How to Grow Tansy in Australia

Tansy (Tanacetum vulgare, family Asteraceae) is a hardy daisy-family perennial grown for its ferny, strongly scented leaves and flat clusters of yellow button flowers. The store sells tansy seeds of the common species, which grows to about 1.2 m tall. It suits cottage gardens, herb borders and insect plantings from Hobart to the NSW Central Tablelands. The thing most gardeners get wrong is room: it spreads by creeping underground stems and self-seeds, so plan how to hold it before you sow.

Three mistakes that matter

1. Burying the seed. Tansy seed is tiny and comes up best from the top of the soil, so seed pushed deep into a tray often sits there. Cover it with no more than 2 mm of fine mix, as Germinating the seed explains.
2. Planting it loose in a bed. Creeping underground stems and dropped seed let one plant claim a border within a few seasons. Grow it in a large pot or behind a sunken barrier, and cut the flowers before seed ripens.
3. Treating it as a kitchen herb. The leaves and flowers are poisonous if eaten. Plant it away from herbs you pick for the kitchen, and read Safety before handling it.

When to plant

Sow when the seed raising mix sits between about 18 and 24°C; seedlings usually show in 2 to 4 weeks. Seed bank tests at Kew germinated tansy at every temperature from 11 to 26°C, so cooler trays still work. In most zones that points to late winter and spring, with a second window in autumn.

At the cold edge of a window, start trays on a heat mat or a warm windowsill. At the hot edge, give seedlings afternoon shade until they settle.

Site, soil and setup

Tansy grows wild on roadsides, fence lines and creek banks, and it takes almost any garden soil. Rich, moist soil makes it tall and quick to spread, while poorer, drier ground keeps it more compact.

Container growing

A pot is the easiest way to keep tansy in its place. Give one plant a pot of at least 30 L and 40 cm across, filled with a premium potting mix. Choose a heavy pot, since 1.2 m stems in flower catch the wind.

• Watering: water when the top 3 cm of mix is dry, and let the pot drain freely.
• Feeding: a fish and seaweed blend at half strength, about 12 mL per 9 L, fortnightly in spring and summer, only if leaves turn pale.
• Position: full sun, with afternoon shade where summers are hot, and never on bare soil where stems can root through the drainage holes.
• Renewal: lift and divide the clump every two or three years, when roots fill the pot.

Germinating the seed

Tansy seed has no deep dormancy, and well-stored seed usually comes up readily. In seed bank tests at the Royal Botanic Gardens, Kew, untreated seed gave 60 to 100 per cent in daily light, from 11 to 26°C. One lot reached 100 per cent within 14 days at 16°C. The seed is tiny, 1.2 to 1.8 mm long and roughly 6,000 to the gram, and it germinates best at or just under the surface.

Cold can matter for some lots. In Canadian trials, seed taken straight off the plant gave only 10 to 20 per cent without a chill. Seed that had spent a winter outdoors gave 70 per cent, rising to 90 per cent after more cold. A Montana lot gave about 75 per cent after a month of cold, damp storage. Sow three or four seeds for each plant you want, and chill any lot that is slow to start.

For handling seed this small, see how to sow tiny seeds without losing them, and for chilling in general, soaking, scarification and cold stratification.

When nothing comes up

• Sown too deep. Seed under a thick layer of mix often stays put. Sow again with only a dusting of cover.
• Dried out. Shallow seed dries fast. Cover the tray with clear plastic or glass until the first leaves show.
• Freshly saved seed. Seed straight off the plant is often dormant. Give it the fridge chill in the treatment table.
• Old or warm-stored seed. Kept at room temperature, seed loses about half its viability in 2 years. Store it cool, dry and sealed.
• Given up too soon. Keep the tray moist for six weeks before resowing, and chill the second batch first.

Sowing Seeds

Start tansy in trays for an even stand, or scatter it thinly where it will grow inside its pot or barrier. Both routes begin with shallow sowing, as Germinating the seed explains.

Starting in trays

• Fill a punnet or cell tray with fresh seed raising mix, firm it lightly and water it well.
• Scatter three or four seeds per cell and barely cover them.
• Stand the tray in bright, indirect light and keep the surface just moist with a mister.
• Thin each cell to the strongest seedling once the first ferny true leaves appear.
• Start trays 6 to 8 weeks before you plan to plant out.

Sowing direct

Rake the soil inside the pot or barrier fine and level, and water it. Mix the seed with a little dry sand, scatter it thinly and rake it in lightly. Mist daily until seedlings show, then thin to one plant per pot or 60 cm apart.

Planting out

• Plant out when seedlings stand 5 to 8 cm tall with several true leaves.
• Harden off first (stand the pots outdoors a little longer each day for a week, so they adjust to sun and wind).
• Plant at the same depth as in the pot, and water in with seaweed solution at half strength.
• Water twice a week until new growth shows, then weekly in dry spells.

More on the move from tray to garden is in hardening off seedlings before planting out.

Care by growth stage

Containment decides more than feeding does. Over-feeding reduces the essential oils that give tansy its scent and pushes soft, floppy growth, so feed at half strength at most.

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

Cutting Back and Containing

Two habits spread tansy: seed dropped from ripe flower heads and pieces of creeping underground stem (rhizome). Wear gloves, as Safety explains.

