How to Grow Mugwort in Australia

Mugwort (Artemisia vulgaris, family Asteraceae) is a tall, aromatic perennial grown for its deeply cut leaves, green above and silvery white beneath. The store sells common mugwort seeds and Japanese mugwort, or yomogi (Artemisia princeps), an East Asian species with downy, finely cut leaves. Both spread by rhizomes (creeping underground stems that send up new shoots) and self-sow, so they need a contained spot. The step most growers get wrong is burying the dust-fine seed, which needs light to germinate.

Three mistakes that matter

1. Burying the seed. Mugwort seed is as fine as dust and germinates in light, so a sprinkle of mix over the top can leave the tray empty. Sow it on the surface and firm it in, following Germinating the seed.
2. Planting it loose in a garden bed. Both species spread by rhizomes, and a piece of root left in the soil can grow into a new plant. Grow mugwort in a large pot or behind a sunken barrier, well away from the vegie patch.
3. Letting it set seed. Plants left to flower drop fine seed across the garden, and the wind-borne pollen can set off hay fever. Cut the flowering stems before the seed ripens, as Cutting Back and Containing explains.

When to plant

Mugwort seed germinates best with the mix at about 20 to 26°C and daylight reaching the surface. Sow in spring once nights stay mild, or in early autumn in warm districts. Warm days and cool nights help too, so a sheltered tray outdoors suits it. One sowing usually lasts for years, because the plants are perennial and spread on their own.

Early in a window, give trays extra warmth on a sunny sill indoors or a seedling heat mat. Late in a window, set trays in bright shade and wait for cooler weather before planting out.

Site, soil and setup

Mugwort tolerates poor, dry and rocky ground. Its real enemy is soil that stays wet, and its real risk is spreading where it is not wanted.

Container growing

A pot is the surest way to stop mugwort spreading, and both species grow well in one. One plant needs a pot of at least 30 L and 40 cm across, filled with a premium potting mix. Potting mix can carry Legionella bacteria, so wet it first, wear gloves and a mask, and wash your hands afterwards. Tall common mugwort needs a heavy pot in a windy spot, and a pot on paving keeps roots from escaping through the drainage holes.

• Watering: soak the pot once the top 3 to 5 cm of mix feels dry, then empty any saucer beneath it.
• Feeding: a fish and seaweed blend at half strength, about 12 mL per 9 L, fortnightly from spring to late summer.
• Position: a sunny spot, or one with shade after midday where summers are hot and pots dry quickly.
• Renewal: divide and repot the clump every year or two, once roots fill the pot.

Germinating the seed

Mugwort seed has no tough coat for water to get past. What it needs is light, moisture and warmth. Freshly harvested seed can hold a light dormancy that fades with dry storage or a spell of cold. In laboratory work at the University of Manchester, fresh common mugwort seed germinated best with light and alternating temperatures together, and it responded to chilling.

In germination tests recorded by the Seed Information Database, common mugwort gave 81 to 100 per cent at 20 to 26°C in daily light. No home-tray rate is recorded for common mugwort; the store's yomogi listing gives about 50 per cent. The seed is tiny, about 0.16 g per thousand for common mugwort and 0.07 g for yomogi. Sow a pinch of five or six seeds for each plant you want, and thin to the strongest.

Seed this fine is easier to spread evenly mixed with dry sand; sowing tiny seeds shows the method.

When nothing comes up

• Covered over. A layer of mix keeps the light out. Resow on top of the mix and firm it down.
• Flooded or parched. A can of water scatters fine seed, and sun dries the surface. Mist, or water from below, and lay clear plastic over the tray until leaves appear.
• Too cold. The recorded tests ran at 20°C and warmer. Move a tray off a cold winter sill onto a warm, bright one or a heat mat.
• Fresh, dormant seed. Seed straight off the plant may sit tight. Store it cool and dry for a few months before sowing, since dry-stored seed germinates faster.
• Tired seed. Kept cool and dry, seed stays good for several years; in open storage it lost about a quarter of its viability in four.
• Impatience. Allow six weeks of moist, bright conditions before starting again, since the recorded tests ran six to nine weeks.

Sowing Seeds

Trays give the most even stand, and a large pot or a contained bed can be sown directly. Whichever you choose, start with treated or untreated seed on the surface, as Germinating the seed sets out.

Starting in trays

• Moisten a punnet or cell tray of new seed raising mix and level it gently.
• Drop a small pinch into each cell, firm it down and leave it uncovered.
• Keep the tray bright but out of harsh afternoon sun, with the surface damp.
• When true leaves appear, snip out all but the best seedling in each cell.
• Pot each one on into its own small pot 3 to 4 weeks after sowing.

Sowing direct

Sow direct only into a large pot or a bed with a sunken barrier. Level the surface with a rake, dampen it, sprinkle the seed sparingly and press it on with the flat of the rake. Mist it each day until seedlings appear, then thin them to 60 cm apart at about 10 cm tall.

Planting out

• Move seedlings to the garden 6 to 8 weeks after sowing, at about 10 cm tall.
• Harden them off first (a week of gradually longer spells outdoors, so they toughen to sun and wind).
• Set them 60 cm apart at their pot depth, and settle them in with half-strength seaweed solution.
• Rig temporary shade for the first few days if a hot, drying wind is due.

The step from pot to bed is covered in hardening off seedlings before planting out.

Care by growth stage

Mugwort does best on little: sharp drainage, occasional water and hardly any feed. Over-feeding reduces the essential oils that give mugwort its aroma, so any feed goes on at half strength or less.

Where soil is very poor and plants stay small, one light feed is enough. Use all-purpose controlled release granular (NPK around 14-5-10), worked into the surface in spring.

