Cabbage, Broccoli, Cauliflower, and Other Brassica Crops

Introduction

Brassica vegetables include the waxy-leaved crops cabbage, broccoli, cauliflower, Brussels sprouts, kale, and kohlrabi (all Brassica oleracea), as well as non-waxy Chinese cabbage (B. napa), mustards (B. juncea), and bok choi (B. rapa var. chinensis). These crops are also called "cole" or "cruciferous" crops. B. oleracea are of European origin and the others were domesticated in Asia. All are well-adapted to New England conditions. Plants that mature in cool weather conditions are of especially high quality. This diverse family has similar cultural requirements, diseases, and pests.

Types and Varieties

• Cabbage is the most widely grown and easily cultivated of the brassica crops. Varieties mature anywhere from 60 to 120 days or as many as 120 days from transplanting. The early and mid-season varieties are generally better suited for fresh market sales, 3-4 lb heads are desired. 
• Cauliflower is more difficult to grow than other brassica crops. Common problems include failure to head properly and poor curd quality. Fertile, moist soils with relatively high organic matter and nitrogen are required for successful cauliflower production. Conditions that reduce the vigor of the plant and slow vegetative growth, such as cold temperatures at transplanting encourage buttoning (premature, unmarketable heading). Cauliflower varieties range in maturity from 55 to 95 days.
• Broccoli is not as exacting in its requirements as cauliflower. However, it must be harvested promptly to avoid flowering. The earliest spring plantings often experience buttoning. In summer months, temperatures over 85° F during the critical period when the head begins to form can result in poor head quality. In southern New England, broccoli is best grown as a fall crop. Broccoli varieties range in maturity from 55 to 75 days.
• Brussels sprouts are a long-season crop grown for harvest in the fall. Brussels sprouts should be harvested when they are round, firm, tight, and of good color. Brussels sprout varieties range in maturity from 90 to 110 days or longer.
• Kale is cold-hardy and grows best as a fall crop when grown for full-size leaves, but can be succession-planted all season. Kale is also commonly grown for baby leaf as a component of salad mix (see Salad Mix section). The flavor of the leaves is improved after a light frost.
• Kohlrabi looks like a turnip growing on the top of the ground with leaves sprouting over the surface. Most varieties must be harvested when 3" in diameter, as they risk becoming tough at larger sizes but fall storage kohlrabi varieties can be grown to 6" in diameter. 
• Chinese cabbage, mustard, and bok choi are grown both as salad or braising greens and heading crops. See Salad Mix section for more details on production of salad mix. Crops in this group are more susceptible to damage from flea beetles compared to B. oleracea due to the lack of leaf waxiness, but tend to be less attractive to caterpillar pests. When grown as heading crops, these should be direct-seeded from early May to mid-July depending on intended harvest date and location in New England. Chinese cabbage is especially sensitive to bolting in response to stress or cold. Nitrogen management for Chinese cabbage should differ slightly from other brassica crops (see Soil Fertility below).

Most brassica greens, such as mizuna, mibuna, tatsoi, komatsuna, arugula, and mustard are direct-seeded. Some varieties are prone to bolting, which can be caused by cold temperatures in the spring or transplanting stress. Plant densities vary tremendously and should be geared toward the intended harvest age and size.

Brassica Crop Varieties

Soil Fertility

Apply lime according to soil test to maintain soil pH at 6.5-6.8. Maintain a high level of calcium to minimize tip burn.

Brassica crops are sensitive to boron (B) deficiency. The best method for applying a small amount of B is as an additive to the fertilizer. For example, if the level of B in the soil is low, apply 3 lb of B/A (15 lb Solubor or 30 lb Borax) before planting broccoli and cauliflower, and 2 lb/A for cabbage. See Tables 6 and 6a.

For Chinese cabbage, pepper spot can develop on the midribs as a result of excess nitrate uptake. Apply only 50 lb of nitrogen at planting and sidedress additional nitrogen at diminishing rates as the plant nears harvest maturity, for a total of 150 lb/A. Foliar or drip applications scheduled at 6-8 lb per week may be the most practical.

Less nitrogen fertilizer will be needed if legume sod was plowed down or if manure was applied (see Table 1 and Table 7).

If using transplants, use of a liquid starter fertilizer at planting time is beneficial, especially under cool soil conditions. Use a high phosphorus starter fertilizer mixed at a rate of 3 lb per 50 gallons of water. Apply 8 fluid ounces (1 cup) per transplant.

Plant Nutrition Recommendations According to Soil Test Results for Cabbage, Broccoli, Cauliflower, and Other Brassica Crops

Planting and Field Culture

Early plantings of brassica crops are generally made by setting out transplants grown in greenhouses or cold frames. Transplants should be 5-7 weeks old at field setting. For cauliflower and broccoli, transplants should be produced in greenhouses with a minimum nighttime temperature of 50°F. Excessive cold, transplant stress, inadequate fertility, or other sources of stress in early stages can cause brassica crops to button. Transplants with thick stems are likely to head prematurely or button. Midseason and late plantings can be transplanted or direct-seeded. If cabbage, broccoli, or cauliflower are direct-seeded, 2-3 weeks should be added to the number of days to maturity.

Generally, coarse-textured soils (sands, sandy loams, etc.) are favored for early plantings because they can be worked earlier in the spring and will warm up faster. These soils are also less likely to become waterlogged under rainy spring conditions. Finer-textured soils that have greater water holding capacity can frequently be used advantageously for producing later crops. 

