How to Grow Kale in Australia

Kale (Brassica oleracea) is a leafy member of the cabbage family, Brassicaceae, grown for leaves picked a few at a time over many months. The Russian and Siberian kales belong to a close relative, Brassica napus. It shrugs off frost and sweetens in the cold, so it carries the vegie patch through the cool months in every Australian zone. A common mistake is leaving it unnetted, because the caterpillars of the cabbage white butterfly (Pieris rapae) find it first.

Three mistakes that matter

1. Leaving plants uncovered. Cabbage white butterflies seek out young kale, and their caterpillars chew leaves to the midrib. Cover the bed with insect mesh on hoops at planting.
2. Growing it through the heat. Kale pushed into summer turns bitter, runs to flower and draws caterpillars; Queensland advises against summer brassicas in hot districts such as the Lockyer Valley. Sow inside your zone's window so leaves grow through the cool months.
3. Picking from the centre. New leaves come from the growing tip, so cutting it or stripping a plant bare stalls the harvest. Take the lowest outer leaves and leave the tip and a crown of young leaves to keep it cropping.

When to plant

Kale seed germinates in soil between 8°C and 30°C, so heat, not cold, sets the calendar. Sow so plants reach picking size as the weather cools, and sow a second batch later in the window to stretch the harvest.

At the hot edge of a window, raise seedlings in punnets in a shaded spot and plant out once nights cool. In southern gardens, aim to have autumn seedlings in by Anzac Day, so they size up before winter slows them.

Site, soil and setup

Grow kale in firm, rich soil that drains, where no cabbage, broccoli, cauliflower, Brussels sprouts, kale or mustard has grown for three years.

Liming matters for kale because clubroot, one of the most destructive brassica diseases, favours acid soil. The soil pH article explains how to test and adjust.

Container growing

One plant needs a pot at least 30 cm across and 30 cm deep, about 20 L, filled with premium potting mix. Compact types suit pots best, such as 'Dwarf Siberian Improved' and 'Premier'.

• Water: whenever the top of the mix feels dry, until water runs from the base.
• Feed: fish and seaweed blend at 25 mL per 9 L, fortnightly.
• Position: full sun in the cool months, with afternoon shade in warm zones and a mesh cover over the pot.

Sowing Seeds

Raise kale in punnets and plant out at four to six weeks, or sow direct in mild weather. Either way, plants stand 40 to 50 cm apart.

Starting under cover

• Sow 6 to 10 mm deep in seed-raising mix, two or three seeds per cell.
• Keep the mix moist but not wet; seedlings appear in 3 to 10 days.
• Give full light from the day they emerge, so stems stay short and sturdy.
• Harden off (move seedlings outside for longer each day over about a week) before planting.

Sowing direct

In mild weather, sow two or three seeds at each station, 6 to 10 mm deep. Firm the soil over them and keep it damp until they come up.

Planting out

• Plant at the same depth as in the punnet and firm the soil around each stem.
• Water in with seaweed solution at half strength, 15 mL per 9 L.
• Mulch with straw once plants settle, clear of the stems.

Care by growth stage

Steady moisture and nitrogen for leaf decide this crop. Weeks count from planting out.

Insect mesh works only if butterflies cannot get under it. Weigh the edges down with bricks or soil. Open it early in the morning or late in the afternoon, when butterflies are not flying. White butterfly decoys on sticks generally do not stop egg laying.

Thinning

Thinning sets how big each plant grows and how well air moves through the bed. Crowded seedlings are the ones downy mildew hits hardest.

• Punnets: snip all but the strongest seedling in each cell with scissors, so the roots left behind are not disturbed.
• Direct-sown stations: thin each clump to one seedling once true leaves show.
• Thickly sown rows: pull thinnings for salads, leaving plants at full spacing.
• Yellowing lower leaves: strip them off and bin them, so the base of the plant stays airy and clean.

Companion planting

Good neighbours break up a solid block of brassicas and feed the insects that hunt caterpillars and aphids.

