How to Grow Jerusalem Artichokes in Australia

Jerusalem artichoke (Helianthus tuberosus) is a perennial sunflower (family Asteraceae) that stands 2 to 3 m tall and is grown for its knobbly, nutty tubers. Despite the name, it is only a distant relative of globe artichoke, and it is a different plant from yacon, potato and sweet potato. Most Australian gardens grow it with little fuss; the usual mistake is planting it where it can spread, since pieces left behind usually regrow.

Three mistakes that matter

1. Planting it in the main vegie patch. Knobs missed at digging time usually shoot again, and a clump can take over a bed and prove hard to clear. Give it a permanent, contained bed, as Site, soil and setup describes.
2. Feeding for leaf. High-nitrogen fertiliser grows towering tops at the expense of the tubers. Build the bed with compost, go gently on nitrogen, and feed potassium from flowering, as Care by growth stage sets out.
3. Digging too early. Tubers begin to swell only as the days shorten in late summer, and most of their growth comes in autumn. Hold off until the signs that Harvesting Tubers describes.

When to plant

Tubers sprout best once the soil holds about 8 to 15°C, and frost damages the young shoots badly, so plant as the last frosts end. One planting usually lasts for years. Where it does not persist, as in warm, humid districts, replant from stored tubers each year.

A tuber dropped back into each hole at digging time saves a spring planting.

Site, soil and setup

Because it stays put for years, it sits outside any crop rotation. Avoid a bed where sclerotinia rot (Sclerotinia sclerotiorum) has struck beans, lettuce or sunflowers, since the fungus survives in the soil.

Planting Tubers

Jerusalem artichoke grows from tubers, planted whole or cut into pieces. Due to quarantine restrictions and our shipping policy, we cannot send Jerusalem artichoke tubers to Western Australia or Tasmania. Plant tubers soon after they arrive; if the bed is not ready, store them as Harvesting Tubers describes.

Chitting

Chitting (sprouting tubers before they go in the ground) is optional and helps most in cool districts, where the soil warms late. Choose firm tubers about the size of a hen's egg, with no blackened or soft patches. Cut large ones into pieces with two or three eyes (buds) each, and let the cut faces dry for a day. Set them in a tray of barely damp potting mix in a bright, frost-free spot until short shoots show, much as for chitting seed potatoes.

Planting out

• Harden off chitted tubers with long shoots (accustom them to outdoor sun and wind) over about a week first.
• Plant tubers or pieces about 10 cm deep.
• Space them 25 to 30 cm apart, in rows 70 cm to 1 m apart.
• Water in with seaweed solution at 30 mL per 9 L, then mulch well.
• Keep the soil just moist, not wet, until shoots appear, often within one to two weeks and longer in cold soil.

Care by growth stage

Steady water and potassium while the tubers form decide the crop. Weeks count from a spring planting; in the tropics, the stages run through the dry season.

When the stems reach about 30 cm, draw soil up around them to about 15 cm high to steady the clump. In windy spots, pinch out the tips at about 1 m for a bushier plant, or stake around the outside of the block. Keep the mulch topped up, so tubers near the surface stay covered.

If you prefer a conventional feed, mix a controlled release all-purpose granular (NPK 12-3-8 to 14-5-10) into the bed at planting, at the label rate. In leafy growth, an all-purpose soluble (NPK 23-4-18 to 27-5-9) at half the label rate, fortnightly, is plenty. From the first flower buds, switch to a fruiting and flowering soluble (NPK 15-4-26 to 15-5-20) at the label rate, fortnightly.

Companion planting

Height, wandering tubers and shared diseases decide what belongs beside a stand.

Grows well with

• Cucumber, grown on the sheltered side, where the stand breaks hot, drying summer wind.
• Tomato, planted clear of the stand's shade but within its shelter from wind.