• Cut flower stems as the yellow buttons fade and brown, before seed ripens.
• Never slash or mow plants in seed, which scatters it, and brush seed off clothing and pets after working near them.
• Dig out shoots that appear beyond the pot or barrier, lifting every piece of rhizome.
• Bin seed heads and rhizomes rather than composting or dumping them, and keep plantings away from creeks, dams and drains, since the seed floats.
• Cut all stems to 10 cm in late autumn or winter, once they brown off.
• Lift and divide clumps in spring or autumn every few years, replanting young outer pieces.

Division renews a tired clump: see dividing perennials.

Companion planting

Choose neighbours that share its sun and can hold their own, and keep low plants out of reach of its roots.

Grows well with

• Yarrow, another tough daisy-family plant whose flat flower heads draw the same lady beetles.
• Echinacea, a tall perennial that stands up to a vigorous neighbour.
• Cosmos, an annual that fills gaps around a potted clump and feeds the same insects.

Keep apart

• Thyme and other low herbs, which its creeping stems overrun.
• Kitchen herbs and salad crops you pick to eat, so no tansy leaf ends up in a harvest.

Penn State Extension lists tansy among the daisy-family flowers that draw larger predators such as lady beetles. A pot at the edge of the vegie patch puts those insects close to the crops while keeping the roots contained.

Harvesting Leaves and Flowers

Cut leafy stems once plants are bushy, usually from about 13 to 15 weeks after sowing. For drying, cut flower stems in summer when most buttons in a cluster are fully yellow.

• Wear gloves and long sleeves, and cut on a dry day once dew has gone.
• Take no more than a third of a plant at one cutting.
• Cut stems low with secateurs, and discard damaged or discoloured leaves.
• Tie loose bunches of five or six stems and hang them in an airy, shaded place.
• Dry until the leaves are crisp and the flower heads feel papery.

Store dried bunches in a closed, labelled box in a cool, dry, dark place, apart from kitchen herbs. Fresh stems suit vases and informal bouquets, and dried flower heads hold their colour and shape in arrangements and wreaths. The leaves and flowers contain thujone, so read Safety before any other use.

Traditional use and history

Tansy is native to temperate Europe and Asia. Its name is usually traced to the Greek athanatos or athanasia, immortal, which botanists link to its long-lasting flowers. Grieve's A Modern Herbal gives a second reason: its old use in preserving the dead. Its English folk names include bitter buttons, golden buttons and parsley fern. In German it is Rainfarn, and in French tanaisie.

In the old burying ground beside Harvard, nineteenth-century antiquarians found a coffin stuffed with tansy and judged it to hold the college's first president. The man who recorded the dig doubted it. In some parts of New England, it is still the custom to take a tansy bouquet to the cemetery.

The Northern Cheyenne of Montana gave it the name yellow medicine. Grieve also records that it was one of the native plants dedicated to the Virgin Mary.

Safety

Happy Valley Seeds sells tansy as seed for growing, as an ornamental and insect plant. 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.

If someone collapses, stops breathing, has a seizure or has a severe allergic reaction, call triple zero (000). For any suspected poisoning, call the Poisons Information Centre on 13 11 26 without waiting for symptoms. Do not make the person vomit, and wash sap off the skin with soap and water.

Tansy is a separate plant from its relative feverfew (Tanacetum parthenium), which has white daisy flowers.

Common problems

No seedlings. See Germinating the seed and its list, When nothing comes up.

Tall, pale, floppy seedlings. Too little light on a windowsill stretches them. Move trays to brighter light and turn them daily. Read more

Tansy coming up everywhere. It has escaped its pot or barrier; see Three mistakes that matter and Cutting Back and Containing.

Stems flopping over. Shade and rich, moist soil both push stems up to 1.5 m and weaken them. Move it into full sun, stop feeding, and cut it back after flowering.

A dead patch in the middle of the clump. Older stems in the centre of a clump weaken after three or four years while the edges keep growing. Lift the clump and replant young outer pieces.

Sparse flowers in the tropics. Tansy comes from temperate Europe and Asia and grows best in cool climates. Expect it to be leafy and slow to flower in humid heat; see the Tropical row in When to plant.

Pests and diseases

Tansy has no serious pest or disease problems, though a few garden regulars feed on it.

Two-spotted mite (Tetranychus urticae). Spider mites can trouble tansy in some areas, and this one has a wide host range. It builds up fast in hot, dry weather and leaves yellow mottled or stippled patches, worst on the undersides of leaves. Hose the undersides of leaves, and avoid broad-spectrum sprays that kill the predatory mites and lady beetles that keep them down. Read more

Common garden snail (Cornu aspersum) and grey field slug (Deroceras reticulatum). Both graze seedlings at night in damp weather, and in a German field trial, slug damage cut tansy cover sharply after four years. Hand-pick them after dark, or scatter an iron-based snail bait thinly as the label directs. Read more

Damping off (Pythium species and Rhizoctonia solani). Seedlings rot at soil level and collapse, most often in wet mix. Use fresh seed raising mix and clean trays, and avoid overwatering. Read more

Prevention first

• Keep seed trays clear of rain and hose splash, which spread damping off.
• Water the soil deeply in dry spells, since stressed plants suffer most from mites.
• Check the undersides of leaves weekly through hot, dry weather.
• Clear leaf litter, boards and loose pots from around seedlings, where snails shelter.

Tips

1. Cut a few flower stems for the vase as the first buttons colour: they last well and dry on the stem.
2. Keep a mown or paved edge around any planting in the ground, so creeping shoots show early.
3. Label the pot and any seed you save, so tansy is never mixed up with feverfew or yarrow.