Cutting Back and Containing

Gardening Australia's advice for Artemisia is one hard cut a year, when a plant opens up to show its inner branching. Gloves and long sleeves are worth wearing for all of it; Safety gives the reason.

• Remove flowering stems before their seed ripens, so the plant cannot sow itself about.
• Cut the whole clump to a few centimetres above the ground in late autumn or winter, once the tops brown.
• Pinch or shear the shoot tips in spring for a bushier clump with more leaves.
• Slice off runners that cross the barrier or the pot rim, and lift any shoots outside it.
• Put rhizome pieces in the rubbish bin, not the compost, since any piece can root.
• Split an ageing clump in late winter or early spring and replant the young outer pieces.

The method for splitting a clump is in dividing perennials.

Companion planting

Good neighbours for mugwort want the same sun and dry soil, and are sturdy enough not to be swamped by it.

Grows well with

• Yarrow, content in the same lean, sunny ground, with flowers that bring in aphid-eating insects.
• Lavender, a tough, sun-loving shrub that needs the same sharp drainage.
• Rosemary, which is woody enough to stand its ground in a dry, sunny bed.

Keep apart

• Vegetable seed beds, which the rhizomes invade; in laboratory tests, mugwort extracts also slowed the germination of other seeds.
• Mint, another spreader, whose liking for moist soil does not suit mugwort's dry bed.
• Tarragon, a smaller Artemisia relative that a mugwort clump soon crowds out.

Harvesting Leaves

Pick young shoots and leaves from spring, while the growth is soft and before the flower stems form. For drying, cut leafy stems as the first flower buds show.

• Pick mid-morning, after the dew has gone, wearing gloves.
• Leave at least two-thirds of each plant standing at every picking.
• Take whole stems, cutting with secateurs just above a pair of leaves.
• Tie stems in small bunches and hang them head down in a shaded, airy room.
• They are ready when the leaves crumble between the fingers and the stems break with a snap.

Keep the dried leaves in an airtight jar, away from light and heat, with the botanical name and the date of picking on the label. Dried stems keep their scent in wreaths and dried arrangements. The leaves and flowering tops contain thujone, so read Safety before any other use.

Traditional use and history

The genus is named for Artemis, the Greek goddess, and mugwort comes from the Old English mugcwyrt. One reading gives it as midge wort, from an old word for a small fly. Mrs Grieve's A Modern Herbal offered two more: the drinking mug, and an old word for a moth. In medieval Europe the plant was called mater herbarum, the mother of herbs.

Common mugwort is native to temperate Europe, Asia and North Africa, and yomogi to China, Korea and Japan. In Victoria, plants long recorded as common mugwort proved to be Chinese wormwood (Artemisia verlotiorum). That relative is naturalised in Victoria, New South Wales, Queensland and the ACT. Mugwort is also not wormwood (Artemisia absinthium), a separate plant with its own guide.

Safety

Happy Valley Seeds sells mugwort seed for growing. Nothing here is advice to eat or take any part of the plant. Before using any plant, talk first to a qualified health practitioner.

Ring 000 at once for collapse, a seizure, trouble breathing or a severe allergic reaction. For any other suspected poisoning, ring the Poisons Information Centre on 13 11 26, even before symptoms show.

Common problems

Empty trays. The seed was most likely covered or let dry; Germinating the seed and When nothing comes up give the fixes.

Thin, leaning seedlings. Weak light makes them stretch. Give the tray the brightest spot you have and turn it each day. Read more

Plants that rot over winter. Root rot sets in when soil stays too moist. Raise the bed or move pots out of the rain, and water less in cold weather.

Mugwort coming up everywhere. Rhizomes and self-sown seedlings spread it; see Three mistakes that matter and Cutting Back and Containing.

Plants that sulk in humid summer heat. Common mugwort comes from cool temperate regions and can struggle through long, hot, wet summers. In the tropics, grow it through the dry season in a pot with sharp drainage.

Pests and diseases

Mugwort's fragrant leaves deter many insects, and most trouble comes from sap-suckers in dry heat or from wet soil around seedlings.

Aphids (family Aphididae). Colonies of small, soft-bodied insects gather on new shoots, leaving sticky honeydew that turns black with sooty mould. Rub small colonies off with your fingers, blast them with the hose, or use insecticidal soap by the label. Read more

Two-spotted mite (Tetranychus urticae). Fine yellow flecks and mottling spread across the leaves, worst on the undersides, and the mites multiply in hot, dry spells. Hose or mist beneath the leaves, keep plants from drying out, and skip broad-spectrum sprays, which kill the mites' natural predators. Read more

Common garden snail (Cornu aspersum) and grey field slug (Deroceras reticulatum). On damp nights they chew young seedlings down. Collect them by torchlight, or scatter an iron-based snail bait thinly as the label directs. A dog that eats a large amount of any snail bait can be poisoned, so keep pets away from the bait and its packet. Read more

Damping off (Pythium species and Rhizoctonia solani). Young stems rot through at the mix surface and the seedlings topple, usually where the mix is kept too wet. Start with new seed raising mix in washed trays, and water lightly. Read more

Prevention first

• Raise trays under cover, out of rain and hose splash.
• Water at the base of plants, and hold back in cool, damp weather.
• Turn a few leaves and look at the shoot tips once a week from spring to autumn.
• Take away the boards, pots and leaf litter where snails hide by day.

Tips

1. To save seed, tie a paper bag over one or two ripening flower stems so the fine seed cannot scatter. Store it cool and dry. Some plants set little viable seed, so test a pinch on damp paper before relying on it.
2. Pot up a rooted runner in spring to give away, rather than sowing a second tray.
3. Keep yomogi and common mugwort in separate, labelled pots, so the two species stay distinct.