Herb · Asteraceae
Common Tansy
Tanacetum vulgare
A rugged golden-flowered herb that runs on almost nothing and takes off the moment it settles in.
Full sun
Every 7–14 days
50–86°F · 10–30°C
USDA 3–8
Overview
Common tansy is a joy to spot: a hardy perennial in the daisy family, topped with flat clusters of button-shaped golden-yellow flowers over ferny, sharply scented leaves. It sailed over from Europe as a garden and medicinal plant and quickly made itself at home across North America. Crush a leaf and a bitter, camphor-like scent leaps out, calling the plant by name before you even see the flowers.
Vigor is what tansy is all about. It powers through poor soil, drought, and cold clear down to zone 3, and it hits its stride fast once the roots grab hold. That drive comes with a catch worth respecting, since creeping rhizomes and eager self-seeding send it well past its bounds, and several states brand it a noxious weed. Give it a spot you can hold the line on, or leave it be where the rules say no.
One fact anchors all the enthusiasm. The whole plant packs thujone and sesquiterpene lactones, which make it toxic to pets, livestock, and people, so grow it for its looks and its pest-shooing scent and keep it far from the kitchen.
Care
The short version: hand it full sun and free-draining soil, water it only while it roots or through a long dry spell, and stay sharp with deadheading and dividing so it never bolts out of bounds.
Light
Aim tansy at full sun and it responds with strong, upright stems and its biggest burst of bloom. It gets by in partial shade, but it stretches taller and floppier there and trades away a good share of those golden buttons, so the brighter the better.
Water
Give the roots time to grab hold and tansy turns genuinely drought tolerant, thirsting only through a long dry spell. Soak young plants until they take, then back right off, because soggy soil trips it up far more than any dry stretch ever could.
Soil
Tansy tackles dry and poor soils head-on, yet it truly hits full stride in moist, humus-rich ground. It stays easy about pH, thriving anywhere from 6.0 to 8.0, as long as the water drains clean away.
Temperature
Tansy powers along through a wide band of about 50°F to 86°F (10°C to 30°C), and its tough roots punch through winters down to zone 3. Heat waves and cold snaps barely slow it once it has dug in.
Humidity
Tansy leans dry, favoring roughly 30% to 60% humidity, which most open gardens serve up without a thought. Damp, stagnant air is the one thing that drags it down, so keep the breeze moving.
Feeding
Skip the fuss, because feeding is mostly unnecessary for a plant that charges ahead in lean ground. A little compost or a balanced fertilizer in spring covers it, and piling on more only revs up an already restless spreader.
Pruning
Clip the spent flower heads before they set seed and you shut down the self-sowing before it starts. Then chop the stems near ground level in late fall or early spring to clear the deck for next year's charge.
Repotting
Split a potted tansy every 1 to 2 years, staying ahead of circling roots and a crowded crown. In the ground, lift and divide the clump every few years to fire up fresh growth and keep its reach in bounds.
Size & spacing
Tansy shoots up anywhere from 1 to 5 feet (30 to 150 cm) depending on how it is grown, so hand it real headroom. Each clump bulks out to about 9 to 18 inches (23 to 46 cm) across before the rhizomes start striking outward.
When to plant
Tansy marches to the beat of a cold-hardy perennial, and the season is easy to work with. Fire up seed indoors in late winter, send the young plants out after the last frost once the soil warms, and watch the golden heads blaze 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
Here is the upbeat truth: tansy shrugs off almost everything, so trouble usually traces to too much water or its own drive to spread rather than any weakness. Catch the early signs below and a quick move keeps the whole patch charging ahead.
Tansy charging across the bed and popping up far from where it started
That is aggressive spread in full swing, and tansy runs it on two engines at once. Creeping rhizomes fling new shoots well past the clump while dropped seed slips into every gap. Deadhead before the flowers set seed, dig the rhizomes out to the very last fragment, and mow or cut the patch through the season to grind its momentum down.
Fix:
- Deadhead before seed set
- Dig out rhizomes including root fragments
- Mow or cut repeatedly through the season
Lower leaves yellowing where the ground stays soaked
This one is all wet feet. Poor drainage or overwatering keeps the soil soggy, the roots go dark and soft, and the bottom leaves flag yellow. Open up the drainage and dial back the watering, and a plant this drought-tough springs right back into gear.
