Common tansy (Tanacetum vulgare) is a perennial that spreads through both seed and short creeping roots. It was introduced from Europe in the 1600s for ornamental and medicinal uses.
Stems are erect, woody and purplish-red in color. There are many stems per plant and they may grow to 1.5m in height.
Leaves are borne alternately and are deeply divided into narrow leaflets. They have a very pungent odour when crushed.
Flowers and Fruit
Tansy has yellow button-like flowers borne in flat clusters at the tops of stems. Seeds are unremarkable; small, brown and untufted.
Tansy grows best in full sun and fertile, well-drained soil. It will readily colonize field margins and riparian areas.
Tansy forms dense stands that choke out competing vegetation. It contains toxic alkaloids that cause internal bleeding and can kill livestock and humans if ingested in high enough quantity. Due to its strong smell and bitter taste, tansy is rarely grazed by livestock, which decreases pasture quality.
Never plant tansy as an ornamental in your yard. Always maintain competitive vegetative cover along field corners and edges, and in ditches, easements, yards and parks.
Similar to Leafy Spurge, the toxic properties of tansy don't appear to affect sheep and goats, which have been used in Grande Prairie along the Bear Creek corridor to control this invasive weed.
Mowing is effective on tansy, so long as the plants are mowed before seed set and the mowing is repeated as regrowth occurs to deplete root reserves. If a homeowner only has a few plants in their yard, they are encouraged to dig out the whole plant, roots and all, bag it in garbage bags, and take it to the landfill for burial.
There are several products that are effective against tansy; consult your local Agricultural Fieldman for recommendations.