Tansy was a part of the Acadian medicine chest and was considered necessary in a garden by the British. It is used to repel insects, particularly flies, and to guard against worms. Acadians used it internally to expel intestinal parasites, and in New England it was added to coffins to guard against the dead being consumed by worms. It was used this way so much in the colonies during the 19th century that it became associated with death. Bruised leaves were placed on meat to keep flies at bay, and it was kept strewn about in homes with dried elder leaves to repel other insects. Colonialists would wear it in their shoes to guard against insect born illnesses. It is said that infusions of the root, flowers or seed can be a strong antidote for gout. The Irish would bathe in infusions of tansy and salt to ease joint pain. Up until the 1940s, diluted tansy oil was added to fleabane & pennyroyal to make a popular insect repellent. More recently, Swedish scientists have found it fairly effective at repelling ticks. The leaves and flowers are toxic if consumed in large quantities.
In addition to the way settlers used the plant, indigenous populations found this herb to be effective in addressing a broad range of ailments. Pulverized blossoms & leaves were infused by Cheyenne to improve weakness & dizzyness. Chippewa found that a weak infusion aided earaches, and that the roots either brewed or chewed were effective against a sore throat. Many tribes used it against stomach disorders and fever reducers. Micmac and Malecite used it as a contraceptive and Cherokee would tie it around the waist of a pregnant woman to avoid miscarriage during pregnancy. The Shoshoni used it as a warm anaseptic wash and Ojibwe would include it in a blend of dried plants that was burned to attract deer.
Tansy had culinary uses that are not generally practiced today. Because of the toxicity, some people react to consuming even small amounts. New leaves emerging in spring were used as an herb to add to omelettes or puddings, and paired with caraway when making biscuits and ‘tansy cakes’. Today it is only known to make a particular type of blood pudding in Cork, Ireland. The flowers are cultivated for aesthetic purposes and may be used to make a yellow or green hued dye. It is still used as a companion plant for non-chemical pest control, demonstrated to be highly effective against the Colorado potato beetle. When planted alongside cucurbits like cucumbers, melons and squash, or with roses and berry plants, it repels pests like ants, cucumber beetles, Japanese beetles and squash bugs. Beekeepers will sometimes add dry tansy to the blends they use to smoke out beehives.
Sources: The Harriet Irving Botanical Gardens on the Acadia University campus, Nova Scotia, Wikipedia, A Modern Herbal by Mrs. M Grieve and Native American Ethnobotany by Daniel E Moerman. Please note that material provided here is for informational purposes only and are not to be taken as recommendations for treatment.