Background for Tansy
A constituent of Tansy is Thujone, which is also a compound of the addictive drink Absinth, made from Wormwood. Thujone is a powerful but dangerous compound of Tansy. Thurjone It is also found in lesser amounts in Mugwort, Tarragon, Coriander, Oregano and Sage. Thujone has an effect on the brain, which in small doses can enhance performance, but in larger does can cause convulsions and death. Tansy oil is extremely toxic and should never be ingested.
Tansy main use is as an insecticide and insect repellent, keeping away flies, and many insects that would reside in the vege garden and feast on the growing plants. Planting a Tansy in the vegetable garden and around tomatoes will make for a better cleaner crop. The stink beetles (Shield bugs) are said to be unhappy residing close to tansy. I see many claims that Tansy is also an ant repellent, so planting around concrete terraces where ants seem to favour putting their nests may be a good option. Otherwise dry Tansy (warm shady place) and sprinkle the dried leaves around on ant infestations.
Best to buy a plant. Once planted out these plants will grow quite rapidly to approximately 1m in height and about 50cm wide. It can get a bit scruffy, so be prepared to trim some of the stems back when it is threatening to crowd other plants, although with a bright yellow flower it can be forgiven for its straggly appearance. It will take a trim easily. You can also divide the roots of this plant and plant more around, especially your vege garden
This information is not intended to diagnose, treat, cure, or prevent any disease.