How to Grow Cabbages in Australia

Cabbage (Brassica oleracea var. capitata) is a leafy vegetable in the cabbage family, Brassicaceae, grown for its tight head of folded leaves. It is a cool-season crop that suits autumn and winter in the north and most of the year in the south. The usual failure is leaving young plants uncovered, so caterpillars strip them before a head can form.

Three mistakes that matter

1. Sowing for the wrong season. A head that has to form in hot weather often splits or runs to seed, and caterpillars peak with the heat. Time each sowing so heads form in the cool months, using the table in When to plant.
2. Planting out without netting. Cabbage white butterflies (Pieris rapae) and diamondback moths (Plutella xylostella) lay eggs on seedlings from the first day. Cover plants with fine insect mesh on hoops at planting, with the edges weighed down, and keep it on.
3. Watering in fits and starts. Dry spells leave heads loose, tough or bitter, and a soaking after a dry spell splits a firm head. Give about 25 mm a week as deep soaks, under straw mulch.

When to plant

Cabbage seed comes up in soil anywhere from about 7°C to 35°C, but heads form best in mild, cool weather. Count back from the cool months, since most types need 8 to 20 weeks to head. Sow a short row every few weeks for a run of heads rather than a glut.

At the warm edge of a window, choose a quick conical or early round type. At the cold edge, start seed in trays under cover and plant out once the seedlings reach size.

Site, soil and setup

Cabbages are heavy feeders that sit in one spot for two to four months, so give them the best-fed bed in the garden.

Where clubroot has shown before, lime the bed to about pH 7.0 three months ahead. Its spores germinate poorly at that pH. Test the soil first, because too much lime locks up other nutrients.

Container growing

One cabbage needs a pot at least 30 cm deep and 30 cm across, holding about 18 to 20 L. Fill it with premium potting mix blended with compost. Compact early types suit pots best: 'Golden Acre', 'Mini', 'Red Express' and the conical 'Sugarloaf'.

• Water: whenever the top 2 cm of mix is dry, which is daily in warm weather.
• Feed: fish and seaweed blend at 25 mL per 9 L fortnightly from two weeks after planting.
• Position: as in Site, soil and setup; move the pot into afternoon shade in warm spells.

Sowing Seeds

Most gardeners raise cabbage in trays, which saves bed space and keeps tiny seedlings away from slugs.

Starting in trays

• Sow 5 mm deep in seed-raising mix, two seeds to a cell.
• Keep the mix moist; seedlings show in 4 to 14 days.
• Snip the weaker seedling in each cell once the first true leaf shows.
• Plant out at 4 to 6 weeks, when seedlings stand 7 to 10 cm tall with four or five true leaves.

Sowing direct

Direct sowing works in mild weather but takes longer: direct-sown cabbages can need up to three weeks more to head than transplants. Sow two or three seeds per station at the spacing in the table below, then thin to the strongest.

Transplanting

Spacing depends on how big the head grows, so check the type before you plant. Rows sit about 60 cm apart.

• Harden off (accustom seedlings to sun and wind over about a week) before planting.
• Plant into moist soil, firm it well around each stem, and water in with seaweed solution at the rate in Care by growth stage.
• Mulch with straw, clear of the stems.

Care by growth stage

Steady water and steady nitrogen decide the size and density of the head. Weeks count from planting out for a mid-season type; quick types move through faster and late drumheads slower.

That 25 mm is 25 L per square metre; sandy soils take it in smaller, more frequent drinks. Too much soluble nitrogen late in the season makes soft growth that aphids favour, which is why feeding stops at the firm head.

If you prefer a conventional feed, mix a controlled release granular (NPK around 14-5-10) into the bed at planting. From week three, water on an all-purpose soluble (NPK around 23-4-18) fortnightly until heads start to firm. No potassium-rich flowering feed is needed, since the head is cut before the plant flowers.

Keep the mesh on until harvest, but lift it once a week to check under the leaves. It keeps out the birds and wasps that eat caterpillars, so a few pests that slip inside can build up unseen.

Thinning

Cabbages need no pruning, only thinning and tidying. Crowded seedlings stretch and head poorly, and old leaves left lying about carry disease.

• Snip spare seedlings with scissors rather than pulling them, so the roots of the keeper stay undisturbed.
• Remove yellowing lower leaves as they appear, and bin any with spots or fuzz.
• Pull any plant with wilting, stunted growth and check its roots for clubroot swellings.
• After cutting a head, leave the stump to sprout, then keep the few strongest shoots.

