You can use household ingredients around the anthills on the surface of the ground and the worker ants will carry the ingredients back underneath the ground to kill the ants. Once you remove the ants, the anthills will not remain on your patio.
Borax
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Mix equal parts of Borax and powdered sugar in a bowl.
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Sprinkle the mixture generously around the anthills on your patio. The ants will find the powdered sugar attractive and they will carry the mixture underground into their nest where the borax will kill the ants. Over the next several weeks, you should notice the ant activity decline and stop.
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Repeat the borax application again two to three weeks later if you still see ant activity.
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Use the garden hose to wash away the remaining anthills after the ant colony dies.
Boiling Water
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Fill the teakettle with water and bring the water to a rapid boil.
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Pour the boiling water directly over the anthills, saturating the entire area well. The boiling water will seep beneath the ground into the ant nest.
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Repeat the boiling water application again if the anthills reappear.