plant at the going-out-of-business sale at Fat Cat Farm. This photo shows that plant.
In the past, tansy was used medicinally, but it can be harmful, even fatal. They used to use it to induce abortions. It can cause poisoning.
It has also been used to repel ants and many kinds of harmful garden beetles, but I've not personally found it very effective against ants. People have also used it in the kitchen as a culinary herb in small amounts, but, again, it can be toxic to ingest too much. I'm not chancing it.
My tansy first flowered a year after I planted it. It normally flowers from July to September. Mine has already stopped blooming this year. How long it blooms may depend on the temperature . This shows my tansy in bloom July 30, 2014. As you can see, some of the leaves are dying back.
As you can see by following these photos, tansy can be an invasive plant. That's why many people restrain it by planting it in pots. I actually want it to be invasive, because I prefer it to the weeds that would otherwise grown in the same place. Nature doesn't like bare ground.