How to Grow Silverbeet in Australia

Silverbeet (Beta vulgaris, Cicla group) is a biennial in the amaranth family, Amaranthaceae, grown for its broad leaves and thick white or coloured stems. Elsewhere it is Swiss chard or chard, and many Australians call it spinach. True spinach (Spinacia oleracea) is a different plant, while beetroot is the same species bred for its root. One sowing can be picked for months in every zone, and the usual mistake is leaving each clump of seedlings unthinned.

Three mistakes that matter

1. Leaving every seedling. Each corky seed is a cluster that sends up two to six seedlings, and a crowded clump stays small and spindly. Thin each clump to its strongest seedling, as set out in Thinning.
2. Letting plants go short of water or food. A stressed plant stops making large, tender leaves and runs to seed sooner (bolting, when a plant sends up a flower stem). Keep the soil moist and feed fortnightly, as in Care by growth stage.
3. Leaving seedlings unguarded. Snails and slugs go straight for young silverbeet, most of all on damp nights after rain. Start controls the week seedlings emerge, as in Pests and diseases, rather than after the first row disappears.

When to plant

Silverbeet seed germinates in soil between 10°C and 30°C, and soil above 35°C sends it dormant. Sow a short row every three to four months within your zone's window, so young plants take over as older ones slow down.

At the cold edge of a window, raise seed in trays under cover. Plant out after the last hard frost, since seedlings survive only a light frost. At the hot edge, sow into moist soil and shade seedlings through hot spells.

Site, soil and setup

Silverbeet grows in full sun or part shade, with at least four hours of sun a day. Its roots can run 90 to 120 cm deep, so dig the bed deeply and enrich it well.

Use only well-rotted or composted manure, because fresh manure can carry food-poisoning organisms onto leaves that may be eaten raw. For more on correcting acid soil, see soil pH explained.

Container growing

Silverbeet is one of the most reliable crops for a pot. Its long roots need a pot at least 30 cm across and holding 10 to 15 L, with good drainage holes. Fill it with premium potting mix and compost. Both 'Barese' and 'Magenta' suit pots well, since they are grown for young leaves and keep slender stems.

• Water: keep the mix evenly moist, checking daily in summer heat.
• Feed: fish and seaweed blend at 25 mL per 9 L, fortnightly.
• Position: full sun in the cooler months, light shade through summer.

Sowing Seeds

Sow silverbeet direct where it will grow, or raise it in trays for planting out; first pick the type that suits the job.

Choosing a type

'Silverton' seed comes coated with fungicide. Handle it with gloves, wash your hands afterwards and keep it away from children and animals; the plants it grows are safe to eat.

Sowing direct

• Sow 12 to 15 mm deep into moist soil, 30 cm apart, in rows 40 to 50 cm apart.
• Keep the surface moist; seedlings show in 5 to 14 days, slower in cool soil.
• Mulch with straw once seedlings stand clear of the soil.

Raising in trays

• Sow one cluster per cell of seed-raising mix, 12 to 15 mm deep.
• Plant out when seedlings are 5 to 10 cm tall, 30 cm apart.
• Harden off (accustom seedlings to sun and wind over about a week) before planting out.
• Water in well straight after planting.

Care by growth stage

Nitrogen and water decide how large and tender the leaves grow. Weeks count from sowing.

Silverbeet is not drought-resistant. A plant that wilts on a hot afternoon recovers once watered, but repeated wilting hastens bolting.

Thinning

Thin when seedlings stand about 5 cm high, before the clumps compete for light and water. Well-spaced plants grow larger leaves, and their leaves dry faster after rain.

• Snip extra seedlings at soil level with scissors, so the roots of the one you keep stay undisturbed.
• Leave one strong seedling every 30 cm for picking leaves, or every 20 cm for cutting whole plants.
• Eat the thinnings in salads, except those grown from treated seed.
• Pinch out flower stems as soon as they appear.
• Remove yellowing old leaves, which shade the plant and harbour disease.

Companion planting

Good neighbours share few of silverbeet's pests, or stand upright beside its broad leaves.

Grows well with

• Onions, garlic and chives, whose slim, upright leaves take little light or room.
• Cabbage and cauliflower, from a different family with mostly different pests.
• Tall tomatoes on the western side, which can give afternoon shade in summer.

