How to Grow Turnips in Australia

Turnip (Brassica rapa) is a quick, cool-season member of the cabbage family, Brassicaceae, grown for its round roots and its young leaves. The small Japanese types are ready weeks before the globes. The roots are sweetest grown fast in cool weather and pulled small, and most disappointments come from heat, dry soil or roots left too long.

Three mistakes that matter

1. Sowing into the heat. Roots that swell in hot weather turn woody and strong-flavoured, and heat or dry soil pushes plants to bolt (flower and set seed early). Sow in the cooler months shown for your zone in When to plant.
2. Skipping the thinning. Crowded seedlings grow leaf at the expense of root, and the roots that do form stay small or misshapen. Thin early, to the spacing in Choosing a type, and keep thinning until the roots have room.
3. Letting the roots grow big. A turnip left to grow to tennis-ball size or beyond can turn woody, tough and bitter. Start pulling as soon as the first roots reach the size in Choosing a type, rather than lifting the whole row at once.

When to plant

Turnip seed germinates in soil from 12°C to 30°C, but the roots grow best in mild weather. Japanese types do best at about 15°C to 20°C. Heat makes roots woody, and a long cold spell below 10°C after a late autumn sowing can trigger bolting. Sow a short row every two to four weeks through your zone's window for a steady supply.

At the warm edge of a window, sow the quick Japanese types, which can be out of the ground before the heat builds. At the cold edge, finish sowing before the long cold spells of late autumn set in.

Site, soil and setup

Turnips need loose, fine soil and steady moisture more than rich feeding. Prepare the bed a month or more ahead so manure and lime have time to settle.

Hold back on nitrogen: too much grows lush tops and misshapen roots. Rotation matters because clubroot, in Pests and diseases, lives in the soil for years.

Container growing

The small Japanese types suit pots best, and 'Tokyo Cross F1' is bred for close spacing. Use a pot or trough at least 40 cm wide and 20 cm deep; a 40 cm round pot holds about 28 L. Fill it with premium potting mix blended with extra compost. 'Tokyo Market', 'Tokyo Cross F1' and 'Hida Beni F1' all make small roots that fit.

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

• Water: pots dry out fast, so check them daily in warm weather and water before the mix dries.
• Feed: fish and seaweed blend at 25 mL per 9 L, fortnightly from the first true leaves.
• Position: full sun in the cooler months; move the pot into afternoon shade on warm days.

Sowing Seeds

Sow turnip seed direct where it is to grow, because root crops do not transplant well.

Choosing a type

'White Egg' swells partly above the soil, so its size shows at a glance. Give 'Heirloom Mix' globe spacing, because it holds white, purple and golden globes together.

Sowing direct

• Sow about 10 mm deep in a shallow drill, scattering seed thinly, 2 to 3 cm apart.
• Space rows as in Choosing a type.
• Keep the surface moist with a fine spray until the seedlings show, usually in 5 to 10 days.

Some 'Golden Globe' and 'Japanese Sugukina' seed is treated with thiram, a fungicide, and the packet says so. Never eat treated seed, keep it away from children and animals, wear gloves to sow it, and wash your hands afterwards.

Care by growth stage

Even moisture from sowing to harvest decides the quality of the root. Weeks count from sowing, and Japanese types move through each stage faster.

Weed by hand close to the plants, because a hoe blade nicks the shoulders of the roots. A mulch of sugarcane, pea straw or lucerne between the rows holds moisture and keeps weeds down.

Thinning

Thinning gives each root room to swell, because crowded plants compete for water and light. Thin in two passes to the spacing in Choosing a type. Make the first when seedlings are big enough to handle, and the second about a fortnight after they come up.

• Pull the smaller, weaker seedlings and leave the strongest.
• Press the soil back around the seedlings that remain.
• Rinse the thinnings and eat them as salad greens, but only those grown from untreated seed.

Companion planting

Turnips grow fast enough to fill the gaps between slower crops.

Grows well with

• Peas, beans and beetroot, which are not brassicas, so the cabbage aphid and cabbage caterpillars pass them by.
• Lettuce and spinach, quick leaf crops that fit between turnip rows.
• Carrots and parsnips, whose slow rows the turnips share and then vacate.