Companion planting

Good partners either confuse the cabbage white butterfly or share none of the cabbage's pests.

Grows well with

• Dill, sage and coriander, whose strong scent the cabbage white butterfly avoids.
• Celery between the rows, another strong scent the butterfly is reported to dislike.
• Onions and beetroot, which share neither clubroot nor the brassica caterpillars.
• Land cress at the far end of the garden, a decoy that draws the butterflies' eggs away.

Keep apart

• Broccoli, cauliflower, kale and Chinese cabbage in the same bed, which share clubroot, black rot (Xanthomonas campestris) and diamondback moth.
• Mustard grown as a cover crop just before cabbage, since it is a brassica that feeds the same pests.
• Wild radish and wild turnip weeds, which carry black rot and clubroot between crops.

Harvesting Heads

Cut when the head feels firm and dense under a pressing hand, at the size the variety is known for.

• Cut with a sharp knife just under the head, leaving the outer wrapper leaves on the stump.
• Cut spring-planted heads before hot weather splits them or makes them bolt.
• Cut autumn-planted heads before severe frosts.
• When the bed is finished, pull and bin the stumps and roots rather than leaving them to reshoot.

A firm, undamaged head keeps for several weeks somewhere cool and humid, such as the crisper drawer of the fridge. Keeping it for months needs about 0°C to 4°C at high humidity, much damper than a home fridge.

Shred it raw into coleslaw, stir-fry it, or roll the leaves around a filling.

Common problems

Split heads. A firm head cracks open after uneven watering (see Three mistakes). Once it is firm, give the plant a quarter turn or push a spade into the soil on one side to slow the water.

Running to seed. A stem pushes up through the head and flowers, usually from heat, or from sizeable plants set out into a long cold snap. Cut the head at once and see When to plant for timing.

Loose or no heads. Heads stay open when plants go short of water or food, are sown too late, or are crowded. See Three mistakes and Care by growth stage.

Seedlings chewed overnight. Ragged holes and silvery trails point to slugs and snails, which take newly planted cabbages first. Read more

Pests and diseases

Check for these three insects and three diseases each time you lift the mesh.

Cabbage white butterfly (Pieris rapae). A white butterfly with black wing spots lays eggs under leaves, and the well-camouflaged green caterpillars chew large holes and leave green droppings. Check under leaves, squash eggs and caterpillars, and use a Bacillus thuringiensis (Bt) caterpillar spray for heavy numbers. Read more

Diamondback moth (Plutella xylostella). Often called cabbage moth. Its pale yellowish-green caterpillars, up to 12 mm, chew small holes that leave a see-through window and tunnel into heads. It has become resistant to many insecticides, with synthetic pyrethroid resistance found in every Australian state, so rely on mesh and weekly checks. Read more

Cabbage aphid (Brevicoryne brassicae). Dense blue-grey colonies, dusted with whitish powder, cluster on young leaves and in the heart, and they spread plant viruses. Hose off small colonies or use insecticidal soap, and leave the puffed-up, parasitised aphid mummies, which mean tiny wasps are at work. Read more

Clubroot (Plasmodiophora brassicae). Roots swell into distorted clubs, and plants stunt, yellow and wilt on warm days. The spores last in soil for many years. Bin affected plants with their roots, then lime and rotate as in Site, soil and setup.

Black rot (Xanthomonas campestris). Yellow V-shaped patches run in from the leaf edges, and cut veins show black. It spreads in splashing water and on seed, so remove affected plants promptly.

Downy mildew (Hyaloperonospora parasitica). Yellowish patches on the upper leaf match white fluffy growth beneath, and old patches turn brown and papery. It needs wet leaves and cool, damp weather, so remove affected leaves early. Read more

Prevention first

• Plant clean seedlings from your own trays or a reliable source, into a limed, rotated bed.
• Water at the base so leaves stay dry, since black rot splashes and downy mildew needs wet leaves.
• Check leaf undersides and the heart once a week.
• Pull brassica weeds and bin spent plants rather than composting diseased ones.

Tips

1. Sow an early type and a late type on the same day for a longer run of heads.
2. White plastic butterfly shapes on stakes may deter the cabbage white, which tends to avoid landing where another is feeding.
3. Chinese cabbage, or wombok (Brassica rapa), and Ethiopian cabbage (Brassica carinata) are different species with their own needs, so grow them by their own guides.