How to Grow Dang Shen in Australia

Dang shen (Codonopsis pilosula) is a twining perennial vine of the bellflower family, Campanulaceae, grown for its nodding green bells and its fleshy root. It is sold as Dang Shen seed. The step to get right comes first: the tiny seed germinates best in light, so it belongs on the surface, not under soil.

Three mistakes that matter

1. Burying the seed. The seed germinates best in light, so seed pushed under the mix often does nothing. Press it onto the surface, as Germinating the seed describes.
2. Leaving the root wet through winter. The dormant root rots easily in cold, soggy soil. Grow it in a free-draining bed, a mound or a pot, and water very little once the tops die down.
3. Losing the spring shoots to slugs and snails. Kew's growers found new shoots are often eaten before they have a chance. Protect every plant from the moment shoots appear, as Pests and diseases sets out.

When to plant

Sow when the seed raising mix holds about 18 to 25°C, which in most districts means early spring under cover. Fresh seed can come up at any time of year, but a spring sowing gives seedlings a full season before their first dormancy.

In frosty districts, raise seedlings under cover and plant out after the last frost. The dormant root is very hardy, but young spring shoots are frost-tender. Where winters are cold, a tray sown in late autumn and left outdoors lets winter supply the chill that older seed needs.

Site, soil and setup

Dang shen likes its roots cool and its head in the light, the way it grows through shrubs at a forest edge. In hot gardens, give it morning sun and afternoon shade: strong sun scorches the leaves, and the vine wilts fast on hot days.

Dig in a 5 cm layer of compost before planting. Where the ground stays wet after rain, build a mound or raised bed so winter water drains away from the root. Do not replant dang shen where it grew before: its roots release compounds that hold back its own seedlings and young plants.

Container growing

A pot keeps the root dry in winter, and Kew grows its plants in pots partly to keep slugs and snails away. Depth matters most, because the root spirals in a shallow pot. Use a pot at least 40 cm across and 32 cm deep, which holds about 28 L, for one plant. Use quality potting mix with about one part perlite to four parts mix.

• Water: lightly while shoots are young, deeply in full summer growth, and hardly at all once the tops die back.
• Feed: worm casting liquid diluted to weak tea colour, fortnightly from spring to midsummer.
• Position: morning sun and afternoon shade; move the pot under shelter in a wet winter.
• Support: a tripod of stakes about 1.5 m tall, or strings to a railing, set in at potting time.
• Saucer: remove it in winter, so the mix never sits wet.

Germinating the seed

Dang shen seed is small, about 1 mm long and red-brown to dark brown. Like many small seeds of the bellflower family it germinates best in light, so it is sown on the surface. Fresh seed needs no treatment: Kew's growers sow it on moist seed compost under a light covering of vermiculite, and seedlings appear within a month. Kew finds older seed comes up better after a short spell of cold, so chill seed that is not fresh. Chilling cannot revive dead seed, though, and Chinese growers find year-old seed often fails.

This is not a hard seed. Growers report seedlings in 7 to 21 days, and up to six weeks at 20°C. In two Chinese trials, about 80 to 90 per cent of seed germinated at 15 to 25°C, and fewer at 10°C. One found none at 5°C. Seed lots vary widely, so treat that as a best case. A 25-seed packet allows two or three seeds per plant wanted, with some left for a second sowing.

More on these methods is in Soaking, Scarification and Cold Stratification.

When nothing comes up

• Covered too deeply. Seed under soil stays in the dark; sow again on the surface and press it in.
• Too cold. Germination slows and falls in cool mix and stops near 5°C, so move the tray indoors or onto a seedling heat mat.
• Surface dried out. Surface-sown seed fails if the mix dries out, so keep the lid on and water from below.
• Old or warm-stored seed. Germination falls as seed ages, and year-old seed kept warm may not come up at all. Sow fresh seed, and keep packets sealed in the fridge.
• Stratification bag dried out or went mouldy. Start again with sand that holds together when squeezed but drips no water.
• Given up too soon. If nothing shows after three or four weeks in warmth, chill the tray in the fridge for two to four weeks, then warm it again. Leave an outdoor tray through winter, since late seed may still come up in spring.

Sowing Seeds

Start dang shen in deep cells under cover, because the seedlings are tiny and the long root resents being moved.

Starting under cover

• Fill deep cells or tubes with fine seed raising mix and water them first.
• Sow two or three seeds per cell, press them onto the surface, and leave them uncovered or barely dusted.
• Keep the cells at the warmth When to plant gives, in bright light out of direct sun, under a clear lid.
• Lift the lid once seedlings show, and keep watering from below.
• Snip off all but the strongest seedling in each cell, rather than pulling, to spare its root.

Mixing the seed with a little dry sand makes it easier to spread (see How to Sow Tiny Seeds).

Sowing direct

Sowing into fine, weed-free soil at the foot of the support is possible after the last frost, but it is a gamble. Seedlings this small dry out quickly and make an easy meal for slugs.

Transplanting

Plant out after the last frost, once seedlings are about 10 cm tall. First harden them off (get them used to outdoor sun and wind over about a week), as hardening off seedlings describes. Set each plant about 40 cm from the next, at the foot of its support, at the depth it grew in the cell. Slide the root ball out whole, water it in with seaweed solution at half strength, and put slug protection in place the same day.

Care by growth stage

Water decides this crop: plenty while the vine is in full growth, then a nearly dry root through winter. Feed lightly, since the aim is a sound root rather than a mass of leaves.

If growth stalls in poor soil, a light application of all-purpose controlled release granular (NPK around 14-5-10) scratched into the soil in spring can help.

