Cabbage, Broccoli, and Other Cole Crops

Cabbage is grown on all soil types, but does best on well-drained sandy loams with high organic matter. See Soil Managment for a description of ways to increase soil organic matter. A pH of 6 to 6.5 is optimal, although cabbage is sometimes grown at higher pH (pH > 7.2) for clubroot control. Lower pH values will reduce growth.

Soil calcium levels should be 1000 to 2000 ppm and magnesium 150 to 300 ppm. Any lime needed should be added well ahead of planting. Soil Management describes types of liming materials and their effect on soil pH, and Ca and Mg availability. Low calcium in the soil can cause tipburn, but this physiological disorder can also occur if calcium is unavailable because of drought or flooded soil, or when soil fertility is high. More information on tipburn and other physiological disorders is presented later in this chapter.

Like most leafy vegetables, cabbage has a high nitrogen requirement. Too little nitrogen reduces yields, shortens storage life, delays maturity, and can increase the 'cabbagey' flavor to objectionable levels. Too rapid growth at high nitrogen, however, is likely to lead to coarse, loose heads, cracking, tipburn, and poor processing and storage quality. Red cabbage needs an additional 10 lb actual nitrogen per acre per side-dressing. This nitrogen requirement can be satisfied by a wide variety of soil amendments, as well as conventional fertilizers. See Soil Management for a description of organic sources of nitrogen and their approximate nitrogen content.

Harvesting one ton of cabbage removes 4 to 9 pounds N, 1 to 4 pounds P2O5, and .8 to 1.3 pounds K2O from the soil. Fertilizer recommendations for cabbage based on soil tests are presented in Cole crop nutrient recommendations based on soil tests. Organic sources of these nutrients are listed in Soil Management. Typically, if soil test results indicate a need for high analysis N-P-K, half the amount should be broadcast and half banded to reduce the potential for salt injury to roots from the banded material. Preplant applications are followed three weeks after transplanting by a sidedressing of 25 to 30 pounds of nitrogen. Cole crops have a high boron requirement. Symptoms of boron deficiency vary with the cole crop attacked. Cabbage heads may simply be small and yellow. Most cole crops develop cracked and corky stems, petioles and midribs. The stems of broccoli, cabbage and cauliflower can be hollow and are sometimes discolored. Cauliflower curds become brown and leaves may roll and curl. If boron is added, and beans or other boron sensitive crops follow cabbage in a rotation, a soil test is advisable before planting to ensure that boron levels are not too high.

Planting

Cover crops and conservation tillage are often used with cabbage, especially in hilly areas where the potential for erosion is high. Cabbage is usually transplanted in no-till situations to increase early growth. See Chapters 2 and 3 for a description of these techniques.

With conventional tillage practices, seeds can be planted directly in the ground or the crop can be established using transplants. In the field, seeds are placed 1 to 2 inches apart in rows 36 to 42 inches apart, ¹- to ¸-inch deep and are thinned to 9 to 14 inches apart. This spacing will produce a high percentage of 2-to-3-pound heads which are preferred for fresh market production. Using double rows per bed (or streaks per row) will increase yields 50 to 70 percent and improve harvest efficiency. With double streaks, spacing must be changed to 14 to 18 inches and plants must be staggered in the row, with 12 inches between streaks.

Direct seeding is most common for fall crops when the soil is warm and emergence and early growth is rapid. The spring crop is usually started from transplants, using seedling final-stand spacings. Transplants can be overwintered but if seedlings larger than ¹ inch are exposed to low temperatures (32 to 45 degrees F for extended periods), flowering can be induced, which results in bolting rather than production of a head. See the discussion of buttoning in broccoli for an additional discussion of low temperature induction of flowering.

If not overwintered, transplants are typically set out three weeks before the last frost date. Optimal transplant size for either fall or spring planting is 4 to 6 true leaves. Deep planting has been shown to increase yields in once-over harvested cabbage.

Harvest and Storage

In North Carolina, 85 to 90 days from transplanting to harvest is typical. Heads should be firm-to-hard at harvest, but delaying harvest may increase the risk of splitting mature heads if soil moisture increases suddenly. Two-to-three pound heads are cut at the base and the outer leaves are trimmed off. For the fresh market, fields may be cut 3 to 5 times. Hybrids are preferred for commercial production because a higher percentage of the plants can be harvested at any one time, thus reducing the total number of harvests. Cabbage is packed in wirebound containers or sacks weighing approximately 50 pounds.

Heads must be cooled immediately after harvest. Cabbage can be stored at 32 to 36 degrees F and 95 percent relative humidity for 3 to 6 weeks (early crop) or 5 to 6 months (late crop). Storage life can be prolonged even further at low O2 (2 percent) and high CO2 (5 percent) and with controlled atmosphere storage systems. Bacterial soft rot is the main problem in storage. Since fresh cabbage is available almost year-round, for the most part, only special cultivars used for sauerkraut processing are stored.