How to Grow Chinese Cabbage in Australia

Chinese cabbage (Brassica rapa subsp. pekinensis), also called wombok or napa cabbage, is in the cabbage family, Brassicaceae, grown for crisp, mild heads. A cousin of turnip and bok choy rather than a true cabbage, it matures faster than a drumhead type and takes less room. Most failures come from timing: cold makes young plants run to flower, and heat softens and rots the heads.

Three mistakes that matter

1. Sowing into cold weather. Young plants chilled by days averaging below about 15°C often start bolting (sending up a flower stalk) before the head fills. Sow inside your zone's window, and choose a slow-bolt variety for spring.
2. Letting the soil dry out. Chinese cabbage is shallow rooted, so a dry spell stops growth, toughens the leaves and can push plants to flower. Water deeply every day or two in warm weather and keep mulch topped up.
3. Planting out old seedlings. Transplant shock is a common trigger for bolting, and seedlings left too long in their cells suffer it most. Plant out at three to four weeks, or sow direct in spring when bolting risk is highest.

When to plant

Seed germinates in soil between about 10°C and 24°C, but air temperature over the next two months decides the crop. Plants grow best when days average 15°C to 24°C; above a 25°C average, heads stay small and rot easily. Sow a short row every three weeks rather than one big bed, so heads do not all mature at once.

At the cold edge of a window, sow a slow-bolt variety and protect seedlings from cold winds. At the hot edge, cover young plants with shadecloth. Queensland's Lockyer Valley grows commercial crops through autumn, winter and spring, missing the summer heat.

Site, soil and setup

Give Chinese cabbage deep, rich soil that holds moisture yet drains freely, because its shallow roots dry out and rot easily.

Rotate beds so no broccoli, cauliflower, kale, cabbage, bok choy or turnip has grown there for three to four years. The soil pH article explains testing and liming.

Container growing

One head needs a pot at least 30 cm across and 30 cm deep, holding 18 L or more of premium potting mix. The mini types suit pots best: 'Mini Napa', 'Little Dragon' and the loose-leaf 'Tokyo Bekana'.

• Water: daily in warm weather, until water runs from the base, as pots dry faster than beds.
• Feed: fish and seaweed blend at 25 mL per 9 L, fortnightly, or an all-purpose soluble (NPK around 23-4-18) at the label rate.
• Position: move the pot into afternoon shade in warm weather, with mesh over it.

Sowing Seeds

Cells give a more even stand late in the season, and direct sowing spares spring crops transplant shock. Space plants as the Thinning table gives for each type.

Starting under cover

• Sow two or three seeds per cell, 5 to 10 mm deep, in seed-raising mix.
• Keep the mix moist; seedlings appear in 4 to 10 days.
• Plant out when seedlings carry four or five true leaves, before roots circle the cell.
• Harden off (move seedlings outside for longer each day over about a week) before planting.

Sowing direct

Sow two or three seeds at each station, 5 to 10 mm deep, and keep the soil damp until they emerge. Thin them as Thinning describes.

Planting out

• Plant at the same depth as in the cell and firm the soil around each stem.
• Water in with seaweed solution at half strength, 15 mL per 9 L, to ease transplant shock.
• Mulch with straw once plants settle, which also stops rain splashing soil onto the leaves.

Care by growth stage

Fast, unchecked growth makes a firm head: steady water, nitrogen while leaves build, then no extra nitrogen once the head fills. Weeks count from planting out; for a direct-sown crop, count from about three weeks after sowing.

Insect mesh keeps out butterflies only if its edges are weighed down with bricks or soil. It also keeps out the birds and predators that clean up sap suckers, so check under it weekly for aphids and whitefly.

Thinning

Thinning sets head size, because crowded plants make small heads and hold the damp air that soft rot needs.

• Cells: snip all but the strongest seedling at soil level, so the roots left behind are not disturbed.
• Direct-sown stations: thin to one seedling at two or three true leaves.
• Thinnings: rinse and eat them in salads.
• Cool, wet spells: strip yellowing and dead lower leaves and bin them, so rot has nothing to start on.

Companion planting

Low neighbours share the bed without shading it, and flowering herbs feed the insects that hunt caterpillars and aphids.

Grows well with

• Onions and spring onions, which break up a block of brassicas so butterflies find it less easily.
• Dill and coriander left to flower, whose flowers feed parasitic wasps and hoverflies.
• Lettuce, silverbeet, celery and dwarf beans, low crops that do not shade the heads.

Keep apart

• Mustard, bok choy and other brassicas in one solid block, which share caterpillars, aphids and clubroot.
• Climbing beans and staked tomatoes, tall plants that shade the bed.

