How to Grow Peanuts in Australia

Peanut (Arachis hypogaea) is a frost-tender annual legume in the pea family, Fabaceae, grown for the nuts that form underground. Australia's peanut industry is centred on Kingaroy in Queensland's South Burnett, yet a warm backyard bed can grow a crop wherever summers run long. Flowers bloom above ground and push stalks called pegs into the soil, so most failures start with soil too hard or dry.

Three mistakes that matter

1. Sowing into cold soil. Seed sitting in cool, damp ground is slow to emerge, and soil fungi often rot it before it breaks through. Wait for the soil temperature given in When to plant, and sow into moist, not wet, soil.
2. Choosing hard or heavy ground. Pegs cannot push into compacted clay, and pods that do form tear off when the plant is lifted. Grow in loose, sandy soil, and keep mulch 10 cm back from the stems so pegs can reach the surface.
3. Letting the bed dry out after flowering. Dry topsoil stops calcium reaching the pods, leaving empty shells, and lets in moulds that produce aflatoxin, a toxin that makes kernels unsafe to eat. Water steadily from first flowers through to digging, as Care by growth stage sets out.

When to plant

Sow once the soil 5 cm down holds at least 18°C at 9 am, after the last frost; seed germinates best between 20 and 35°C. The crop needs 16 to 24 weeks of warm weather from sowing to digging, so most gardens get one sowing a year.

At the early edge of a window, wait until the soil has held that warmth for three mornings running and no heavy rain is forecast. At the late edge, count forward 16 to 24 weeks to check the crop can be dug before autumn frost or tropical downpours.

Site, soil and setup

Like other legumes, peanuts host root bacteria that fix nitrogen from the air, which is why they need so little feeding. Leave at least a year before peanuts return to the same bed, because leaf spot survives in old plant remains.

Sowing Seeds

Sow raw, unroasted kernels with the papery skin intact, such as 'Big Pink', straight into the bed where they will grow.

Sowing direct

• Handle seed gently, like eggs: a split kernel or torn skin will not germinate.
• Sow 3 to 5 cm deep, 15 to 20 cm apart, in rows 60 to 75 cm apart. Go shallower in heavy or wet soil, since deep seed rots more often.
• Sow into moist soil and water in once. Unless the surface dries out, hold off until shoots appear, usually in 7 to 14 days.
• Where peanuts have never grown, a peanut inoculant (Group P rhizobia) at sowing helps roots form nitrogen-fixing nodules; follow its label.
• Sow a few spare seeds in pots to fill gaps, because some seedlings are usually lost as they emerge.

Seed peanuts are for sowing, not eating. Seed can carry a fungicide dressing, so wear gloves, wash your hands afterwards and store leftover seed well away from children and the pantry.

Starting in pots in cool areas

• In short seasons, sow one seed per small pot of seed raising mix, kept warm and sheltered, a few weeks before the soil outside warms.
• Plant out after the last frost, when seedlings are about 10 cm tall, at the spacing above.
• Harden off (get seedlings used to sun and wind outdoors) over about a week first.

Care by growth stage

Steady moisture and calcium in the topsoil decide the crop, because each pod draws its calcium straight from the soil around it. Weeks count from sowing and stretch in cool weather.

When plants reach about 30 cm and pegs start to dangle, draw a little loose soil or compost under the spreading branches. Keep it off the crown. Pegs longer than about 7 cm seldom reach the soil unaided. Pull weeds by hand rather than hoeing among the pegs.

Skip potash-rich fruiting feeds, because heavy potassium can block the calcium that pods need. If you prefer a conventional feed, choose a low-nitrogen blend with phosphorus, potassium, sulphur and trace elements. Fork in about 30 g per square metre a few weeks before sowing.

Companion planting

Peanuts are legumes like beans and peas, which have their own guides. They sit well under tall crops and badly beside plants that share their soil diseases.

Grows well with

• Corn, with the low peanut plants beneath acting as a living mulch that keeps the soil cool and moist.
• Lettuce and silverbeet sown after the harvest, which use the nitrogen that peanut roots leave behind.

