How to Grow Swedes in Australia

Swede (Brassica napus var. napobrassica) is a member of the cabbage family, Brassicaceae. It is grown for its round, yellow-fleshed root, which is really the swollen base of the stem. It is also called rutabaga, and it is a separate crop from turnip, which matures sooner and usually has white flesh. Swedes shrug off frost and keep for months, so they give a steady winter vegetable from Perth to Canberra. The usual mistake is sowing too late, so the roots swell into warming spring days and turn hard instead of sweet.

Three mistakes that matter

1. Sowing at the wrong end of the season. A late sowing meets a long cold spell, or spring warmth and longer days. The plant then bolts (sends up a flower stem early), leaving a hard root. Sow in late summer and autumn, in your zone's window in When to plant.
2. Leaving seedlings crowded. Swedes sown thickly and never thinned compete for water and light, and the roots come up small and misshapen. Thin to 15 to 20 cm while the seedlings are young, as set out in Thinning.
3. Letting the soil dry out. A dry spell checks growth, and the roots can split, turn bitter or brown inside. Water deeply each week, mulch the rows, and keep the moisture even right up to harvest, as in Care by growth stage.

When to plant

Sow when the soil sits between 7°C and 25°C, and time it so the roots swell through cool weather. Above 25°C fewer seeds come up, and warmth at harvest makes the roots woody. For a longer harvest, sow a short row every few weeks through your window.

At the warm edge of a window, sow into moist soil and keep the row damp until the seedlings are up. At the cold edge, sow early enough for plants to establish first, because a long spell below 10°C can make young swedes bolt.

Site, soil and setup

Swedes want an open, sunny bed with deep soil that holds moisture yet drains freely. Start the preparation a month or more ahead, so lime and manure have time to settle.

Acid soil below pH 5.5 slows growth and favours clubroot, so test before you sow. Go easy on nitrogen, too: an excess pushes lush tops and misshapen roots.

Container growing

A swede grown to full size needs more root room than most pots give, so a pot suits a crop of small, young roots. Use a pot at least 40 cm across and 30 cm deep, which holds about 28 L. Fill it with premium potting mix and a few handfuls of compost. In a pot, lift our swede, 'Champion Purple Top', while the roots are small.

Potting mix can carry Legionella bacteria. Wet it first, wear gloves and a face mask to handle it, and wash your hands afterwards.

• Spacing: thin to 8 to 10 cm apart for baby roots.
• Water: pots dry out fast, and dry mix makes roots split or turn bitter, so check daily in warm weather.
• Feed: fish and seaweed blend at 25 mL per 9 L, fortnightly from the first true leaves.
• Position: full sun through the cool months.

Sowing Seeds

Sow swedes direct where they are to grow, because the young taproot does not like being moved.

Sowing direct

• Sow 10 to 15 mm deep, about 5 cm apart, in rows 30 to 50 cm apart.
• Keep the surface moist with a fine spray; seedlings usually show in 4 to 10 days.
• Mulch along the rows with straw once the seedlings are up.
• Thin as described in Thinning.

Starting in cells

Where the bed is not ready, sow into cells and plant out while the seedlings are small, before the main taproot forms. Harden them off first (a week of gradually longer spells outdoors, so they adjust to sun and wind). Then plant out 15 to 20 cm apart without breaking the root ball.

Care by growth stage

Even moisture and steady, unhurried growth decide the root. Aim for about 25 mm of water a week from rain and hose together. Weeks count from sowing, and cold weather stretches every stage.

As they mature, the roots push partly out of the soil, and frost does them no harm.

Thinning

Thinning is the one cut a swede crop needs, and it decides the size of every root. Do it once the seedlings stand about 5 cm tall.

• Thin to one plant every 15 to 20 cm along the row.
• Snip the spare seedlings off at soil level with scissors, rather than pulling them, to spare the roots left behind.
• Thin to 8 to 10 cm instead in pots, or for a row of baby swedes.
• Cook the young leaves of the thinnings like cabbage.
• Weed by hand close to the plants, because a hoe can nick the tops of the roots.

