Herb · Asteraceae
Common Tansy
Tanacetum vulgare
Flat-topped clusters of button-shaped golden-yellow flowers rising over ferny, sharp-scented leaves.
Full sun
Every 7–14 days
50–86°F · 10–30°C
USDA 3–8
Overview
Common tansy shows a clear, recognizable form up close. Flat-topped clusters of small, button-shaped golden-yellow flower heads sit at the tops of the stems, each head a tight, flat-faced golden disc. Below them the foliage is ferny and finely cut, divided into narrow, feathery segments of deep green. It is a hardy perennial in the daisy family, carried from Europe and now common across North America, and every part of it holds a bitter, almost camphor scent that rises the moment a leaf is bruised.
Everything about the plant points to vigor you can see. The stems climb fast and hold themselves upright, dense with the same finely cut leaves from base to tip. Out of sight, creeping rhizomes snake outward and send up fresh shoots well past the parent clump, and the spent heads dry into seed that drops and sprouts close by. That drive, hardy to zone 3 and untroubled by poor, dry soil, is why several states brand it a noxious weed.
The same leaves and stems that smell so sharp are the reason to keep it at arm's length. Throughout the plant, from root to golden flower, run thujone and sesquiterpene lactones that make it toxic to pets, livestock, and people. Those oils are what give the crushed foliage its bitter bite, and they mark tansy as a plant to look at rather than to eat.
Care
The short version: those button flowers and ferny leaves come easiest in full sun and well-drained soil, with water only while the plant is young or through a long dry spell, and steady deadheading and dividing to keep the spreading clump in hand.
Light
In full sun the stems of tansy grow thick and stand firm, and the golden button heads come in their fullest numbers. Set in partial shade, the same plant stretches taller and floppier, its stems leaning, with fewer of those bright discs at the top.
Water
Once its roots take hold the plant is drought tolerant, its ferny leaves holding up through a long dry spell without wilting. Young plants want a soak until they root, and after that soggy ground does more harm than dryness, softening the roots that keep it upright.
Soil
Tansy grows even in dry and poor soils, though in moist, humus-rich ground the foliage comes lusher and deeper green. It roots across a pH of 6.0 to 8.0, asking only for soil loose enough to drain.
Temperature
The plant stays in active green growth across roughly 50°F to 86°F (10°C to 30°C), and its rootstock is hardy enough to hold through winters down to zone 3. Neither summer heat nor hard cold marks the foliage once the plant is settled.
Humidity
Tansy keeps its best form in dry, moving air, near 30% to 60% humidity. In damp, stagnant air the crowded leaves are slow to dry, the one setting that spoils their crisp, ferny texture.
Feeding
Feeding is mostly unnecessary, since the plant makes dense, healthy foliage on lean ground alone. A little compost or a balanced fertilizer in spring is plenty, and richer soil only pushes soft, sprawling growth and wider spread.
Pruning
Cutting off the spent flower heads before they brown and set seed keeps the plant from sowing itself across the bed. When growth dies down, the stems come off near ground level in late fall or early spring, leaving a low crown that flushes fresh, feathery leaves again.
Repotting
In a pot the clump tightens and should be split every 1 to 2 years, once the roots begin to circle and the crown grows congested. In open ground, lifting and dividing every few years opens up the crowded crown and checks the creep of the rhizomes.
Size & spacing
Grown well, tansy stands 1 to 5 feet (30 to 150 cm) tall, an upright column of ferny foliage topped with gold. Each crown widens to about 9 to 18 inches (23 to 46 cm) across before the pale rhizomes push new shoots out past that edge.
When to plant
Tansy moves through the year like a cold-hardy perennial. Seed goes in indoors in late winter, the young leafy plants set out after the last frost once the soil warms, and the golden button heads open and hold their color from July through September.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: 6 to 8 weeks before the last spring frost
- Plant: After the last spring frost once soil has warmed
- Harvest: Blooms July through September
Hardiness
USDA hardiness zones: 3–8
Temperature: down to -40°C
Troubleshooting
Most of what goes wrong with tansy shows on the plant itself: leaves that yellow, tips that crawl with insects, or shoots that appear where none were set. The close-up signs below point to the cause, so a quick look tells you what to do.
Fresh shoots of ferny tansy rising well beyond the original clump
This is aggressive spread, written in the plant's own parts. Pale creeping rhizomes travel outward under the soil and lift new leafy shoots past the clump, while the dried heads shed seed that sprouts in the open gaps. Cut the heads before they set seed, dig the rhizomes out to the last white fragment, and mow or cut the patch through the season to drain its strength.
Fix:
- Deadhead before seed set
- Dig out rhizomes including root fragments
- Mow or cut repeatedly through the season
Lowest ferny leaves fading to yellow on plants in wet soil
The trouble is poor drainage or overwatering. Standing water softens the roots to a dark, mushy state, and the lowest leaves lose their green and turn yellow first. Loosen the ground so it drains and water less often, and the drought-hardy roots firm up and the foliage greens again.
