Tansy (Tanacetum vulgare) is a great perennial herb to use as a natural pest-repellent. It is also commonly known as Common Tansy, Bitter Buttons, Cow Bitter, Mugwort, or Golden Buttons. Its leaves have a fernlike appearance, and the scent is similar to that of camphor with hints of rosemary. The leaves and flowers are said to be poisonous if consumed in large quantities. The plant’s volatile oil is high in thujone, a substance found in absinthe that can cause convulsions. Some insects, notably the tansy beetle, have evolved resistance to tansy and live almost exclusively on it.
Irish folklore of the mid-1800s suggests bathing in a solution of tansy and salt as a cure for joint pain. Bitter tea made with the blossoms of T. vulgare has been effectively used for centuries as an anthelmintic (vermifuge). Tansy cakes were traditionally served during Lent because of a superstition that eating fish during Lent caused intestinal worms. Note that only T. vulgare is used in medicinal preparations; all species of tansy are toxic, and an overdose can be fatal. The dried flowering herb of Tanacetum is used ethnomedically to treat migraine, neuralgia, and rheumatism, and as an antihelminthic, in conjunction with a competent herbalist to circumvent any possible toxicity. Formerly, tansy was often used for its emmenagogue effects, but rumors have implicated tansy in cases of miscarriage. Pregnant women should avoid this herb.
In England, bunches of tansy were traditionally placed at windows to keep out flies. Sprigs were placed in bedding and linen to drive away pests. Tansy can also be used as a companion plant in the garden, especially with cucurbits like cucumbers and squash, or with roses or various berries. It is thought to repel ants, cucumber beetles, japanese beetles, squash bugs, and some kinds of flying insects, among others.
It is also used by some traditional dyers to produce a golden-yellow pigment. The yellow flowers are dried for use in floral arrangements.