Companion planting

Good neighbours for swedes come from outside the cabbage family, so they share none of its caterpillars or clubroot.

Grows well with

• Peas and beans, legumes that share no cabbage-family pests, and a good crop to follow in rotation.
• Chives, a slim, upright plant that fits between the rows.

Keep apart

• Cabbage, broccoli, kale and turnips, which share clubroot, cabbage white caterpillars and aphids.

Harvesting Roots

Start lifting once a root reaches tennis-ball size, about 7 to 10 cm across, and finish before spring warmth makes it woody.

• Loosen the soil beside the root with a garden fork, then lift it.
• Twist off the leaves, leaving about 2 cm of stem so the root does not rot in storage.
• Brush off the soil, but leave roots for storing unwashed.
• Let 'Champion Purple Top' grow on to 10 to 15 cm across if you want larger roots.
• In cold gardens, leave roots in the ground and lift them as needed through winter.

Store roots in a cool, dark place with good air movement, where they can keep for four to six months in ideal conditions. Check stored roots often, and use any soft ones first.

Boil, steam, roast or mash the roots, or add them to soups, stews and casseroles.

Common problems

Small, forked or misshapen roots. Crowding causes most of them, as in Three mistakes, and too much nitrogen adds lush tops at the root's expense.

Brown flesh inside the root. Brown patches in and on the root point to a shortage of boron, called brown heart. Correct a diagnosed shortage with a soluble trace element mix at the label rate.

A flower stem and a hard root. The plant bolted after a long cold spell in late autumn or as spring warmed. Pull it, and sow in your zone's window next time.

Patchy or no germination. Soil hotter than 25°C, seed sown too deep, or a surface left to dry out. Read more

Pests and diseases

The cabbage family's usual troubles find swedes too, and caterpillars and aphids peak in autumn and spring.

Cabbage white butterfly (Pieris rapae). The white butterflies lay tiny eggs under the leaves, and the green caterpillars chew irregular holes and leave droppings behind. Cover young plants with fine insect mesh and pick off eggs and caterpillars. For heavier attacks, spray Bt (Bacillus thuringiensis, a caterpillar-only bacterial spray) following its label. Read more

Diamondback moth (Plutella xylostella). Pale yellowish-green caterpillars up to 10 mm long feed under the leaves, making small holes and clear windows, and wriggle hard when disturbed. Mesh and Bt control them as they do cabbage white. Read more

Cabbage aphid (Brevicoryne brassicae). Dull grey-green aphids form blue-grey colonies coated in whitish powder under the leaves, and their sap feeding yellows and distorts the growth. Hose small colonies off, or spray insecticidal soap following its label. Read more

Snails and slugs (Gastropoda). They feed after dark, can chew seedlings down to the ground, and are worst in the cooler months. Pick them off by torchlight, or scatter iron-based pellets. Read more

Clubroot (Plasmodiophora brassicae). A soil-borne disease that swells and distorts the fine roots, so plants stunt, yellow and wilt in warm weather. Bin affected plants rather than composting them, lime the bed, improve drainage, and keep cabbage-family crops off it for at least four years.

Prevention first

• Turn a few leaves each week to find eggs, caterpillars and aphid colonies early.
• Pull wild radish, wild turnip and other cabbage-family weeds, which carry aphids and diamondback moth.
• Rotate beds as in Site, soil and setup, and clean tools after working a clubroot bed.
• Avoid heavy nitrogen feeds, because soft, sappy growth draws sap-sucking insects.

Tips

1. In frosty gardens, wait for a few frosts before the main lift, because the cold turns starch to sugar and sweetens the roots.
2. Lift a few roots at about 5 cm across as tender baby swedes, which gives the rest more room.
3. Freeze a glut: peel and chop the roots, then blanch them before freezing.