Harvesting Heads

Cut a head once it feels firm and solid when squeezed. That is usually 8 to 12 weeks from sowing, or about 8 weeks from planting out, depending on variety.

• Cut the whole head at its base with a sharp knife.
• Strip loose outer leaves until those left wrap the head tightly.
• Cut in the cool of the morning on a dry day, as wet heads rot easily.
• Pick spring crops before summer heat, and autumn crops before hard frost.
• Take 'Tokyo Bekana' a few leaves or a bunch at a time; it regrows for more cuts.
• Pull any plant showing a flower stalk and use it straight away.

Cool a cut head quickly, wrap it unwashed and keep it in the fridge crisper, where it often lasts several weeks and up to six. Shred it into slaw, stir-fry it, or add it to soups and hotpots. For kimchi, follow a tested recipe, as vegetables preserved at home need the right salt and acidity to prevent botulism.

Common problems

Brown, papery edges on the inner leaves. Tipburn is a calcium shortage in fast-growing inner leaves. Uneven or too little water, heat, salty water or heavy nitrogen cause it, even in soil with enough calcium. Calcium sprays help little unless watering is fixed.

Black specks on the white midribs. Gomasho is a physiological disorder of the cooler months that heavy nitrogen makes worse. Keep side-dressings to the rates in Care by growth stage.

Loose, open heads. Heat, overcrowding and too much nitrogen all stop leaves folding into a head, and 'Tokyo Bekana' never forms one. For heads that split open around a flower stalk, see Three mistakes that matter.

Seedlings collapsing at soil level. Damping off is favoured by wet mix, crowding and still air. Read more

Yellow patches with white fluff under seedling leaves. Downy mildew spreads in crowded trays in cool, damp weather; space trays so air moves, and avoid watering in the morning. Read more

Holes chewed overnight. Snails and slugs graze seedlings and hide between the outer leaves of older plants, especially in damp autumn weather. Pick them off by torchlight, set beer traps, or scatter an iron-based snail bait as the label directs. Read more

Pests and diseases

Few sprays are registered for Chinese cabbage itself, so use only those whose label covers brassica crops.

Cabbage white butterfly (Pieris rapae). Its dull green caterpillars grow to about 25 mm and chew holes through the leaves. Pick them off, or spray Bacillus thuringiensis, a bacterial insecticide that affects only caterpillars, as the label directs. Loopers and native budworm (Helicoverpa punctigera) chew similar holes, and the same spray controls them. Read more

Diamondback moth (Plutella xylostella). Also called cabbage moth, its larvae grow to about 10 mm and graze clear windows into leaves. It resists many insecticides, so mesh and regular checks matter most. Read more

Cabbage aphid (Brevicoryne brassicae). Grey, mealy colonies curl leaf edges and cluster around the growing point, most in spring and autumn. Aphids also spread turnip mosaic virus, so hose them off and spray insecticidal soap as the label directs. Read more

Vegetable weevil (Listroderes difficilis). Its cream to green grubs, up to 12 mm long, feed at night from autumn to early spring and burrow into heads. Search by torchlight, or in the soil and growing point by day, and clear weeds such as capeweed before planting. Read more

Bacterial soft rot (Pectobacterium carotovorum). A grey, watery, foul-smelling rot starts at the base of the lower leaves and collapses the plant, worst in hot, wet weather. There is no cure, so pull affected plants and bin them.

Clubroot (Plasmodiophora brassicae). This soil-borne disease swells roots into galls, so plants wilt on warm days and stunt. It survives in soil for many years and favours acid soil. Bin affected plants with their roots, never compost them, and lime as Site, soil and setup describes.

Prevention first

• Space plants at full distance so leaves dry quickly after rain.
• Turn a few leaves at least weekly for eggs, caterpillars and aphids.
• Pull brassica weeds near the bed, which host the same pests and diseases.
• Weed carefully and clean your knife between plants, since soft rot enters through wounds.

Tips

1. Once a plant is half grown, lift its outer leaves and tie them loosely upright with raffia or soft cloth. New leaves fold over inside and start the head earlier.
2. While heads form, pick a few outer leaves from each plant for salads and wraps, leaving the centre untouched.
3. To save seed, grow an open-pollinated type such as 'Kyoto' or 'Tokyo Bekana' and let at least five plants flower together. Take the mesh off when they flower, as insects carry the pollen. Chinese cabbage crosses with bok choy, turnip and mizuna, so keep other kinds 250 m away; the F1 hybrids do not come true.