Over the centuries, selective breeding of wild brassica species to emphasize leaves, flowers, or roots has led to the wide variety of these sturdy, nutritious vegetables. There’s been a boom in brassicas, especially broccoli, in the past couple of decades, after researchers reported possible links between diets high in cruciferous vegetables and lower risks of some kinds of cancer. This possible health connection may be due to sulfur-containing compounds called glucosinolates. (The sulfurous compounds are also responsible for the unpopular aroma of overcooked cabbage or Brussels sprouts.) More recent research has tempered some of the earlier enthusiasm, however, and scientists now say that further work is needed to demonstrate whether or not brassicas play a role in preventing cancer. But there remains no doubt that cruciferous vegetables, especially broccoli, are rich sources of vitamin C, folate, carotenoids, and other beneficial compounds, as well as abundant fiber, known to deter colon cancer.
The bad news is that the benefits are greatest if cole crops are eaten raw. Cooking breaks down the beneficial compounds and dissipates the vitamins. Slaw, anyone? Or broccoli sprouts? If you can’t choke down raw broccoli, the best alternative is to cook these vegetables as little and as lightly as possible—a quick steam, stir-fry, or sauté rather than a slow stew.
Brassicas are known for their cold tolerance. Traditionally in the South, collard greens grow all winter on tall stalks and are harvested a few leaves at a time, says Powell Smith, an educator with the Clemson University Extension in Lexington, South Carolina. But in most of North America, brassicas are spring and fall crops. Wherever they’re grown, cabbage and its relatives don’t do well in hot, dry weather.
Brassicas can be seeded where they are to grow in the garden, but more often they are started indoors or in a greenhouse and transplanted to the garden as seedlings. Spring crops can be tricky; it’s important to get the timing right so the crops are harvested before hot summer weather that tends to make them bolt. Up north and in the Great Plains, look for early varieties—those with the fewest days to maturity. Gardeners can save several weeks of growing time by purchasing transplants of broccoli, cabbage, and other brassicas at garden centers in spring.
As fall crops, brassicas often are started indoors in early summer and transplanted to the garden in July or early August, when there will be 90 to 100 days before the first frost. To withstand the summer heat, the tender transplants benefit from a little shade from nearby vegetables or floating row covers and careful watering as they become established. In fact, all brassicas need a steady supply of water. Soaker hoses or drip irrigation is a good idea, at least until autumn rains come. An organic mulch over the root zone will hold in moisture, reduce weed competition, and insulate soil against temperature extremes.
Brassicas need a soil pH between 6.5 and 7.0 to reduce the risk of club root, a fungal disease associated with acid soils. It’s always best to get a soil test before starting a vegetable garden, to determine not only your soil’s acidity but also its nutrient level. Like most vegetables, brassicas thrive in well-drained soil with lots of organic matter. They need ample nitrogen, so soil should be enriched with plenty of mature compost. A nitrogen-fixing cover crop such as clover helps increase soil fertility, or simply plant brassicas where you’ve recently harvested beans. It’s important to rotate crops anyway, since these plants are subject to a number of soilborne diseases. Four to six weeks after the plants are set out in the garden, side-dress with more compost, or apply seaweed emulsion or other organic fertilizer in moderation. Midseason applications of fertilizer are especially helpful in nutrient-lean sandy soil.
Among insect pests, cutworms—easily defeated by collars made from cut-down paper towel rolls—and flea beetles may plague new transplants. All pests of cabbage—cabbage loopers, cabbageworms, aphids, and maggots—will happily munch its vegetable cousins as well. Some farmers spray Bacillus thuringiensis (BT), a predatory bacterium, as a control for leaf-eating caterpillars. Cindy Tong, postharvest horticulturist with the University of Minnesota Extension, recommends using lightweight floating row covers all season long to deter flying insect pests from laying eggs.
Smith, who grows plenty of brassicas in his home garden, advises another pest-defeating strategy. He surrounds the vegetables with a diverse garden of nectar-bearing flowers to lure predatory insects and parasitic wasps to prey on the brassica pests.