Grows well with

• Onions and spring onions, which break up the bed so butterflies find the kale less easily.
• Dill and coriander left to flower, whose flowers feed parasitic wasps and hoverflies.
• Beetroot, celery and dwarf beans, lower crops that share the bed without shading kale.

Keep apart

• Mustard and other brassicas in a solid block, which share caterpillars, aphids and clubroot.
• Climbing beans and staked tomatoes, tall plants that shade a winter crop.

Harvesting Leaves

Start picking 7 to 10 weeks from sowing, once the plant carries a full crown of leaves. Baby leaf from thickly sown rows is ready from about 5 weeks.

• Pick the lowest, outer leaves first and work up the stem.
• Snap or cut each stalk cleanly where it meets the main stem.
• Leave the growing tip and the young inner leaves every time.
• Take a few leaves from each plant rather than stripping one.
• Pick in the cool of the morning, when leaves are crisp.
• In spring, pick the young flower shoots and cook them like broccoli.

Keep leaves unwashed in a bag in the fridge crisper and use them within a week or two. Steam or stir-fry them, add them to soups, or bake them into chips; young Russian leaves suit salads.

Common problems

Plants running to flower. Kale is a biennial (a plant that flowers in its second year). Once plants have been through winter cold, warming spring weather sends up flower stems and turns leaves bitter.

Coarse, strong-tasting leaves. Old leaves left on the plant and dry soil toughen kale, so pick regularly and water steadily. For heat, see Three mistakes that matter.

Patchy emergence in the bed. Kale seed sown straight into garden soil often comes up unevenly, which is why punnets give a better stand.

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

Tall, floppy seedlings. Seedlings raised in poor light stretch towards it and fall over when planted out. Read more

Seedlings chewed to the ground overnight. Snails and slugs graze new plantings at night after rain, leaving silvery trails. Pick them off by torchlight or sink a shallow beer trap. Read more

Pests and diseases

Kale's usual pests are caterpillars and aphids, and its diseases follow acid, wet soil or cool, damp weather.

Cabbage white butterfly (Pieris rapae). Its velvety green caterpillars chew large holes in leaves, and one female can lay up to 800 eggs. Pick off caterpillars, or spray Bacillus thuringiensis, a bacterial insecticide that affects only caterpillars, while they are small and as the label directs. It can also harm other butterflies and moths, so spray the kale alone. Read more

Diamondback moth (Plutella xylostella). Also called cabbage moth, it has bright green caterpillars about 10 mm long that feed under leaves, leaving clear windows that tear into holes. Numbers build from spring to autumn, worst in dry summers. Read more

Cabbage aphid (Brevicoryne brassicae). Dull grey-green aphids up to 3 mm long form blue-grey colonies coated in whitish powder, peaking in late winter and early spring. Hose them off, then spray insecticidal soap under the leaves as the label directs. Read more

Clubroot (Plasmodiophora brassicae). This soil-borne disease swells roots into knobbly galls, so plants yellow, wilt and stunt. Spores can survive up to 20 years. Bin affected plants with their roots and never compost them; liming is in Site, soil and setup.

Downy mildew (Hyaloperonospora parasitica). Yellow patches on the leaf carry greyish-white growth underneath, worst on young plants in cool, damp weather. Water at the base early in the day so leaves dry quickly. Read more

Prevention first

• Space plants at full distance so leaves dry quickly after rain.
• Turn a few leaves twice a week for eggs, caterpillars and aphids.
• Pull brassica weeds such as shepherd's purse and wild mustard, which host clubroot and aphids.
• Scrape soil off boots and tools after working a bed with clubroot, as the spores travel in soil.

Tips

1. Turn a plant into a kale tree that crops for several years. Pick only mature leaves, strip the small leaves along the stem, and cut off flower heads in the warm months.
2. When an old kale tree flops or slows, cut it back to just above a node near the base and let it reshoot.
3. Do not pull a summer-battered plant. Keep removing the worst leaves, and it often returns to vigorous growth as autumn cools.
4. Curled and Tuscan kales cross readily with cabbage, broccoli and cauliflower, so save seed only from one variety flowering on its own.