John Polk wrote:
Tanacetum vulgare, (Tansy) planted around where ants enter will repel them. I don't know if it works for all ants, but they certainly quit entering our house with a few plants around the doors. They also repel some flies, gnats, and other thugs. They are a perrenial, quite hardy, and will give dense clusters of bright yellow flowers for much of the summer. Keep a careful eye on them, as they can become invasive.