• Cabbage grown for fresh market should be planted to stand 12-15" apart within rows and 24-36" between rows. For most early or midseason varieties, the closer spacing will give larger yields of smaller heads, which can be a more desirable size for fresh markets. Where direct-seeding, place seed 1/2-3/4" deep and 0.5-1 lb of seed will be required per acre (0.125-0.25 oz per 100 feet of row) depending on variety, seed size, and spacing. Thin seedlings to desired stand when plants are 2-4" tall. Do not allow plants to become crowded.
• Cauliflower should be planted to stand 15-18" apart within rows and 30-36" between rows. Broccoli should be spaced according to market needs. Large single heads can be achieved by a 15-18" spacing. To achieve three-head bunches, which require 5-6" heads with small stalks, plant double row beds with 36" between beds and 10-12" between rows within bed, and 6-9" between plants, depending on variety. Early varieties usually require closer spacing. Southern-grown seedlings can be purchased for transplants, but insect and disease problems often accompany them. If purchasing bare root transplants from nurseries, plant soon upon receipt. Field-grown transplants, once pulled, should not be stored for longer than 9 days at 32°F or 5 days at 66°F prior to planting in the field. Cauliflower and broccoli can be direct-seeded to stand, with precision type planters. Raised beds of 4" are recommended. For cauliflower this will require about 4 oz seed per acre (0.0625 oz per 100 row feet); for broccoli about 0.5 to 1 lb/acre (0.125 to 0.25 oz per 100 row feet).
• Brussels sprouts are most commonly grown from transplants as a long-season crop for fall harvest. Cool weather and light frosts prior to harvest increase quality. Rows are typically spaced 36" apart with 15" spacing within the row. Early and midseason varieties benefit from topping to improve sprout size uniformity if harvesting entire stalks. This should be done once basal sprouts begin to reach marketable size, or around 1900 GDD₅₀. Stripping the foliage from the lower 1/2-2/3 of the plant will allow more light to reach the developing sprouts, as well as increase air circulation, both of which increase sprout quality.
• Kale can be successfully grown from direct-seeding or from transplants. For direct seeding, sow seed at 3-4 lb/A in rows spaced 16-36" apart. Thin to 4-5" apart in the row. Transplants are set in rows 16-36" apart and 6-12" apart in the row. Use wider between-row and in-row spacing for multiple hand harvests by stripping leaves. 
• Kohlrabi may be grown for spring crops by transplants. Transplant into the field at the same time as broccoli or cabbage. Fall crops can be established by direct seeding between June 25 and July 15. Seed open-pollinated varieties at the rate of 2-3 lb per acre and thin to 6-8" between plants in the row. Precision-seed hybrid varieties. Set transplants July 20 to August 15. Space rows 18-24" apart.

Irrigation

Water availability can be critical for successful brassica production. Adequate soil water must be maintained during seedling or transplant establishment and the period of rapid vegetative growth that follows. This is extremely critical prior to head initiation for cabbage, since excessive water applied after cabbage heads have formed can result in split heads. When harvest periods of broccoli and cauliflower occur during times of high temperatures, light overhead irrigation (0.33-0.5") can be used to cool plants and help maintain quality. 

Harvest and Storage

• Cabbage. Harvest as soon as the head has reached full size for the variety grown. Many varieties can hold in the field for considerable periods of time after heading without serious deterioration, but harvest should not be delayed unnecessarily as plants become more susceptible to disease and to splitting.
• Cauliflower heads must be blanched, or protected from sunlight, in order to produce attractive white curd. Some newer varieties are self-blanching or self-wrapping; the inner leaves wrap around the heads during growth. Unless a variety is reported as being self-blanching, when the head is 2-3" diameter, gather the large outer leaves loosely over the head and tie with twine or rubber bands. Tie every 2-3 days with different colored bands to help coordinate harvest dates. Hot, humid, rainy weather after tying can result in a rotting curd. In hot weather, the head should be ready to harvest in 3-5 days after wrapping; in cool weather, blanching takes 8-12 days. Harvest when heads are compact, clear white, and about 6" in diameter. Avoid bruising during harvest and packing.
• Broccoli is harvested when heads are dense and 3-6" diameter, and before individual flower buds are distinguishable or yellow flowers can be seen. Cut 8-10" of stem with the head. Broccoli should be cooled as rapidly as possible and stored under cool conditions after harvest to slow down flower development. Side heads develop rapidly following removal of the terminal head, unless the variety used is a nonsprouting type. Harvesting may continue for several weeks. Broccoli is especially sensitive to postharvest heat and should be hydrocooled or packed on ice immediately after harvest.
• Brussels sprouts should be harvested when sprouts are firm and are of the desired size for market. Sprouts can be harvested individually, working up the stalk as they reach the desired size, or entire stalks can be cut and marketed whole. 
• Kale and collards may be harvested by cutting off entire small plants near ground level, then bunching whole plants. Alternatively, mature leaves may be stripped from plants and either bunched or packed individually. Multiple harvests are possible. 
• Kohlrabi. The targeted harvest stage is when bulbs are full-sized (3" diameter for fresh market, up to 6" for storage) but before they begin to split or become tough and woody. Bulbs are cut with clippers at the soil line, and foliage is trimmed as dictated by markets. Leaves should be removed for long storage varieties.

Many brassica crops are very sensitive to ethylene, and may yellow upon exposure to low levels of ethylene. These crops should be stored as close to 32ºF as possible without freezing, at greater than 95% relative humidity. Air circulation should be adequate to remove heat of respiration, but excessive air circulation will speed transpiration and wilting of leafy crops. Expected storage life varies widely. Consult USDA Handbook 66: The Commercial Storage of Fruits, Vegetables and Florist and Nursery Stocks for crop-specific information.