Soil texture is not critical, but early cabbages do best in a sandy loam, while later types prefer a heavier, moisture-retaining soil. Side-dress seedlings with rich compost 3 weeks after planting. Hand pull weeds to avoid damaging cabbage's shallow roots; use a mulch to keep the soil moist. Uneven watering can cause a sudden growth spurt that will make the developing head split. If you see a cabbage head starting to crack, twist the plant a half turn and pull up to slightly dislodge the roots and thus slow the plant's growth. Or use a spade to cut the roots in one or two places 6 inches below the stem. This also helps to prevent cabbage from bolting (producing a flower stalk).
Avoid wetting the foliage during cool weather or periods of high humidity, because constantly wet leaves are prone to disease. Cut back on water as cabbage matures. If leaves start to yellow, provide a mid-season nitrogen boost with compost tea. See the Compost entry for instructions for making compost tea. This type of feeding can also encourage a slow-growing crop to mature before hot weather or a winter freeze sets in.
Major cabbage pests include cabbage maggots, imported cabbageworms, cabbage loopers, and cutworms. The harlequin bug, a small shiny black insect with red markings, causes black spots and wilting leaves; control by hand picking or applying insecticidal soap. Slugs may chew ragged holes in leaves.
Black leg, a fungal disease, forms dark spots on leaves and stems. Black rot symptoms include black and foul-smelling veins. Club root prevents water and nutrient absorption. Fusarium wilt, also known as yellows, produces yellow leaves and stunted heads. Remove and destroy plants affected by these diseases. If club root has been a problem in your garden, test soil pH before planting and add ground limestone if needed to raise the pH to at least 6.8
Good growing conditions, crop rotation, and the use of disease-resistant cultivars are the best defenses against cabbage-family crop problems. Also, thoroughly clean up the garden at the end of the season, removing all remaining leaves and roots.
Use a sharp knife to cut heads when they are firm. Leave stalks and roots in place to produce tasty little cabbages; eat them like Brussels sprouts or let them develop into a second crop of small heads. Fresh cabbage has the best taste, but late-season cultivars keep well in a moist, cool place (32° to 40°F) for 5 to 6 months. Use split heads for making sauerkraut.