How to Grow Collards in Australia

Collards (Brassica oleracea, Acephala group) are a leafy vegetable in the cabbage family, Brassicaceae, grown for broad leaves picked one at a time for months. They are the same species as kale and cabbage but form no head. They also handle heat better than either, so they suit northern gardens as well as southern ones. The usual mistake is letting caterpillars get a start on the young leaves.

Three mistakes that matter

1. Letting caterpillars get ahead. Cabbage white butterfly and diamondback moth caterpillars feed under the leaves and can leave young plants full of holes. Check the undersides twice a week from planting and act on the first eggs or caterpillars, as set out in Pests and diseases.
2. Planting too close. Collards grow into broad plants, and crowded ones give smaller leaves and hold the damp, still air that downy mildew needs. Give each plant the room shown in Thinning.
3. Stripping the plant. Cutting off the top, or taking most of the leaves at once, stops the plant cropping again. Pick the lower, outer leaves and leave the top rosette growing, as described in Harvesting Leaves.

When to plant

Collard seed germinates in soil from 8°C to 30°C, usually in 3 to 7 days, so soil temperature seldom holds a sowing back. The better guide is the pests and the weather: caterpillars are most active from spring to autumn, and frost sweetens the leaves. One sowing crops for months, so most gardens need only one or two sowings a year.

In southern gardens, seedlings raised in trays in March are ready to plant out around Anzac Day. A late winter sowing can take over when autumn-sown plants flower in spring; see Common problems.

Site, soil and setup

Plant collards where beans, onions or tomatoes grew, never after kale, cabbage, broccoli or mustard. Clubroot spores can survive in soil for up to 20 years.

Container growing

'Vates' is the collard for a pot, since it stays about 30 to 40 cm tall. Grow one plant in a pot of at least 20 L and 30 cm across. Give it drainage holes and fill it with premium potting mix. 'Georgia Southern' grows too large for most pots and does better in a bed.

• Water: pots dry out faster than beds, so check them daily in warm weather and water before the mix dries out.
• Feed: from three weeks after planting, fish and seaweed blend at 25 mL per 9 L, fortnightly.
• Position: full sun in the cool months; move the pot into afternoon shade during hot spells.

Sowing Seeds

Raise collards in trays and plant them out at 4 to 6 weeks, or sow them where they are to grow and thin them.

Choosing a variety

Starting in trays

• Sow two seeds per cell of seed-raising mix, 5 to 10 mm deep.
• Keep the mix damp; seedlings usually emerge in 3 to 7 days.
• Snip the weaker seedling in each cell at mix level.
• Plant out at 4 to 6 weeks, when seedlings are 5 to 10 cm tall.
• Harden them off first (a week of gradually longer spells outdoors); see hardening off seedlings.

Sowing direct

• Rake the bed to a fine surface and water it the day before.
• Sow two or three seeds per station, 5 to 10 mm deep, with stations at the spacing in Thinning.
• Keep the surface damp until the seedlings are up.
• Thin to the strongest seedling at each station.

Care by growth stage

Steady water decides how tender the leaves are, and a light, regular feed keeps new leaves coming. Weeks count from sowing.

Water at the base in the morning, so the leaves dry quickly and downy mildew has less chance. If growth stalls in poor soil, a light dose of all-purpose controlled release granular (NPK around 14-5-10) scratched into the soil can help.

Thinning

Final spacing depends on the variety, since 'Georgia Southern' grows much larger than 'Vates'.

• Snip unwanted seedlings at soil level rather than pulling them.
• Remove yellowing lower leaves at the stalk so air moves around the base.
• Bin leaves with downy mildew spots rather than composting them.
• Snap off flower stalks at the base as soon as they appear.
• Pull finished plants with their roots, so no stumps carry disease on.

Companion planting

Good neighbours for collards are plants from other families, which neither share its caterpillars nor carry clubroot.

