How to Grow Potatoes in Australia

Potato (Solanum tuberosum) is a member of the nightshade family, Solanaceae, grown for its tubers (swollen underground stems packed with starch). A home patch can grow waxy, floury and coloured varieties rarely seen at the greengrocer. The mistake most gardeners make is planting potatoes from the kitchen. Sweet potato and Jerusalem artichoke are different plants with guides of their own, and potato onions are shallots.

Three mistakes that matter

1. Planting shop potatoes. Potatoes bought to eat can carry viruses such as potato virus Y and soil diseases that persist in the bed. Plant seed potatoes grown for planting.
2. Planting into cold, wet soil. Seed tubers sitting in cold, soggy ground often rot before they shoot, and frost blackens early shoots. Wait for the cue in When to plant, and plant into free-draining soil.
3. Following tomatoes or potatoes. Blights, potato tuber moth and scab carry over in soil used by the nightshade family. Choose a bed where no potato, tomato, capsicum, chilli or eggplant has grown for three or four years.

When to plant

Plant once the soil holds about 10°C and the risk of frost has passed. Potatoes grow best in mild weather and need cool nights, so in warm zones plant for the cooler months, not the summer heat. Where the window is long, a second planting a few months later extends the harvest.

At the cold end of a window, chit the seed potatoes first so the crop gets away quickly. Hilling and Mounding covers frost protection. At the warm end, choose an early variety so the crop is dug before the heat arrives.

Site, soil and setup

Go easy on lime, wood ash and heavy doses of manure, because a less acid or heavily manured soil encourages common scab. For testing and adjusting soil, see soil pH explained.

Container growing

A free-draining 50 to 85 L pot, grow bag or sack, at least 40 cm wide and deep, holds two or three seed potatoes. Sit the seed potatoes on 10 cm of premium potting mix blended half and half with compost, and cover them with 10 cm more. Determinate varieties (which grow to a set height) suit pots best: try 'Kipfler', 'Nadine' or 'Avanti'.

• Watering: never let the mix dry out; shallow early layers dry quickly in sun and wind.
• Feeding: blood and bone at planting, about 15 g for a 40 cm pot. Then fish and seaweed blend at 25 mL per 9 L, fortnightly.
• Position: full sun, out of strong wind.
• Topping up: add potting mix and compost as the shoots grow, until the container is full.
• Safety: potting mix can carry Legionella bacteria, so wet it, wear gloves and a mask, and wash your hands after.

Planting Seed Tubers

Potatoes grow from seed potatoes (small whole tubers kept for planting), not from seed. Due to quarantine restrictions and our shipping policy, we cannot send seed potatoes to Western Australia, Tasmania or Kangaroo Island.

Choosing seed potatoes

Chitting

Chitting (sprouting seed potatoes before planting) gives the crop a head start. Set the tubers eyes up in an egg carton, sprouting on the windowsill or anywhere bright but out of direct sun. After two to four weeks they carry short, sturdy shoots about 1 cm long. The full method is in how to chit seed potatoes.

Planting out

• Plant egg-sized seed potatoes whole. Cut larger ones into pieces with at least one eye each, and let the cuts dry for a day or two first.
• Dig a trench about 20 cm deep and set the tubers in it, shoots up.
• Cover them with 10 to 15 cm of soil.
• Space them 25 to 40 cm apart, in rows 50 to 75 cm apart.
• Water in with seaweed solution (see Care by growth stage), then water only when the soil dries.
• Expect shoots in about three weeks.

On hard or clay ground, set the seed potatoes 30 cm apart on loosened soil instead. Cover them with 20 to 30 cm of straw. The tubers form in the straw, which is topped up as the plants grow.

Care by growth stage

Even moisture while the tubers form, and potassium from flowering, make a clean crop. Weeks count from planting and shift with variety and climate.

Potatoes are not heavy drinkers, and overwatering in poorly drained soil invites pests. A straw mulch keeps the soil evenly moist.

Hilling and Mounding

Hilling (drawing soil, compost or straw up around the stems) keeps light off the tubers and shelters young shoots from frost. How much hilling a plant needs depends on whether the variety is determinate or indeterminate.

• Start when the shoots reach about 20 to 30 cm.
• Draw soil, compost or straw up the stems, leaving the top 10 cm of leaves showing.
• Repeat every few weeks until the ridge stands 20 to 30 cm high.
• Cover any tuber that pushes through to the light.
• If frost is forecast, bury young shoots completely under soil or straw.

