Napa Cabbage

At a glance

Tip for beginners: Grow it as a fall crop only in your first year, sow on the 11-week date, and put row cover over the bed the same day — most first-year failures come from spring planting or from flea beetles on unprotected seedlings

Main challenge: Timing: sown too early it meets summer heat, sown too late it runs out of season before heading, and spring plantings often bolt after cold nights

When to plant

• Sow, 11 weeks before your first fall frost.

What can go wrong

• Bolting instead of heading. A flower stalk pushes up through the center before a firm head forms. Young plants exposed to a week or more of nights below 50°F, or to frost, can be triggered to bolt later; long, warm days push it further. This is why spring crops fail often and fall crops usually do not.
• Tipburn. Brown, dry edges on the inner leaves, often found only when the head is cut. Caused by poor calcium movement into fast-growing leaves during uneven watering or heat. Keep soil evenly moist and avoid heavy nitrogen late in heading.
• Clubroot. Plants wilt in the afternoon, look stunted and yellow, and have swollen, club-shaped roots. A soilborne disease favored by acidic, wet soil that persists for many years. Rotate brassicas, lime toward pH 7.2 in affected beds, and grow resistant varieties.
• Flea beetle damage on seedlings. Small round holes across young leaves in late summer. Heavy feeding can stall or kill seedlings. Cover the bed with row cover from sowing or transplanting.
• Cabbage worms and loopers in the head. Green caterpillars chew ragged holes and leave dark droppings between leaves, deep inside the head. Row cover prevents egg-laying; Bt sprays work on young caterpillars before they move inside.
• Slugs and soft rot in wet fall weather. Slugs hide in the lower leaves and their feeding opens the way for bacterial soft rot, which turns the base slimy and foul-smelling. Remove damaged outer leaves, keep the bed free of debris, and harvest before long cold, wet spells.

Growing guide

In Korea, cabbage for kimjang kimchi is sown as summer winds down and cut as the nights turn cold, and that calendar carries over well to most US gardens. Napa cabbage has a narrow comfort range. It grows best with days in the 60s °F, it tends to bolt if young plants sit through a week or more of nights below 50°F, and it tends to bolt or rot in summer heat. A spring crop has to dodge both problems at once. A fall crop starts warm and finishes cool, the order the plant prefers, which is why napa is mainly a fall vegetable in the US.

Sow about 11 weeks before your first fall frost. You can direct sow three or four seeds every 12 to 18 inches and thin to one plant, or start seeds in cell trays and set them out three to four weeks later. Napa sulks after root disturbance, so move transplants with the root ball intact and water them in. Give round, barrel-shaped heads about 18 inches; tall Michihli types and minis can go at 12. Full sun suits the fall crop, but in hot regions late-summer seedlings may need shade cloth for their first week or two.

Napa is fast and hungry. It can build a head of several pounds in about two months, so steady water and nitrogen matter more than with most brassicas. Aim for about an inch of water a week, more during hot spells, and side-dress with nitrogen three to four weeks after transplanting or thinning. Uneven watering shows up as tipburn: brown, papery edges on the inner leaves that you often find only after cutting the head open. Tipburn is a calcium shortage inside the leaf, usually caused by fast growth during uneven moisture rather than a lack of calcium in the soil, so steady watering prevents more of it than extra lime does.

Pests arrive early. Flea beetles can riddle late-summer seedlings with small holes, and cabbage worms and loopers feed their way into the head, where they are hard to wash out before making kimchi. Row cover laid over the bed on the day you sow or transplant, and left on until the weather cools, keeps out most of both. Clubroot is the disease to worry about in acidic soil. Plants wilt on warm afternoons, recover overnight, and show swollen, knotted roots when pulled. Its spores can survive in soil for many years, so rotate all cabbage-family crops, raise the pH toward 7.2 in beds where it has appeared, and look for resistant varieties such as Bilko. If you try a spring crop, choose a slow-bolting variety, keep seedlings warm indoors, and plant out only once nights stay above 50°F; it often bolts anyway.

Harvest when the head feels firm when you squeeze it from top to bottom, and cut it at the base with a knife. Mature heads usually handle a light frost, but a hard freeze in the low 20s can damage the outer leaves and lead to rot, so cut before such a forecast. For kimchi, heads that have been through a few cool nights tend to be sweeter. Trimmed heads wrapped in newspaper can keep one to two months near 32°F with high humidity, which is longer than most people expect from such a tender-looking vegetable.

Harvest and keep