One master gardener reports using Spinosad for fire ants in an herb garden. She mixed the product with water and poured it over the mound. Spinosad also comes as bait, which is taken into the mound by foraging ants and fed to the queen. When the queen dies, the mound dies.
This process may take longer than products that immediately kill the mound. It is organic and can be effective for several months, even preventing new mounds from forming.