Companion planting

Keep potatoes away from their own family, which shares their pests and diseases, and give them room in full sun.

Grows well with

• Peas, a legume outside the nightshade family that carries none of the potato blights.
• Cabbage and other brassicas, a rotation crop that helps a scab-affected bed recover.
• Sweet corn, a grass that makes a good rotation crop where scab has shown up.

Keep apart

• Tomato, which shares late blight, target spot and potato tuber moth.
• Eggplant and capsicum, hosts of the same blights and of tuber moth.
• Pumpkin, another food plant of the 28-spotted ladybird.
• Sunflower, which shades a potato bed from its tall stems.

Harvesting Tubers

Dig the main crop once the tops yellow and die back, usually 12 to 20 weeks after planting. Once plants flower, you can bandicoot a few new potatoes from the side.

• Rub a tuber with your thumb: if the skin slips off, leave the crop a few more days.
• Dig on a dry day, pushing the fork in well out from the stems.
• Lift the plant and sift the soil by hand for every tuber.
• Cook any speared or bruised tubers the same day, since they do not store.

Curing

Store only sound tubers with the soil left on, and check them often for rot. Early varieties are best eaten soon after digging, while late ones keep longest. Cook each type as Choosing seed potatoes describes.

Common problems

Green tubers. Light reaching tubers near the surface, or in storage, turns the skin green and toxic; hill them over, as Hilling and Mounding describes.

Seed potatoes rot without shooting. Cold, soggy soil or cut pieces planted before they dried usually cause it; see Three mistakes that matter.

Knobbly, cracked or hollow tubers. A dry spell followed by heavy watering makes tubers grow in fits and starts; keep moisture even, as Care by growth stage describes.

Poor tubers in hot weather. Heat as the crop matures spoils tuber quality, so time planting to finish before summer, as When to plant describes.

Plants wilt in moist soil. Wilting that water does not fix, with brown rings or ooze in cut tubers, points to bacterial wilt (Ralstonia solanacearum), worst in warm soil. Bag the plants and grow no nightshades there for over five years.

Green fruit on the plant. Some varieties set berries after flowering; they do the crop no harm but are poisonous to eat.

Pests and diseases

The six insects and diseases below cause much of the trouble in Australian potato beds, most starting in soil, seed or weeds.

Potato tuber moth (Phthorimaea operculella). Its caterpillars mine the leaves and tunnel into tubers through cracks in dry soil, and the larvae shelter among stored tubers and sacks. Keep the tubers deeply hilled, water to close soil cracks, and dig promptly once the tops die.

28-spotted ladybird (Epilachna vigintioctopunctata). This hairy, orange, leaf-eating ladybird and its spiny yellow larvae strip the leaf surface. Hand-pick adults and larvae when first seen, and clear nightshade weeds nearby.

Aphids, including green peach aphid (Myzus persicae). They do little direct harm but spread potato virus Y and other viruses between plants. Let hoverfly larvae, lacewings and ladybirds feed on them, and clear the weeds that shelter them. Read more

Target spot (Alternaria solani). Also called early blight, it makes dark leaf spots with rings like a target, usually late in the season. Keep plants fed and watered, and clear the dead tops after harvest.

Late blight (Phytophthora infestans). In mild, humid weather, grey-green patches turn brown and can collapse a crop within days. Pull out and bag infected plants at once, and never compost them. In Western Australia, report a suspected case to DPIRD.

Common scab (Streptomyces scabiei). This soil bacterium leaves rough, corky patches on the skin; scabby potatoes are still good to eat once peeled. Keep the soil moist while tubers form, and see Site, soil and setup on lime and manure. Powdery scab (Spongospora subterranea) looks alike but favours cold, wet soil: improve drainage.

Prevention first

• Water the soil, not the leaves, since wet foliage encourages blight and other fungal diseases.
• In Victoria and Western Australia, check leaf undersides for tomato potato psyllid (Bactericera cockerelli), which yellows, curls and stunts plants. Fine insect mesh keeps it off.
• Pull up volunteer potatoes that sprout from missed tubers, since they carry blight and virus over.
• Keep nightshade weeds, such as black nightshade, out of and around the bed.

Tips

1. Buy fresh seed potatoes each season rather than replanting your own, since viruses build up from crop to crop.
2. Never leave culled or rotten potatoes lying on the bed or path, because tuber moth breeds freely in them.
3. Where the garden soil is poor or has grown tomatoes, plant into a bin with its base knocked out, filled with compost and soil. At harvest, tip it over and spread the soil on a new bed.