Keep apart

• Yacon, because replanted Jerusalem artichoke tubers may carry diseases over from year to year.
• Sunflower, a close relative that shares powdery mildew and sclerotinia rot.
• Potato, which also suffers sclerotinia rot, and whose bed stray tubers can invade.
• Low crops such as carrots and lettuce, which sit in deep shade on the stand's southern side.

Harvesting Tubers

Dig 4 to 6 weeks after flowering in warm districts, or once the tops die back where winters are cold. Either way, tubers usually need at least five months in the ground.

• Cut the stems down, leaving short stumps to mark each clump.
• Loosen the soil with a fork from outside the clump, since the thin skins bruise easily.
• Lift the clump, then feel through the hole for tubers that have broken away.
• Set aside a few firm, smooth tubers to replant, and dig out every other piece where you want the bed cleared.

Tubers keep best in the ground, so in cool, well-drained beds dig them as needed through winter; frost is said to sweeten them. In subtropical gardens and wet soils, lift the whole crop once the tops die, because tubers left in warm, wet ground can rot. Out of the ground they shrivel quickly. Keep them in a perforated bag in the fridge for 2 to 3 weeks, or in slightly damp sand or sawdust somewhere cool and dark.

Scrub rather than peel, then roast, boil or bake them, or grate very fresh tubers raw into salads.

Common problems

Tubers never shoot. Cold, soggy soil rots planted tubers, and tubers kept long out of the ground dry out first; plant firm, fresh tubers into free-draining soil.

Tall plants, few tubers. Rich nitrogen feeding or deep shade sends growth into stems and leaves; see Three mistakes that matter.

Small, knobbly tubers. Dry spells while tubers form in late summer and autumn keep them small and knobbly; water as Care by growth stage sets out.

Stems blown flat. Tall stems laden with flowers snap or topple in strong wind, and rocking loosens the tubers. Mound, pinch or stake as Care by growth stage describes.

Tubers rot in the ground. Waterlogged soil, or warm, wet ground after the tops die, rots the tubers; see Site, soil and setup and Harvesting Tubers. Read more

Tubers shrivel after digging. The thin skins lose moisture fast, and moulds attack tubers kept long out of the soil; store them as Harvesting Tubers describes.

Pests and diseases

Few pests trouble Jerusalem artichoke, and the odd caterpillar chewing its leaves rarely matters; these five are the ones to watch.

Garden snail (Cornu aspersum) and slugs. This introduced snail is widespread in Australian gardens. Snails and slugs graze the new shoots in spring and can hole tubers near the surface. Pick them off at dusk or after rain. Read more

Two-spotted mite (Tetranychus urticae). These tiny sap-suckers leave yellow stippling on the leaves, and numbers climb quickly in hot, dry weather. Hose the undersides of the leaves, and avoid broad-spectrum sprays, which kill the ladybirds and predatory mites that keep them down. Read more

Powdery mildew (Golovinomyces species). White, powdery patches spread over the leaves in humid weather where air is still. At the first spots, spray 1 part full-cream milk to 10 parts water. Read more

Sclerotinia rot (Sclerotinia sclerotiorum). This fungus rots stems at the base under a white, fluffy mould, then forms hard black resting bodies (sclerotia). These survive in soil for many years, so lift affected plants and their tubers promptly.

Fusarium wilt (Fusarium species). Disease is rare in this crop, but fusarium can ruin a large share of the tubers. Blackened areas on a tuber can signal it, so never replant such a tuber. Read more

Prevention first

• After sclerotinia rot, start a new clump from clean tubers in another bed.
• Leave room between plants and thin crowded clumps, so air moves through the leaves.
• Water the soil rather than the leaves.
• Bin, never compost, any diseased stems or tubers.

Tips

1. Keep peelings and small offcuts out of the compost heap, where they sprout and spread.
2. While the plants are still growing, dig carefully at the edge of the clump for the largest tubers, and leave the rest to fill out.
3. Slice tubers into water with a little lemon juice or vinegar, because the cut flesh browns.