How to Grow Burdock in Australia

Burdock (Arctium lappa) is a member of the daisy family, Asteraceae, grown as an annual for its long, slender taproot, the gobo of Japanese cooking. It is a biennial, so it only flowers and sets seed in its second year. It grows from Darwin's dry season to a Hobart summer. Western Australian farms have grown it on the sandy Swan Coastal Plain for export to Japan. Most failures come from the soil, not the plant: a root that meets hard or lumpy ground forks, bends or stops short.

Three mistakes that matter

1. Sowing into shallow or compacted soil. Forking often starts in the top 15 cm, where the soil was not dug well enough. Dig the bed about 50 cm deep and pick out stones, or build a deep raised bed, as set out in Site, soil and setup.
2. Feeding too hard. Heavy fertiliser, especially nitrogen, grows big leaves and can fork the root, most of all when it sits in a band below the seed. Rely on compost dug through the whole bed and the light feeds in Care by growth stage.
3. Leaving roots in too long. Past their best, roots turn pithy and woody, and a plant left into its second year sends up a flower stalk and spreads hooked burrs. Start digging at 16 to 20 weeks, and cut any flower stalk that appears.

When to plant

Soil temperature decides the start: sow once the soil holds at least 10°C, and 10°C to 20°C suits germination best. In temperate and subtropical gardens it is a spring and autumn crop. Where winters are cold it suits spring and summer, and in the tropics the dry season.

On hot, sandy ground, sow on a flat bed: in Western Australian trials, hilled beds dried out and fewer seeds came up. Where winters are cold, frost blackens the leaves but spares the root; dig it before new growth starts in spring.

Site, soil and setup

The root is the crop, so the bed matters more than anything above ground. Dig it a month ahead, and dig it deeper than you would for carrots.

On shallow or clay ground, a tall raised bed or a deep timber box filled with loose soil does the job instead. Japanese growers build boxes on top of the soil for the same reason. Sandy soil suits the root but holds little water, so work in extra compost and mulch well.

Sowing Seeds

Sow burdock direct where it is to grow, because the taproot is easily damaged when a seedling is moved.

The variety

Our burdock is 'Takinogawa Long', a traditional, late-maturing Japanese gobo with brown skin, white flesh and roots that can reach 1 m in loose soil. It is one of the varieties Western Australian researchers trialled. Its length is the reason the bed needs digging so deep.

Sowing direct

• Sow 5 to 10 mm deep in a shallow drill, with rows about 60 cm apart.
• Drop a seed every 5 cm or so, then thin as described in Thinning.
• Keep the surface evenly moist with a gentle spray until the seedlings are up.
• Expect seedlings in about 6 to 17 days.

Care by growth stage

A deep bed and steady moisture decide the root; burdock needs little feeding after that. Weeks count from sowing, and cool weather stretches every stage.

If growth stalls in poor soil, a light dose of all-purpose controlled release granular (NPK around 14-5-10) scratched in beside the row can help. Keep it off the seed line, for the forking reason in Three mistakes.

Weed by hand and hoe, because young burdock is slow to establish. The first eight weeks matter most, while seedlings are small and exposed.

Thinning

Thin early so each root has room to fill out. Keep the spacing fairly close, though: dense rows encourage long, straight roots, while crowded ones stay thin.

• Thin to a final 10 to 20 cm once the seedlings are big enough to handle.
• Cook the thinnings, leaves and tiny root together, as a green vegetable.
• Pick a few young leaves from some plants for the kitchen, and leave the rest untouched to size their roots.

Companion planting

Burdock grows tall and leafy and roots deep, so it pairs best with shallow-rooted crops.

Grows well with

• Beans and peas, shallow-rooted crops that do not compete for deep soil.
• Mustard, Tagetes marigolds or oats, grown and dug in before sowing to help keep nematodes down.

Keep apart

• Carrots, parsnips and potatoes, which compete for the same deep soil.
• Low crops that need full sun, which burdock's broad leaves can shade out.

Harvesting Roots

Start digging from about 16 weeks, while the root is crisp and before any flower stalk appears. A root 2 to 3 cm across at the top is a good size, and leaves dying back are another sign. Young roots can be lifted from about two months, while autumn sowings grow slowly through winter and can take up to about eight months.

• Dig one test root first to judge size.
• Loosen the soil down the side of the root with a fork or spade, to its full depth.
• Ease the root out gently: it is long and brittle and snaps easily. Treat it as a careful dig, not a quick pull.
• Leave the soil on until you are ready to cook.

Scrubbing breaks the thin skin and dries the flesh, so store roots unwashed, wrapped in a plastic bag in the coldest part of the fridge. Near 0°C they can keep three to five weeks. At 12°C, roots in a Western Australian trial began to sprout after 11 days.

Peel young roots and eat them raw or pickled. Slice older roots into soups, stews, stir-fries or the Japanese dish kinpira, after a short soak in cold water to mellow the earthy edge. Young leaves, slightly bitter, go into salads or are cooked like spinach.

Common problems

Forked or bent roots. Shallow digging, stones or rich feeding, as set out in Three mistakes. Dig the next bed deeper.

Short, thick roots. High nitrogen makes roots shorter and thicker at the top, while leaner soil grows them longer. Feed as in Care by growth stage.

Patchy or no germination. Soil too cold, a surface left to dry, or seed on a hot, dry mound. Read more

Roots rotting in wet ground. Warm weather and waterlogged soil favour root rots such as black root. Improve drainage, or grow in a raised bed, and rotate beds.

Pests and diseases

Few pests bother burdock, but these four turn up in Australian gardens and trials.

Snails and slugs (Gastropoda). They chew the stems and leaves, and seedlings suffer most. Pick them off, or protect seedlings with snail bait used as the label directs. Read more

Root-knot nematode (Meloidogyne species). Microscopic worms that raise lumpy galls on the roots, so plants wilt and yellow even in moist soil. Remove affected plants and seal them in a bag in the sun, then treat the bed as in Site, soil and setup before sowing again. Read more

Powdery mildew (Erysiphe and related fungi). White powdery patches on the leaves in humid weather, which the crop usually tolerates without losing its root. If it spreads, spray 1 part full-cream milk to 10 parts water. Read more

Damping off (Pythium species). A soil-borne rot that decays seed before it emerges and collapses seedlings at soil level. It struck a trial near Perth sown in warm March weather. Sow into free-draining soil and avoid keeping it soggy. Read more

Prevention first

• Check seedlings often for snails and slugs.
• Rotate beds each year, so soil pests and rots do not build up.
• Water deeply and less often, so the soil never stays waterlogged.
• Water at the base of the plants, keeping the leaves dry.

Tips

1. Sow a little thicker than the final spacing, because burdock seed can come up unevenly.
2. Choose a row you can reach from both sides, so you can dig down beside each root at harvest.
3. A young flower stalk, cut before the buds open, is edible. Peeled and cooked, it tastes a little like artichoke.
4. Burdock has naturalised in Victoria, New South Wales and Queensland, mostly in moist, disturbed ground. Dig out any self-sown seedlings near the garden while they are small.