Keep apart

• Cabbage, broccoli and radish, which carry the same caterpillars, aphids and clubroot.
• Mustard and kale, for the same reason, set out in Pests and diseases.

Harvesting Roots

Brush the soil from the top of a root to judge its size, and pull when it reaches the size in Choosing a type.

• Harvest in the cool of the morning and keep the roots cool, especially Japanese types.
• Loosen the soil beside the row with a fork, then pull by the base of the leaves.
• Twist or cut the tops off, leaving 1 to 2 cm of stalk on the crown.
• In cool weather, globe types can stay in the ground and be dug as needed, before they pass eating size.

Remove the leaves before storing, because they draw moisture from the root. Japanese turnips keep up to two weeks in the fridge. Globe roots keep for several weeks in trays of moist sand or coir in a cool, frost-free place.

Slice or grate young Japanese turnips raw into salads, and roast, steam or add older globes to soups, stews and casseroles.

Common problems

Flowering before the root swells. Plants bolt for the reasons in Three mistakes and When to plant, and bolted roots turn hard. Sow by the zone table and pull bolted plants.

Split roots. A soaking after a dry spell makes a swelling root crack open; keep watering even, as in Care by growth stage.

Big leaves, small or misshapen roots. Too much nitrogen, lumpy soil or crowding, as in Site, soil and setup and Three mistakes.

Brown patches inside the root. Boron deficiency causes brown discolouration on and inside the root, and moisture stress in hot, windy weather causes internal browning too. Keep the soil moist, and use a soluble trace element mix per label only where a soil test shows boron is short.

Gaps in the row. Seed sown too deep, a surface left to dry before the seedlings show, or snails grazing the seedlings. Read more

Pests and diseases

Turnips share their pests and diseases with cabbage and broccoli, although a quick crop escapes many of them.

Cabbage white butterfly (Pieris rapae) and diamondback moth (Plutella xylostella). Green caterpillars of both chew the leaves; diamondback caterpillars grow to about 10 mm and graze windows that tear into holes. Cover rows with fine insect mesh from sowing, and squash eggs and caterpillars under the leaves. Read more

Cabbage aphid (Brevicoryne brassicae). Dull grey-green aphids up to 3 mm, in colonies coated with a whitish powder under the leaves, which also spread turnip mosaic virus. Olive to grey-green turnip aphids and green peach aphids colonise turnips too; treat them the same way. Hose small colonies off, or spray insecticidal soap, following its label and any withholding period. Read more

White rust (Albugo candida). Smooth, shiny white blisters under the leaves burst into white powder, worst in cool weather with heavy dews. Remove affected leaves and bin crop debris after harvest.

Clubroot (Plasmodiophora brassicae). A soil-borne disease that swells and distorts the true roots and stunts plants, which wilt on warm days. It favours wet, acid soil. Bin infected plants with their soil, improve drainage, and lime acid soil towards pH 7.0 to 7.5. Clean soil off tools and boots before working another bed.

Black rot (Xanthomonas campestris). Yellow to light brown V-shaped patches spread in from the leaf edges, and the veins inside turn black. The bacteria spread in rain and water splash, fastest in warm, moist weather, and can carry on seed and brassica weeds.

Redlegged earth mite (Halotydeus destructor). Velvety black mites about 1 mm long with orange-red legs, active from autumn to spring in southern Australia. Their feeding silvers the leaves, and heavy numbers can kill seedlings as they emerge. Check new rows for the first five weeks, and pull broadleaf weeds such as capeweed nearby.

Prevention first

• Turn a few leaves each week for eggs, caterpillars and aphids, under mesh too, since aphids can build up inside it.
• Pull wild radish, wild turnip and other brassica weeds, which carry aphids, white rust and black rot.
• Water the soil in the morning so the leaves dry before night.
• Rotate brassica beds as in Site, soil and setup.

Tips

1. Eat the greens. Pick a few outer leaves from about four weeks, leaving four to six on each plant, and pick fewer if you want a good root. Young leaves go raw into salads; larger ones cook like spinach.
2. Grow 'Hida Beni F1' for colour. Its scarlet skin hides pink-streaked white flesh, crisp raw when young and good for cooking when left longer.
3. In Canberra and other cool gardens, a February to March sowing gives roots through winter, and light frost can sweeten Japanese types.