Are they fire ants? If so, then Fertilome "Come and Get It" bait works well. It contains Spinosad, a relatively benign pesticide, and other brands are available. Another method is to make a soil drench using 1.5 oz of Medina Orange Oil with 3 oz of Dawn dish washing liquid in 1 gal of water. Neither method will harm your plants, and are even OMRI approved for organic vegetable gardens—I use both in my raised vegetable beds as well as containers. If you have a large colony of fire ants you may have to repeat.