New shoots climb fast, twining around anything nearby. Guide them onto the support every few days in spring, before they tangle with their neighbours.

Cutting Back

Dang shen needs little cutting: the vine dies back to the root every autumn and regrows in spring.

• Clear the dead stems at ground level once the tops have died back completely.
• Mark each crown with a labelled stake, so the dormant plant is not dug up or weeded out.
• Divide only with care, teasing small pieces from the side of the clump while it is dormant; see Dividing Perennials.

Companion planting

Pair dang shen with plants that shade its roots without smothering it.

Grows well with

• A light, open shrub it can twine through, as it does at a forest edge.
• Chives, whose low, slim clumps shade the root zone without climbing into the vine.
• Sorrel, which suits the same moist soil and part shade.

Keep apart

• Mint, whose runners crowd a young plant and compete for the same moist soil.
• Comfrey, whose big leaves smother a slow-starting seedling.
• Lavender, which wants hot, dry, lean ground that would starve dang shen of summer water.

Harvesting Roots

Lift the roots in the second or third autumn, once the tops have died down completely and the plant is dormant.

• Choose plants at least two, and better three, seasons old.
• Clear the dead stems and loosen the soil with a garden fork, working well out from the crown.
• Ease the root out whole, since it can run 15 to 30 cm deep and snaps easily.
• Cut off a piece of crown carrying buds and replant it for a later harvest.
• Wash and scrub off the soil, then slice the root.
• Dry the slices on a rack at about 40°C for 12 to 18 hours.

The dried root is rich in sugars, so it draws insects and mould in storage. Store the slices in airtight, labelled jars in a cool, dark cupboard. Before anyone thinks of using the root, read Safety.

Traditional use and history

The Chinese name, dang shen, is a shortened form of Shangdang dang shen. Shangdang was a commandery (an administrative district) under the Qin dynasty, in present-day Shanxi province. When the district was renamed Luzhou under the Tang dynasty, the root became Lu dang shen, a name still in use. Historical herbals placed the finest roots in the hills around Pingshun, Huguan and Lingchuan, near the city of Changzhi.

Its place in Chinese tradition

Dang shen was first used in place of ginseng, and English-speaking sellers know it as poor man's ginseng. The Qing dynasty scholar Wu Yiluo gave it an entry in his Ben Cao Cong Xin, writing that roots from Shangdang were the best. In the terms of traditional Chinese medicine, the dried root was classed as tonifying the middle qi and was linked with the spleen and lungs. The Chinese Pharmacopoeia has listed it since the second half of the twentieth century. It accepts the roots of this species, its variety modesta and the close relative Codonopsis tangshen under one name.

Collectors and growers

Adrien Franchet described the species from a specimen Père David collected in the hills near Beijing, where David reported it was cultivated for medicine. Augustine Henry, collecting its close relative in Hubei, found the root traded around Ichang as a substitute for ginseng, though rated below it. Wild stands have grown scarce, so cultivated roots make up most of the trade. Farmers in Wenxian in Gansu and Pingshun in Shanxi developed their own traditional way of drying the root, known as rubbing and sweating. China lists the dang shen growing system around Changzhi among its Important Agricultural Heritage Systems.

Safety

Dang shen is sold as seed for growing, and nothing here is advice to eat or take any part of the plant. Anyone thinking of using a plant should first seek advice from a qualified health practitioner.

Common problems

Root rots over winter. Cold, wet soil around the dormant root is the usual cause, so move survivors to a mound or pot. Read more

Leaves scorch and the vine wilts by afternoon. Hot sun and dry soil stress a plant of forest edges, so water deeply, mulch, and give it afternoon shade.

Spindly, pale seedlings. Too little light after germination stretches the stems, so move the tray to bright light at once. Read more

No flowers in the first year. Plants often wait until their second summer to flower, though an early spring sowing may flower by late summer, so give it time.

Pests and diseases

Kew's growers find disease is rarely a concern in cultivation; the damage growers report comes from animals that eat the shoots or the sweet root.

Garden snail (Cornu aspersum). Snails, and slugs with them, feed at night and can eat new spring shoots to the ground. Hand-pick them after dark, set beer traps, ring pots with copper strips, or scatter iron-based snail pellets thinly at the label rate. Read more

Aphids (Aphididae). Small green or yellow sap-suckers cluster on soft tips, leaving malformed new growth and sticky honeydew. Knock them off with a strong jet of water, or spray insecticidal soap at the label rate on the undersides of leaves. Read more

Two-spotted mite (Tetranychus urticae). Tiny mites feed under the leaves in hot, dry weather, leaving pale speckles and fine webbing. Keep the plant well watered in dry spells, and spare the predatory mites and small black ladybirds that eat them. Read more

Damping off (Pythium species and Rhizoctonia solani). Seedlings rot before they emerge or collapse at soil level soon after. Use fresh mix and clean trays, avoid overwatering, and thin crowded seedlings. Read more

House mouse (Mus musculus). Mice and rats dig for the sweet root. Grow the plant in a pot or a wire-lined raised bed. Trap only once you are sure the digger is not a protected native animal, using covered snap traps checked daily rather than poison baits. Read more

Prevention first

• Check for snails and slugs after dark from the moment spring shoots appear.
• Line a bed with wire mesh, or grow in pots, where mice are about.
• Water deeply in hot, dry spells, so mites and wilting do not take hold.
• Start seed in clean trays of fresh mix, and water from below.

Tips

1. Label every stratification bag with the date it went into the fridge.
2. Sow a few plants in successive springs, so one is ready to lift each autumn and the rest keep growing.
3. Collect seed from ripe seed heads in autumn, dry it thoroughly, and store it in a sealed jar in the fridge.