How to Grow Astragalus in Australia

Astragalus (Astragalus mongholicus, long sold as A. membranaceus) is a hardy perennial of the pea family, Fabaceae, grown for its yellow taproot and flowers. Also called huang qi, it comes from sunny steppe and mountain slopes from Siberia to northern China, so it suits Australia's drier, frost-touched gardens. Most failures happen before the first leaf: the hard-coated seed rarely comes up unless the coat is broken first.

Three mistakes that matter

1. Sowing the seed as it comes. The seed coat keeps water out, so untreated seed can sit in damp soil for weeks without swelling, or never come up at all. Rub and soak every seed first, as Germinating the seed describes.
2. Planting into wet, heavy soil. Astragalus roots rot in soil that stays wet, and root rot is the main cause of losses where summers are warm and humid. Grow it in deep, free-draining soil or a raised bed, and water less once plants are established.
3. Moving it too late. The seedlings resent root disturbance, and a taproot damaged at transplanting often grows short and branched. Sow where the plant is to grow, or plant out from a deep tube while the seedling is still small.

When to plant

Treated seed germinates best in cool to mild conditions, roughly 10 to 20°C, and poorly at 30°C. Sow in autumn or spring, and keep trays out of summer heat. One sowing is enough, because each plant stays in the ground for two or three years.

In frosty districts, sow in spring once hard frosts have passed, so small seedlings are not caught by their first winter. Where summers turn hot and humid, sow in autumn so roots are down before the storms arrive.

Site, soil and setup

Wild astragalus grows in sunny grassland and thickets on dry mountain slopes, where snow falls in winter and the soil drains fast. Copy that in the garden: full sun, deep loose soil, and nothing that holds water around the crown.

Germinating the seed

Astragalus seed has physical dormancy (a seed coat that water cannot get through). The coat is built of tightly packed cell layers, so a dry seed can lie in moist soil without taking up water. Break or soften that coat and the seed swells within a day, then usually germinates in 3 to 10 days.

Treated fresh seed is not hard to raise. In a field trial in Alabama, soaked seed of the best line reached about 90 per cent emergence within a week. A Chinese study got about 88 per cent from seed that was warmed in water, rubbed and sown in sand. Old seed is another matter: one lot, probably stored too long, managed 4 per cent. Sow two or three seeds for each plant you want, and use the freshest seed you have.

Most gardeners need only the first row, with the third as a follow-up for stubborn seed. Our article on soaking, scarification and cold stratification explains why hard seed behaves this way.

When nothing comes up

• The seed never swelled. The coat was not broken, so nick and soak any hard seed before sowing again.
• It was sown too deep. Seedlings struggle up through deep soil, so sow again at the depth under Sowing Seeds.
• The tray was too hot. Germination falls away in heat, so move trays to a cool, bright spot or wait for autumn.
• The seed rotted. Fungi such as Fusarium rot swollen seed in cold, soggy mix, so use a free-draining seed raising mix and keep it just moist.
• The seed was old. Stored seed loses vigour, so buy or save fresh seed and keep it cool and dry until sowing.
• You gave up too soon. Treated seed sown cool, at about 13°C, can take 4 to 9 weeks or more. Wait at least 9 weeks before sowing that tray again.

Sowing Seeds

Start astragalus from treated seed, sown straight into the bed or into deep tubes that go out while the seedlings are small.

Sowing direct

• Sow two or three treated seeds together at 5 mm deep, and never deeper than 7 mm.
• Space each group 20 to 45 cm apart, in rows 30 to 45 cm apart.
• Keep the surface just moist until the seedlings are up.
• Thin each group to its strongest seedling once plants reach 10 to 15 cm, snipping the others at soil level.

Starting in tubes

• Sow one or two seeds in each deep tube or small individual pot of seed raising mix.
• Stand the tubes in a cool, bright spot out of hot afternoon sun.
• Harden off the seedlings (stand them outside for longer each day over about a week) before planting.
• Plant out as soon as they are large enough to handle, sliding the whole root ball into the hole.
• Seed raising mix can carry Legionella bacteria, so wet it down, wear gloves and a P2 mask, and wash your hands afterwards.

The hardening off article sets out a week of half days that suits these seedlings.

Care by growth stage

Steady water while the seedlings establish, then a drier routine, decides the crop more than feeding does. Feed sparingly: compost before sowing, one potassium feed in the third spring, and the light granular feed below only if growth stalls.

If growth stalls in very poor, sandy soil, a light application of all-purpose controlled release granular (NPK around 14-5-10) scratched into the soil can help. Like other legumes, astragalus can fix nitrogen, but only with the right root bacteria. One field trial found no nodules at all until the seed was treated with bacteria matched to Astragalus. Do not count on the plant feeding itself.

Cutting Back

In frosty districts the tops die each winter and the plant regrows from its crown in spring, so cutting back is mostly tidying.

• Cut frosted, blackened stems down to just above the crown in winter.
• Leave green stems standing through the growing season, since the leaves feed the root.
• Remove leaves badly marked with powdery mildew, and put them in the bin, not the compost.
• Cut out stems snapped by wind or chewed through by weevils; new shoots grow from the crown.

