Introduced from Europe in the 1600s, the common tansy is a perennial which reproduces both by seed and roots, says abinvasives.ca. It is a noxious weed in Alberta. While still sold at nurseries and herbal remedy suppliers, gardeners should not plant it.
Cultivation makes tansies spread quicker. The most effective control method is mowing combined with chemicals and encouraging the growth of native plants.
Tansy “stems are branched, erect, often purplish-red, and dotted with glands. There are many stems per plant and grow up to 1.5 m tall.
“Leaves alternate on the stem and are deeply divided into numerous narrow, individual leaflets with toothed edges.
“Flowers are yellow, numerous, and button-like, occurring in dense, flat-topped clusters at the tops of the stems.
“Seeds are yellowish brown achenes with short, five-toothed crowns.”