Brussels Sprouts

Brussels sprouts are cool-season plants grown for the small buds that form along a thick stalk. They belong to the cabbage family, and they are among the cole crops, which are cultivated forms of the species Brassica oleracea. The plants usually reach 2 to 4 feet (61 to 122 cm) tall and wide. The sprouts look like little cabbages and measure about 1 to 3 inches across.

The plants grow best in cool weather, between 60 and 70 °F (16 and 21 °C). Cool weather during maturity is also what gives the sprouts good flavor.

Sowing indoors. Sow 2 to 3 seeds per cell about ¼ inch (6 mm) deep, and transplant the seedlings when they are ready at 4 to 6 weeks old. Start seed indoors 4 to 5 weeks before planting outdoors, as one Iowa guide describes for central Iowa, where transplants go out in early to mid-May.

Sowing outdoors. You can also sow directly in the garden about 4 months before the expected fall frost. Place 3 seeds every 18 inches (46 cm) at ¼ to ½ inch (0.6 to 1.3 cm) deep, then thin to one plant per spot. Many gardeners aim for a fall harvest, because the sprouts mature in cool weather.

Timing. Advice for gardeners in the Bay Area suggests setting transplants out in early August for short-season varieties of about 90 days, and earlier still for long-season varieties that can take up to 150 days.

Spacing and site. Space plants 18 to 24 inches (46 to 61 cm) apart in the row, with rows 30 to 36 inches (76 to 91 cm) apart. Give them at least 6 hours of direct sun each day, and ideally 8 to 10 hours. Choose a fertile, moist, well-drained soil with a pH between 6 and 7.

Watering. Brussels sprouts have shallow roots. If rain does not supply about 1 inch (2.5 cm) of water per week, they need weekly irrigation, and soaker hoses or drip lines are a good choice. Keep them well watered through the summer heat, since they need ample soil moisture.

Mulch and weeds. A 2 to 3 inch (5 to 8 cm) layer of mulch, such as straw or shredded leaves, helps control weeds and conserves soil moisture.

Feeding. Brussels sprouts need a lot of nutrients. Side-dress them 2 to 4 weeks after planting, or when the plants are 12 inches (30 cm) high. Get a soil test before planting and feed according to the results.

Topping. When the lower sprouts are ½ to ¾ inch (1.3 to 1.9 cm) across, remove the growing tip of the plant so the upper sprouts develop more evenly.

Cabbageworms, caterpillars, slugs, flea beetles and aphids can all feed on the plants. Leaf spots, black rot and blackleg are the listed diseases.

Cabbageworms are greenish caterpillars that chew large, irregular holes in the leaves. Treat them when first noticed with Bacillus thuringiensis (Bt). Flea beetles make small, round holes, and minor damage usually has little effect on yield.

Aphids are most likely in late fall or spring, when daytime temperatures are 65 to 80 °F (18 to 27 °C). Check the plants at least twice a week and knock or hose the aphids off. A forceful spray of water can help control them.

Plants that mature in hot, dry conditions may taste bitter or fail to form compact sprouts. An experienced Bay Area advisor reports that an unusual warm spell in winter can make the sprouts open early.

Harvest when the sprouts are firm, compact, deep green and about 1 to 1½ inches (2.5 to 3.8 cm) across. Start with the lowest sprouts and twist or snap them off the stalk. One or more light frosts improve the flavor, so waiting for frosty weather is worth it. Harvest before the leaves turn yellow.

Opinions differ on the lower leaves. One guide says they can be removed to speed sprout development, while another says to leave them on, because they are needed for further growth.

For the best flavor, refrigerate sprouts for no more than a day or two, although they can keep 3 to 5 weeks. Placing them in a perforated plastic bag in the refrigerator also keeps them for 3 to 5 weeks. Blanched and frozen sprouts keep for up to one year.