Tansy Tanacetum vulgare

Common Tansy is an aromatic herbaceous perennial that has fern-like foliage and yellow button-like flowers. The plant grows erect and averages 1-5 feet tall. It spreads rapidly by its rhizomatous root system and prolific seed production. The plant has been listed as a noxious weed in many areas of the United States, mostly in the central and north western part of the country. Common Tansy is a member of the Asteraceae or Aster family. 

The plant is native of Europe and Asia. Common Tansy was brought to North America by early settlers in the 1600s for medical and horticultural purposes. It was used for the treatment of constipation, hysteria, intestinal worms, rheumatism, and digestive disorders. The leaves were used to wrap corpses to prevent rapid decay. They were also used to protect meats from flies and ants. More recently, Common Tansy has been researched for use as an insecticide or mosquito repellent. The plant has naturalized in the northern United States and southern Canada. It is found along roadsides, railroads, pastures, streams, and ditches.

The genus name, Tanacetum, is derived from the Greek word, "Athanasia," which means"immortal." The species name, vulgare, is Latin and means "common."

Common Tansy prefers full sun to partial shade. It grows in well-drained soils. It tolerates a variety of soils including dry and poor soils, but it actually prefers moist humus soils. Common Tansy is problematic since it forms a dense cover, completes with native plants, and degrades pasture land. The plant reproduces by seeds, rhizomes, and root fragments. It is important to deadhead or shear off blooms to control self-seeding. Hand pulling and mowing may also help to reduce seed production if properly timed. Common Tansy can be controlled with common herbicides. The best defense is to provide better land management and develop a long-term ecological strategy.

Common Tansy contains an oil known as thujone, which may cause skin irritation or contact dermatitis. When handling this plant, it is important to wear gloves and long sleeve shirts to avoid exposure.

Thujone is a potent chemical, and excess consumption may cause convulsions or death. Common Tansy can be toxic to horses, cows, and humans especially if eaten or used in excess. However, sheep and goats can tolerate the plant and have been used to control the weed.

The leaves are feathery, fern-like, and have a pungent camphor-like odor when crushed. The flowers are clusters of golden yellow buttons that bloom from July to September. The fruits are tiny dark brown seedheads that mature in late summer to fall.

When considering Common Tansy in your garden, it is important to be aware that the plant is an invasive noxious weed, and it is prohibited or restricted in some areas across the United States. It is prohibited in Colorado, Minnesota, Montana, Wyoming, and parts of Washington State. If planted, it is important to clip off the spent flowers to control self-seeding. It is not recommended for flower beds or borders due to its spreading rhizomes.

Quick ID Hints:

• Green feathery, fern-like leaves
• The leaves have a strong pungent odor when crushed
• The flowers are golden yellow button-like blossoms
• The stems are reddish-brown in color

Insects, Diseases, and Other Plant Problems:  Common Tansy has no serious pests or disease problems. Spider mites can be a problem in some areas. The plant can be very aggressive when in the optimum environment. Reported as invasive in MD, MN, ID, OR, WA, WI, and WY. See native alternatives to the left.