Common tansy

Identification & Biology
Alias' : Garden Tansy
Latin Name : Tanacetum vulgare
Category : Terrestrial Plants
Description :
  • Perennial that reproduces by seed and rhizomes
  • Grows from 1.5 to 2.0 m in height with purplish-red stems at maturity
  • Many yellow disc flowers that resemble buttons are found at the top of the plant in a flat-topped cluster
  • Leaves are dark green and divided with serrated leaflets
  • Leaves and stems are strongly aromatic when crushed


Flowering typically occurs from July to September. Flower heads remain intact and can hold seeds through the fall until they are physically dislodged from dried flower heads. Seeds are spread by wind, water, birds, other animals and on vehicles. Established plants also spread by creeping rhizomes forming dense patches. Seeds can remain viable for up to 25 years, so stopping seed spread is a main concern.

Common tansy is sometimes confused with tansy ragwort. The two “tansies” are most readily distinguished by their flowers. Tansy ragwort has outer ray petals on its blooms while common tansy has button-like blooms with no outer petals.

Look Alikes

In British Columbia, common tansy is most prevalent in the central and southern interior, as well as the lower mainland, Fraser Valley, Squamish/Pemberton, Vancouver Island and other coastal areas. Common tansy prefers sunny areas with well-drained soil, and often infests stream banks, pastures, and disturbed sites such as roadsides. It cannot effectively establish in frequently tilled soils.

Impact & Risks
  • Common tansy contains alkaloids that are toxic to both humans and livestock if consumed in large quantities. Cases of poisoning are rare as tansy is unpalatable to most grazing animals.
  • It can reduce the productivity of pastures for livestock and threatens the ecological health of natural areas.
Prevention & Mitigation

The most effective way to ensure that your lands do not become infested with common tansy is by prevention. Here are some recommendations to prevent common tansy from invading your property:

  • Maintain your crops and natural lands in a healthy, vigorous condition to ensure a competitive plant community; competitive perennial grasses and forbs utilize water and nutrients that would otherwise be readily available to common tansy.
  • Regularly patrol your property for common tansy plants and immediately control or remove infestations before seed set. Do not leave plants to compost as they may still produce viable seed.
  • Cooperate with adjacent landowners and encourage them to prevent common tansy spread.
  • Immediately re-vegetate disturbed, bare soils with a suitable seed mixture that provides dense, early colonization to prevent weed invasion.
  • Do not move contaminated soils to a new area.
Treatment & Disposal
  • The most effective control method combines mowing or hand-cutting with chemical control and encouraging competition from native vegetation.
  • Regular mowing of common tansy can reduce seed production but must be repeated to eliminate regrowth from rootstock.
  • Hand-pulling may be used in areas where mowing and herbicide application are not feasible. Gloves and other protective clothing should be worn to prevent skin irritation.
  • Common tansy is unpalatable to cattle and horses, but sheep and goats are reported to graze on it.
  • There are no biological controls for common tansy at this time.
  • Before applying herbicides, read the label for full use and precautionary instructions. For further information on the selection and application of chemicals to protect your crop, contact AgriService BC at 1-888-221-7141 or email
Okanagan Distribution

Priority Level Definitions

Watch For - Poses a significant threat (very high risk) and does NOT presently occur in the region OR is relatively new to the region and is very limited in extent.
High - High risk/impact; limited population with significant potential to spread in the region.
Medium - Medium risk/impact; limited distribution – broader population distribution with potential to spread further in a region.
Low - Low risk/impact; may be widespread or not, may be of concern in specific situations with certain high values – e.g. specific agriculture crops. Some species may be treated primarily with biological control agents.