Broccoli, the darling of nutritionists, loves steady, cool weather. That’s why most commercial production takes place along the central California coast, where Pacific Ocean fogs and breezes keep the fields cool enough to grow it year-round.
Although the entire broccoli plant is edible, we grow it mainly for its tightly packed clusters of green flower buds. Historically, broccoli plants had multiple long florets in a loose bunch. In recent decades, varieties bred for a single, large flower head have come to dominate in the United States, though older, looser types—called sprouting broccoli—are still popular in Europe. Many big-headed varieties will keep producing smaller side florets for weeks if left in the ground after the main head is harvested.
Broccoli is relatively sensitive to both summer heat and autumn frosts, so choose varieties and planting dates carefully. Days and nights must be cool for heads to form. For spring crops, set out transplants when they have two to four leaves about 2 weeks before you expect your last frost; for fall crops, set the transplants out in late July or early August.
A plant often called purple cauliflower is actually a long-season type of broccoli that can be planted in early spring for fall harvest or in fall to overwinter for spring harvest in USDA Plant Hardiness Zones 6, 7, and 8. If it is harvested before frost, it tastes more like broccoli; if harvested after frost, it evokes cauliflower. Sadly, it loses its purple tint when cooked.
Romanesco broccoli, also called Romanesco cauliflower or broccoflower, has a lime green, alien-looking flower head with a swirl of pointy protuberances. It requires lots of space and a long growing season but has an interesting nutty flavor when cooked. And broccoli raab? Different species.
Recommended Broccoli Varieties
Chinese broccoli is known across Asia by a variety of names, including kailaan, gai lan, and kai-lan. Rumored to be descended from cabbage plants brought to Asia by Portuguese sailors, it is grown for broad leaves, crisp stalks, and small florets somewhat like those of sprouting broccoli, with a similar but slightly more bitter taste. It’s widely used in Asian cooking; in America, Chinese broccoli is most often stir-fried.
Chinese broccoli is grown much like broccoli. But you can harvest the leaves and stems young and tender, before the flowers develop, which makes it a handy crop in short-spring climates. You might have time to direct-sow seeds in the spring garden and do the same in late summer for fall greens.
Recommended Chinese Broccoli Varieties
Cabbage is an ancient and diverse crop closely related to kale and collards. Today’s supermarket varieties have round, heavy heads of pale, tightly wrapped leaves. But you also can grow savoy cabbage with crinkled leaves, red cabbage, and head cabbage var-ieties that lie open like roses or stand tall like pinecones. Cabbages need elbow room—it’s nothing for a plant to be 3 feet across—so plan space carefully in the garden.
In the South, cabbages are planted in fall and can be left in the garden over most mild winters. In northerly climates, they can be planted both in spring and fall. Some gardeners plant two fall crops—an early one for eating and a late crop for keeping.
For spring harvest, start cabbage seeds indoors in late January or February and set the plants out in the garden about a month before the expected last frost. For the fall crop, sow seeds indoors or direct-sow them in the garden in July.
Recommended Cabbage Varieties
In smaller gardens, Brussels sprouts fit right in: They grow more up than out. The actual sprouts, like tiny cabbages, grow along a tall stalk under leaves that spread like a palm tree’s. Brussels sprouts are said to have developed from a chance mutation of a cabbage plant in Belgium in the 18th century.
Brussels sprouts are slow-growing and hate hot weather, so they are tricky to grow in the South. Even in the North, they are best as a fall crop. Start the seeds indoors early enough to transplant them 90 to 110 days before the first frost.
Sprouts will start forming at the base of the stalk when nights are routinely down to 60°F; harvest them as they mature. Brussels sprouts are the most cold-tolerant of brassicas, so you can leave the plants to keep producing well into fall, sometimes after snowfall. The top is edible too; cook the leaves as you would kale.
Recommended Brussels Sprouts Varieties