Control the Habitat
You could control their habitat by destroying the favorable conditions that allow them to build their colonies.
Seal cracks around any paved areas in your garden which could be sources for their nests.
Try not to use more than 1/2 inch of mulch in the landscaping for your garden beds which could support the ants' home.
Use Boiling Water
This method would be effective if you repeat it several times until the nest is destroyed completely. Avoid spraying boiling water onto plants to prevent damage to them.
Sprinkle Diatomaceous Earth
Simply sprinkle about a 1/2-inch-thick layer of diatomaceous earth on the ants' trails and around their nests.
These minute crystals cut the bodies of the ants and kill them fairly quickly. However, this method is effective only for direct contact with ants that are exposed to it.
Spray Liquid or Powdered Insecticides
Spray the liquid insecticide on the ants' trails and nests repeatedly to kill the ants. You could apply powdered insecticides directly into the ants' nests which could destroy the colony over time.
You could also reapply this powdered substance to create a barrier for any future invasion by these ants.
Set Ant Baits
These baits are resistant to wind and water. Place the baits around ant nests and around areas where the ants move.
The ants will eat the bait and carry the remaining poison to their nests for the other ants which consume it. In this process, all of the ants will be killed.
The bait may work slowly, but it can destroy the ants' colonies completely.