Companion planting

Astragalus is happiest beside other sun-loving plants that like lean, dry soil, and away from the legumes that share its pests.

Grows well with

• Thyme, which wants the same full sun and sharp drainage.
• Lavender, which also dislikes wet feet and rich feeding.
• Oregano, a low, dry-soil perennial that leaves room for the taller stems.

Keep apart

• Lucerne and clover, which host whitefringed weevil grubs and cowpea aphids.
• Beans, legumes that share the same weevil and aphid.
• Lettuce and other thirsty leafy crops, whose frequent watering keeps the soil too wet for astragalus roots.

Harvesting Roots

Lift the roots in autumn of the second or third year, once cooler weather or the first frost has turned the tops yellow and brown.

• Cut the dead tops back first so you can see the crown.
• Dig down beside the plant with a garden fork or spade to at least 30 cm, since a good taproot runs longer than that.
• Lever the soil away and ease the root out whole, rather than pulling on the crown.
• Shake off the soil and rinse the root in cold water.
• Leave one plant in the bed to flower and set seed for the next sowing.

Dry the roots whole in an airy place out of strong sun, or in gentle warmth below 50°C. In one Japanese trial, hot-air drying above 50°C changed what the dried roots contained. When they are fully dry, store them in an airtight jar in a cool, dark cupboard.

Traditional use and history

In traditional Chinese medicine, the dried root is known as huang qi. It has been used in China for more than 2,000 years, usually combined with other herbs. It was first recorded in the Shennong Ben Cao Jing, a classic herbal of the Han dynasty, which ranked it among its high-grade herbs. Centuries later, Li Shizhen's Compendium of Materia Medica, written in the Ming dynasty, listed huang qi first among the herbs it called tonics.

The Pharmacopoeia of the People's Republic of China records the herb as the dried root of Astragalus membranaceus and of its variety mongholicus. Botanists now treat the two as one species, Astragalus mongholicus. Beyond China, the root has a long history as a folk herb in Korea, Mongolia, Kazakhstan and Russia.

The plant was domesticated in northern China, Korea and Japan, where it is grown on a large scale. It has also been introduced to fields in Germany, Poland and Turkey. Chinese tradition regards roots from Shanxi province as di dao material. Overharvesting has made wild stands scarce, and the plant is listed as vulnerable on the Red List of Endangered Plants in China.

Safety

Happy Valley Seeds sells astragalus 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.

The store's seed carries no shipping restriction to any state. For weed rules in your area, check your state's biosecurity or primary industries department.

Common problems

Seedlings collapse at soil level. Damping off (a rot of very young seedlings caused by soil fungi and water moulds) strikes in cold, wet mix. Sow into free-draining mix and water only when the surface dries. Read more

The plant vanishes in winter. Frost kills the tops of astragalus, but the crown survives and sends up new shoots in spring, as Cutting Back describes.

Short, branched roots. A hard layer close under the topsoil stops the taproot going down, so it splits sideways. Loosen the next bed to the depth given in Site, soil and setup.

Pale, slow plants. Without the right root bacteria, no nitrogen-fixing nodules form, and the plant runs short of nitrogen. Look for pink-centred nodules on a lifted seedling, and give the light granular feed from Care by growth stage where none appear.

Pests and diseases

Astragalus shares its pests with lucerne and clover, and its diseases with any plant left in wet soil.

Whitefringed weevil (Naupactus leucoloma). Legless cream grubs feed on the roots, mostly of legumes, and can kill seedlings; the flightless grey-brown adults notch leaf edges. Naupactus grubs did serious damage to seedling roots in one astragalus trial, so pick adults off at night and rotate beds. Read more

Cowpea aphid (Aphis craccivora). Aphids are among the main pests of astragalus where it is farmed, and this shiny black aphid of legumes is common across Australia. Dense colonies gather on shoot tips, yellowing the leaf veins and twisting the stems. A firm jet of water or insecticidal soap knocks them back. Read more

Powdery mildew (Erysiphe species). A white powder spreads over the leaves in mild, humid weather. Remove the worst leaves, space plants for airflow and water at the base. Read more

Root and crown rot (Pythium, Phytophthora and Fusarium species). Plants wilt suddenly and the roots turn brown and soft, most often where soil stays wet in warm weather. Lift and bin affected plants, and fix the drainage before replanting.

Prevention first

• Drainage, sparing water and a bed away from other legumes, as Site, soil and setup describes, prevent most root rot and weevil trouble.
• Where weevil grubs have been bad, grow a cereal or grass there for a season before astragalus goes in.
• Dig an infested bed over in September or October, when the grubs are mature or pupating.
• Check shoot tips for aphids and leaf edges for weevil notches every week.

Tips

1. Push a stake in beside each plant, because the tops vanish in winter and a fork can find the crown by accident.
2. Plant it where you can watch the bees, which work the pale yellow pea flowers through summer.
3. Pick pods once they dry and turn papery, keep the seed cool and dry, and sow it in the next autumn or spring.
4. Sow a small second patch a year after the first, so one batch of roots comes ready each autumn.