Try this method developed by Junaid U. Rehman, PhD. You can safely remove fire ants from your yard and garden with no dangerous chemicals!
A shovel, heavy trash bag, baby powder, a bucket with air-tight lid (any old paint bucket with tight lid) and diatomaceous earth.
Spread the baby powder around the fire ant mound to stop them from escaping.
Place the trash bag inside the bucket.
Dig out the fire ant mound and dump in the bag inside the bucket. Make sure to dig out all the ants (or as many as you can).
Knot the bag. A zip tie works well if you have one.
Tightly close the lid of bucket. Make sure the lid is airtight.
Spread diatomaceous earth in the pit, so any remaining ants die.
Leave the buckets in the sunlight with lid closed for three to four days. Fire ants will die due to heat and lack of oxygen if temperature outside is 70F or higher.
Open the bucket and return the dirt to your yard or garden!