Grows well with

• Dill, whose strong scent may help to confuse egg-laying cabbage white butterflies.
• Onion, which is not a brassica, so it shares none of the brassica pests or clubroot.
• Dwarf beans, which stay low and make a good crop to rotate with collards.

Keep apart

• Mustard, a host of cabbage aphid and clubroot.
• Tomato and climbing beans, whose tall growth shades and crowds low collard plants.

Harvesting Leaves

Start picking 8 to 11 weeks from sowing, once each plant has plenty of leaves. Take leaves before they reach full size, while they are still tender.

• Pick from the bottom up, taking the lowest, outer leaves first.
• Snap or cut each leaf at the base of its stalk.
• Leave the top rosette and the growing tip untouched, so the plant keeps cropping.
• Pick young leaves for stir-fries and mature leaves for steaming or braising.

Collards hold well on the plant, so pick only what the kitchen needs. Store picked leaves in a perforated plastic bag in the fridge, or chop, blanch and freeze them for longer keeping. Strip out the tough midrib of big leaves, then slice and steam them, stir-fry them or use whole leaves as wraps.

Common problems

Flower stalks in spring. Collards are biennial, so plants that have come through a cold season usually flower in spring. Their leaves then turn small and bitter, so sow again rather than wait.

Tough, coarse leaves. Leaves left to reach full size lose their tenderness, so pick them younger and keep the plant producing new ones.

Seedlings collapsing. Damping off rots the stem at soil level in wet mix, and brassica seedlings may stand on a thin, twisted stem called wire stem. Read more

Seedlings cut off at ground level. Cutworms feed at night and hide in the soil by day, so scratch the surface around the stump to find the curled caterpillar. Read more

Pests and diseases

Caterpillars do most of the damage to collards, and the best defence is looking under the leaves often. Use only sprays whose label names leafy brassicas, and keep to any withholding period.

Cabbage white butterfly (Pieris rapae). The white butterflies with dark wing spots lay eggs on the leaves, and velvety green caterpillars chew large holes and leave green droppings. First recorded in Melbourne in 1929, it is probably the most common butterfly in home gardens. Pick the caterpillars off, or spray a Bacillus thuringiensis (Bt) product. Read more

Diamondback moth (Plutella xylostella). Pale green caterpillars up to 10 mm long feed under the leaves, leaving papery windows that tear into holes, and wriggle hard when touched. In Queensland they resist several insecticide groups, so rely on Bt, hand picking and the small parasitic wasps that attack them. Around Stanthorpe, mid to late summer crops suffer more than early summer ones. Read more

Cabbage aphid (Brevicoryne brassicae). Grey-green aphids up to 3 mm long form dense colonies, coated in whitish powder, under the leaves and in the centre. Hose them off with a strong jet or spray insecticidal soap. Read more

Downy mildew (Hyaloperonospora parasitica). Yellow patches form on the upper leaf with greyish white growth beneath, most often on crowded seedlings in cool, moist weather. Space plants well, water in the morning and remove affected leaves. Read more

Clubroot (Plasmodiophora brassicae). Plants yellow, wilt and stall, and the roots are swollen and knobbly when dug. Pull affected plants with their roots and bin them, then lime and drain the bed and grow no brassicas there.

Prevention first

• Cover young plants with fine insect mesh so butterflies and moths cannot lay eggs.
• Check both sides of the leaves twice a week and crush any eggs.
• Pull wild radish, mustard weeds and shepherd's purse near the bed, which harbour brassica pests and diseases.
• Space plants as in Thinning, so air moves freely between them.

Tips

1. In frosty districts, time an autumn sowing so plants reach picking size around the first frosts. Count back 8 to 11 weeks from your usual first frost.
2. Sow a few more seeds than you need and keep the spare seedlings in their tray for a fortnight, to fill any gaps cutworms leave.
3. Collards cross with kale, cabbage, broccoli and cauliflower, which are the same species. For seed that comes true, let no other brassica of that species flower nearby.