transplanting. Soil pH advice differs: gardening experts give 5.8 to 6.5, while gardening experts give 6 to 7.

Bolting. Broccoli can bolt, producing a flower stalk, after 10 or more consecutive days between 35 and 50 °F (2 to 10 °C) following good growing conditions. Gardening experts suggest slow-bolting varieties such as Green Magic. Daytime heat of 86 °F (30 °C) or more can keep plants from forming heads.

Early tiny heads. Stressed plants, including large rootbound transplants, may form small heads early, called buttoning, which are not usable.

Hollow stem. Hollow stem is the most common problem in broccoli. Gardening experts say it can only be managed preventively, so a problem one season should be expected again the next.

Pests and disease. Cabbageworms, cabbage loopers and cabbage aphids can be a problem. Flea beetles can severely damage small seedlings. Black rot becomes a problem when moisture lasts for long periods and crop rotation is skipped. Maryland also lists Alternaria leaf spot.

Harvest before the flower buds open. Gardening experts suggest cutting when the main head is 3 to 6 inches (8 to 15 cm) across, about 6 inches (15 cm) below the head. Gardening experts describe heads about 6 to 7 inches (15 to 18 cm) across, while gardening experts give 6 to 12 inches (15 to 30 cm). Maryland gives 55 to 65 days from transplanting, longer for fall crops. Smaller side heads follow after the central head is cut.

Store unwashed in loose, perforated plastic bags in the refrigerator. Gardening experts say it keeps up to a week that way, and gardening experts and Maryland give 10 to 14 days. To freeze, blanch in steam for 6 minutes or in boiling water for 4 minutes, cool it, then freeze; it keeps up to one year at 0 °F (−18 °C) or below.

The stem, flower buds and flowers can be eaten. Gardening experts list broccoli under problems for horses, without naming the part of the plant or the amount involved.