Common Tansy (Tanacetum vulgare )
Aster Family / Aster Subfamily Subfamily / Chamomile Tribe
By Thomas J. Elpel with additions by Pamela G. Sherman
About Common Tansy: Common Tansy is a native of Europe, also known as Chrysanthemum vulgare. It was brought to this country for medicinal and horticultural purposes. This perennial plant spreads via an extensive, spreading root system and profuse seed production. It especially favors the disturbed soils along ditch banks, where the water quickly spreads the seeds for miles downstream. Common Tansy is now widespread from coast-to-coast across most northern states and Canadian provinces. Despite extensive infestations along ditches, creeks, and roads, the plant is not yet listed as a noxious weed in many places. Most alarming, you can still buy the seed and grow more!
The pilgrims brought common tansy seed to the United States as early as 1631, because of its many medicinal uses... In the 1600s, the Massachusetts governor called common tansy a necessity... and encouraged even more extensive planting in the garden... Europeans and colonial Americans used common tansy in a face wash to lighten and purify skin, to treat ulcers, constipation, and hysteria, to restore menstrual flow, treat intestinal worms, rheumatism, jaundice, and digestive problems, and in large doses to induce abortion [women have died from this] but in smaller doses it was thought to prevent miscarriage and increase fertility... The northern Cheyenne of Montana called common tansy "yellow medicine", and its leaves and flowers were made into a tea and given to those feeling weak.
From the 1660's to the 19th century, European-Americans have wrapped corpses in tansy to retard decay, much as tansy leaves were used to ward flies, ants and fleas off uncooked meat, thus keeping it fresher longer.This worked especially well if the tansy was mixed with elder leaves (Sambucus spp.).
In the mid-1970s, common tansy was planted on mine sites being reclaimed in Wyoming . Common tansy has more recently been the subject of research for possible use as a repellent or insecticide for mosquitoes and Colorado potato beetles.
Tansy also gives a green and a yellow dye.
Common tansy is rich in volatile oils (see Botany in a Day). The aromatic fresh young leaves and flowers may be used sparingly as a substitute for sage in cooking. The main volatile oil is thujone, a potent and bitter chemical often used medicinally as a wash to treat roundworm, or internally to expel worms and cause abortions. Excess consumption of thujone for medicinal purposes has caused convulsions and death. It should not be used without medical supervision. The volatile oil can be distilled from the plants and is marketed commercially.
Most used is blue tansy, but sometimes common tansy as well, or simply "tansy" is advertised. After listing a multitude of health benefits, a number of companies also include disclaimers like this one: "Tansy oil is a potent poison due to presence of high concentration of thujone and even small doses can be fatal. It can also trigger hallucinations and severe nervous or neurotic disturbances, while having addictive, narcotic effects." "The essential oil in the leaves is toxic and as little as oz can kill an adult." It should not be used without skilled medical supervision.
Tansy is noted as a good mineralizer for the compost pile, as long as the roots and seed heads are removed to limit its spread. On the other hand, reports of its invasive impact are mostly anecdotal... "detailed study and documentation are lacking."
Mechanical Controls: Pulling or mowing has little effect on tansy, except to reduce seed production. Most of the big roots are near the surface, so it may feel like you can pull up smaller plant roots and all, but it almost always comes back again and again. Tansy regenerates from root fragments, so cultivation could expand the size of an infestation.
As with most abundant plants, "common tansy control is likely most effective when it employs a long-term, ecosystem-wide strategy rather than a tactical approach focused on battling individual" stands.
Persistent hand-pulling may be effective in controlling small populations if most or all rhizomes are removed. Seeding areas disturbed by hand-pulling with desired species may decrease the potential for reestablishment... Common tansy can cause dermatitis... so precautions should be taken when hand-pulling.
Several sources indicate that common tansy populations may be controlled through mowing.
Fire: Dense patches of dried tansy stalks burn very hot and fast. Controlled burns in the spring can help reduce fire danger later in the year. Removing the dead vegetation also makes the plants easier to target with herbicides or grazing animals, although repeated burns may increase weed habitat.
Grazing: Horses and cows sometimes browse the tender young leaves of the common tansy, but they leave it alone as it matures. Tansy could be toxic to these animals in excess. Sheep and goats however, eat the plant with great enthusiasm. My town in plagued by extensive infestations of tansy, and we have begun working with sheep to control the weed. It is truly amazing to set the animals loose in a tansy patch and watch it all disappear. The sheep remove the tansy, allowing light to the grasses below. As a result of our sheep project I realized we did not have a weeds problem so much as a lack-of-sheep problem. If we can increase the number of sheep in the community then we will never have to worry about tansy again!
Chemical Controls: Tansy is relatively easy to control with common herbicides like 2,4-D, or a blend of 2,4-D and clopyralid (Curtail®), or picloram (Tordon® 22K), however the weed patches must be monitored and retreated to kill any tansy that regenerates from the roots. Herbicides are impractical in many cases where the weed is inter-mixed with other desirable plant species. Special care must be taken along ditch banks and creeks to avoid contaminating the water.
Important: Most "weed problems" are really "people problems" from poor land management and a lack of ecological insight. It is easy to reach for a tool like fire, mowing, or herbicides to attack an out-of-control weed, but often those tools do little to get to the root cause of the weed infestation, and sometimes make the problems worse. Please read more about range ecology, desertification, and invasive weeds on this website before applying any tool of weed control Go to: Desertification and Invasive Weeds.
- Thomas J. Elpel. Botany in a Day. HOPS Press: Pony, MT. January 2000.
- http://www.pfaf.org/user/Plant.aspx?LatinName=Tanacetum+vulgare referencing
- John Lust and  Dr. James Duke and Stephen Foster
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