Common Tansy

Common tansy is an herbaceous perennial in the Asteraceae (daisy) family. It produces erect stems that may reach up to 5 feet tall. Stems are woody, but die back each year, and form in clumps. Leaves are alternately arranged and pinnately divided with toothed margins giving them a fern-like appearance. New plants or those arising from rhizomes may only have small, low growing leaves rather than stems. Common tansy flowers from early summer to fall. Flowers occur in corymbs (flat-topped clusters) at the end of stems. Flowers are small (¼ to ½ inches), composite flowers consisting of dense clusters of yellow disk flowers. Common tansy has a dense network of creeping, lateral roots. Seeds are small, 1 to 2 mm, dotted and ribbed. Seeds are tufted with a pappus allowing for some wind dispersion.

Common tansy produces the monoterpene ketone thujone which can be toxic to humans, livestock, and wildlife. While common tansy is usually avoided by wildlife and livestock, thujone can cause convulsions and spontaneous abortion in humans and is a known skin irritant. Care should be taken when handling this species.

Common tansy is native to Eurasia and was introduced to North America in the 1600s for a myriad of uses including use as a medicinal, insecticide, preservative, and ornamental. It spreads primarily by creeping roots creating dense infestations. It can be transported to new locations by seeds and root fragments. This species is primarily found in pasture, roadsides, landscapes, riverbanks and islands, and disturbed areas.

Prevention and cultural control strategies should be utilized as much as possible. There are not any biological controls for common tansy currently available.

Hand pulling and digging out of all lateral roots can effectively eradicate small patches of common tansy, but great care must be taken to ensure that all of the root system is removed. Mowing prior to flowering can prevent seed production; it also opens up the canopy of common tansy allowing for more thorough herbicide applications. Do not mow while seeds are present. Tillage is not recommended as this is likely to fragment and spread reproductive roots. Controlled grazing with sheep or goats may be effective in reducing seed production and depleting root stores. Both sheep and goats are capable of consuming large amounts of common tansy without toxic effects.

Large infestations and areas where manual removal is not practical can be controlled with herbicides. Herbicide treatments on common tansy should occur while flowers are in the bud stage. Fall treatments may be effective at killing the root system. Read the label before using any herbicide. Contact TCWP if you have any questions about application rates or how to use an herbicide.

• Common Tansy. Minnesota Department of Agriculture.
• Weed Report: Common Tansy (2013) DiTomaso, J.M, Kyser G.B., et al. Weed Control in Natural Areas in the Western United States. Weed Research and Information Center. University of California.
• Best Management Practices: Common Tansy (2010) King County Noxious Weed Control Program.
• Common Tansy (Tanacetum vulgare) (2024) Midwest Invasive Species Information Network.
• Common Tansy (Tanacetum vulgare) (2014) MontGuide. Montana State University Extension.
• Common Tansy. Washington State Noxious Weed Control Board.