Fix:
- Improve drainage
- Reduce watering frequency
Soft-bodied specks massed on the tender new leaf tips
Those specks are aphids, small soft insects packed onto the youngest growth, their feeding leaving a sticky, shining film of honeydew on the leaves. A hard jet of water knocks them from the stems, and insecticidal soap clears any that return. Tansy's own flowers pull in predatory insects, so a few aphids left in place often draw the hunters that finish them.
Fix:
- Spray with a strong jet of water
- Apply insecticidal soap
Toxicity
The bitter oils you smell in a crushed leaf are a warning made plain. From the pale roots up through the stems to the golden heads, the whole plant carries thujone and sesquiterpene lactones that cause vomiting, drooling, and tremors, and in quantity they damage the organs and, in people, end a pregnancy. Handle the foliage in gloves and keep the plant away from pets, grazing animals, and children.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Toxic
A cat that bites the ferny leaves soon drools and vomits, with diarrhea and a raw, sore mouth close behind. The thujone packed in the foliage can carry a larger dose on to tremors and worse, so keep it out of reach.
Dogs Toxic
A dog that gnaws the stems and leaves vomits and scours, and an itchy rash rises where the sap met the skin. A large or repeated mouthful runs past that upset into trembling, seizures, and harm to the liver and kidneys.
Horses Toxic
A horse usually swings its head from the bitter smell, but one that grazes the plant takes on a churning gut and a dull, flat look. The thujone in the leaves mounts with each bite, so steady feeding risks tremors and organ strain.
Rabbits Toxic
The same sharp oils that fill the leaves make tansy wrong for rabbits, setting off drooling and a churned-up gut. The whole plant is best kept clear of the hutch rather than tried in any amount.
Livestock Toxic
Cattle, sheep, and goats mostly walk past the bitter foliage, but hungry stock on bare ground will pull at it. Taken in quantity, the thujone and sesquiterpene lactones in the leaves and stems bring vomiting, staggering, and convulsions.
Birds Toxic
The aromatic oils that soak the foliage and seed are as unfit for birds as for insects. Neither the leaves nor the dry seed heads should reach backyard poultry or pet birds.
People Caution
No part of the plant, leaf, stem, or golden head, is safe to eat, whatever the old kitchens once did with it. The thujone in the tissue can bring on vomiting, drooling, and tremors, it works as an abortifacient, and a real dose harms the organs, so wear gloves against the foliage and keep it clear of children.
Wear gloves when handling; the aromatic foliage can cause contact dermatitis in sensitive people.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
Most tansy wears the plain wild form, but a couple of selections stand out for the exact look of their leaves.
Tanacetum vulgare var. crispum (Fern-leaf or Curly Tansy)
Its leaves are cut finer still than the wild plant's, their edges crisped and curled into a densely ruffled, feathery texture, and it spreads less freely too.
'Isla Gold'
This selection trades the usual deep green for bright golden-yellow in its ferny leaves, the color carried in the foliage rather than only the flowers.
Companions
Tansy earns its keep next to roses and fruit trees, where its scent helps turn away some pests and draw in beneficial insects, but it's a poor neighbor for small vegetables it can quickly crowd out.
Plant near
Roses: Traditionally interplanted to help deter some insect pests and to attract beneficial predatory insects.
Fruit trees: Used as an aromatic companion thought to repel some pests while drawing in pollinators and predators.
Keep apart
Low-growing vegetable beds: Aggressive rhizomatous spread and heavy self-seeding can crowd out less competitive crops.
How to propagate
New tansy comes readily from a scatter of dry seed or from a split of the creeping rootstock, so the work lies in slowing it rather than starting it.
SeedEasy
Spring · Germinates in 1 to 2 weeks; typically blooms by the second year
Dry seed sown in spring breaks into green in just 1 to 2 weeks, though the plant sends up leaves the first year and holds its golden heads back until the second. It sheds seed freely on its own, so clip the browning heads before they scatter if the ferny shoots are not wanted all around.
DivisionEasy
Spring or fall · Establishes within one growing season
An old clump lifted in spring or fall pulls apart into rooted pieces, each length of pale rhizome carrying buds that settle and leaf out within one growing season. It is the fastest way to raise more plants and the moment to cut back a crown that has crept past its place.
Myths
Tansy is a safe culinary and medicinal herb because old recipes once used its leaves.
The ferny leaves did once flavor old dishes and remedies, but they are no longer trusted. They hold thujone, which makes the plant unsafe to eat even in small amounts. Enjoy the look of the foliage and the gold heads, and keep both out of the kitchen.
The scent of tansy keeps every garden pest away.
The bitter, camphor-like oil in the leaves does turn some insects back, so the scent is not empty, but it is no wall. It also draws certain pests in alongside the beneficial insects, so lean on it as one part of the picture rather than a cure.