Fix:
- Improve drainage
- Reduce watering frequency
Soft insects swarming the fresh shoot tips
Those are aphids, soft-bodied insects that pile onto the newest growth and drip sticky honeydew as they feed. Knock them loose with a hard jet of water, then bring in insecticidal soap if they rally. Even better, tansy calls in predatory insects on its own, so leaving a few often lets the beneficials mop up the rest.
Fix:
- Spray with a strong jet of water
- Apply insecticidal soap
Toxicity
One serious note cuts through all the excitement. The whole plant carries thujone and sesquiterpene lactones that spark vomiting, drooling, and tremors, and in larger amounts they damage the organs and, in people, end a pregnancy. Pull on gloves to work with it, and keep it well clear of pets, grazing animals, and children.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Toxic
A cat that chews tansy quickly drools and vomits, with diarrhea and a raw, sore mouth right on its heels. Keep the bigger nibbles out of reach, because the thujone inside can ramp up to tremors and worse.
Dogs Toxic
In dogs, tansy sets off vomiting, diarrhea, and an itchy rash wherever they gnaw the leaves. A big or repeated dose blows past a mere stomach upset into trembling, seizures, and damage to the liver and kidneys, so block their access to it.
Horses Toxic
Most horses wheel away from tansy at its bitter reek, but any that eat it wind up with a churning gut and a dull, flat mood. The thujone stacks up fast with quantity, so steady grazing courts tremors and organ strain.
Rabbits Toxic
The very oils that drive off other animals make tansy a bad bet for rabbits, kicking off drooling and digestive upset. Keep it off their menu flat out rather than gambling on a small taste.
Livestock Toxic
Cattle, sheep, and goats mostly steer wide of the bitter plant, yet hungry animals on overgrazed ground will tear into it. In quantity the thujone and sesquiterpene lactones can trigger vomiting, staggering, and convulsions.
Birds Toxic
The aromatic oils that send insects packing hit birds just as hard, so the foliage and seed are no treat to offer. Rule the whole plant out for backyard poultry and pet birds alike.
People Caution
No part of tansy is safe to eat, whatever the old kitchens and remedies once claimed. The thujone can fire off vomiting, drooling, and tremors, it works as an abortifacient, and a real dose wrecks the organs, so handle it in gloves and keep it well 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
The wild species is the tansy most growers chase, but a couple of standout garden selections are worth hunting down for their looks.
Tanacetum vulgare var. crispum (Fern-leaf or Curly Tansy)
Its leaves come more finely cut, crisped, and curled than the wild plant's, delivering a tidier ornamental that also spreads with far less abandon.
'Isla Gold'
Growers chase this one for its electric golden-yellow ferny foliage, a jolt of color that earns its spot on leaves alone.
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
Multiplying tansy is a thrill precisely because it is so easy, from seed or from a split clump, so the real sport is deciding when to rein it back rather than push it on.
SeedEasy
Spring · Germinates in 1 to 2 weeks; typically blooms by the second year
Sow seed in spring and it bursts up in just 1 to 2 weeks, though the plant holds its flowers back until the second year. Tansy self-sows with real gusto, so snip the spent blooms to stop it striking out where it is not wanted.
DivisionEasy
Spring or fall · Establishes within one growing season
Heave up an established clump in spring or fall and tear it into pieces, since nearly every scrap of rhizome roots fast and locks in within one growing season. It is the quickest route to a whole batch of new plants and a prime chance to cut a runaway clump down to size.
Myths
Tansy is a safe cooking and healing herb because old recipes swore by it.
Old cooks and healers did lean hard on tansy, but the science has moved on. The plant is loaded with thujone, which makes it unsafe to eat even in small amounts. Grow it with gusto in the garden and keep it clean out of the kitchen.
Set out tansy and every garden pest clears off for good.
Tansy genuinely turns some insects away, so the claim has real roots, but it is no all-out shield. It also reels in a few pests right alongside the beneficial bugs, so put it to work as one sharp tool, not a magic cure.