Keep apart

• Tomato, capsicum and beans, which share white mould, a soil fungus that also rots peanut stems and pods.

Harvesting Pods

Most crops are ready 16 to 24 weeks after sowing, once the leaves start to yellow and the inside of most shells has darkened.

• As leaves yellow, lift one plant and open a few pods from the centre of the bush, which ripen first.
• Dig when most shells are dark brown inside and the kernels have their full skin colour; pale, white-lined shells need longer.
• Water the day before if the soil is dry, so pods stay on their pegs as you lift.
• Lift whole plants with a garden fork and shake off loose soil.
• Sift the loosened soil for pods that broke away.
• Do not wait much past ripeness: within a week or two, pegs weaken and pods drop off in the ground.

Curing

Start drying the same day you dig, because damp pods left in a heap invite mould.

Before eating or storing, throw out any kernel that is mouldy, shrivelled or discoloured. Aflatoxin moulds are not always visible, which is why steady watering and prompt drying matter. Eat peanuts raw, roasted or salted, or toss them through salads and stir-fries.

Common problems

Gaps in the row. Split or skinned seed does not germinate, and seed sown too deep or too early often rots; see Three mistakes and Sowing Seeds.

A big, leafy bush with few pods. Long spells above 30°C push growth into leaves, and pegs that dangle too high never reach the soil; see Care by growth stage.

Empty shells. Pods with no kernel, called pops, come from too little calcium where pods form. They are worst in dry seasons or after heavy potash, and gypsum at first flowers prevents them.

Pods left behind at digging. Pegs weaken when plants stand past ripeness or lose leaves to leaf spot, and pods snap off in dry, hard soil.

Pests and diseases

A home crop seldom needs spraying, because peanuts tolerate a good deal of leaf loss. If you do spray, choose a product whose label covers peanuts.

Native budworm (Helicoverpa punctigera). Its caterpillars chew leaves and growing tips from emergence to pegging. Its look-alike, cotton bollworm (Helicoverpa armigera), tends to damage flowers and pegs, and both are managed the same way. Check plants twice a week while they flower and pick caterpillars off by hand.

Lucerne seed web moth (Etiella behrii). In dry years its larvae slip down through cracked soil, bore into pods and eat the kernels. Damaged pods carry far more aflatoxin than sound ones. Keep the surface soil moist late in the season, and dig promptly once the crop is ready.

Early and late leaf spot (Passalora arachidicola and Passalora personata). Round brown to black spots up to 10 mm across appear on the lower leaves first, often ringed in yellow, and leaves drop early. The fungi survive in old peanut plants, so bin spotted tops rather than composting them.

Peanut rust (Puccinia arachidis). Orange-brown pustules full of powdery spores form under the leaves, which then yellow, dry and wither. It is common in peanut districts north of Kingaroy. The fungus lives only on living peanut plants, so pull out every self-sown peanut between crops.

White mould (Athelia rolfsii). A branch or whole plant wilts suddenly, with thick white fungal threads and pinhead-sized white to brown balls at soil level. It lives in most soils and attacks many vegetables. Avoid wounding stems or heaping soil on the crown, and bin affected plants.

Prevention first

• Rotate beds as Site, soil and setup describes, and pull out self-sown peanuts, which carry leaf spot and rust between crops.
• Water the soil, not the leaves, early in the day: leaf spot infects only when leaves stay wet for about 10 hours.
• Check under the lower leaves at least once a week from flowering, when spots and caterpillars first show.
• Bin or bury the tops of diseased plants, and compost only healthy ones.

Tips

1. For a clearer read on ripeness, scrape the outer skin off a few pods with a pocket knife. The curved saddle of the pod turns dark brown to black when the kernel is mature.
2. Keep the plumpest pods from healthy, well-watered plants as next year's seed, stored in the shell and shelled only on sowing day. Peanuts pollinate themselves, so different varieties can grow side by side.
3. Dig healthy spent tops back into the bed or add them to the compost, returning nitrogen and organic matter for the next crop.