Keep apart

• Beetroot and spinach, which host the same Cercospora leaf spot.
• Amaranth, a host of beet webworm and leaf spot.
• Squash, cucumber and melons, whose sprawling vines smother young plants.

Harvesting Leaves

Start picking 8 to 10 weeks after sowing, when the outer leaves reach about 30 cm long. Baby leaves can be taken from about 4 to 5 weeks.

• Pull each outer stem down and away at the base, or twist it off, rather than cutting it.
• Take the outer leaves first and leave the young centre to grow on.
• For a single harvest, cut the whole plant at its base.
• Check the backs of leaves for insects before washing.

Picked leaves wilt and decay quickly. Keep them in a sealed container in the coldest part of the fridge and use them within a week or so. Store them away from tomatoes and rockmelons, whose ethylene speeds decay.

Cook the leaves like spinach and the stems like celery, or eat young leaves raw in salads. Silverbeet is high in oxalates, so anyone prone to kidney stones is best to eat it sparingly, particularly raw.

Common problems

Running to seed in spring. Plants sown late in autumn grow slowly through winter and often bolt in spring; pick them hard and sow a fresh row. Stress makes it worse; see Three mistakes.

Cracked midribs and brown spots. Boron deficiency, most likely where soil pH sits above 6.8. Confirm it with a soil test, then apply a soluble trace element mix at label rate.

Smaller leaves and thicker stems. Normal on older plants after months of picking; a new sowing replaces them.

Frost-marked leaves. Hard frost and wet winter weather damage leaves on the tablelands; pick off marked leaves.

Pale, winding tunnels in leaves. Serpentine leafminer (Liriomyza huidobrensis) maggots feed inside the leaf, and the fly is now present in Queensland, New South Wales and Victoria. Pick off mined leaves, since sprays tend to fail, and report unusual or severe mining to the Exotic Plant Pest Hotline on 1800 084 881.

Stunted, yellowing plants that wilt. Knotted, swollen roots point to root-knot nematodes (Meloidogyne species), worst in warm, sandy soil. Grow a cereal or leave the bed fallow for a season before silverbeet goes back in. Read more

Pests and diseases

Insect pests seldom trouble silverbeet, and most leaf disease follows warm, humid weather.

Common garden snail (Cornu aspersum) and slugs. Introduced molluscs that chew seedlings and leaves, feeding at night and after rain. Collect them by torchlight and set beer traps among the seedlings. Read more

Beet webworm (Spoladea recurvalis). Green caterpillars up to 2 cm long, with a dark line along the back, graze leaf undersides and leave clear windows in the upper surface. Squash young caterpillars under the leaves.

Cercospora leaf spot (Cercospora beticola). Light grey spots with brown or reddish rims appear on older leaves, and their centres drop out to leave holes. It spreads in warm, wet weather and survives on seed, weeds and old leaves, so remove spotted leaves early.

Bacterial leaf spot (Pseudomonas syringae). Grey-centred spots with purple margins, easily mistaken for Cercospora; unlike Cercospora, no fungicide controls it. Avoid long spells of wet leaves and avoid bruising plants, since wounds let it in.

Downy mildew (Peronospora farinosa). In cool, damp weather, pale yellow patches appear on the leaves, young ones first, with a grey to violet down beneath. Space plants and water in the morning so leaves dry quickly. Read more

Damping off (Pythium species). Seed rots before it emerges, or seedlings collapse at soil level soon after, most often in wet soil. Avoid overwatering and thin early for airflow. Read more

Prevention first

• Water in the morning, so leaves dry before night.
• Pull fat hen, amaranth, pigweed and saltbush nearby, which host beet webworm and leaf spot.
• Clear out spent plants promptly, since leaf spot lives on in old leaves.
• Clear logs, rocks and leaf litter from bed edges, where snails shelter.

Tips

1. Plant coloured-stem types such as 'Ruby Red' or Rainbow among flowers, where they earn a place in a front bed.
2. When a plant starts to flower, cut it off near the base and it can resprout.
3. Seed can stay viable for up to four years stored cool and dry, so one packet covers several sowings.