An ant infestation can destroy your vegetable garden. Fire ants are particularly harmful because they often eat the vegetables, not just the foliage. Combating an ant infestation in your vegetable garden is more difficult than killing ants in your lawn, because many of the common insecticides used against ants can harm your vegetables. You must use low-intensity insecticides as an alternative.
Search your garden and the surrounding yard to find the anthills. Ants prefer not to build hills in garden soil, so normally you will find the anthills in other sections of your yard, even when ants appear most present in your garden. If you find no anthills in the garden itself, you can kill the ants using traditional, high-strength insecticide ant bait. You can purchase ant bait at gardening stores and some home supply stores. Apply the bait around your yard but not in the garden.
If you find anthills located inside your vegetable garden, you cannot use normal insecticides or you may damage your vegetables or make them unhealthy to eat. Instead, search for ant bait containing methoprene or spinosad. These chemicals are safe to use around vegetables. You can apply these insecticides inside your garden at the same time you apply traditional insecticides to the rest of your yard.
Ant bait insecticides do not kill ants immediately. They can take up to three weeks to work, and for best results should be applied throughout the year. Apply the insecticides in spring, midsummer and fall.
To kill ants with insecticides more quickly, you can dilute the insecticides with water and pour them directly on the anthills. Check the label of the insecticide to see how much water should be added. Pour 1 gallon of water on the anthill and in a 1-foot circle around the hill.
Insecticides are effective for killing ants, and methoprene and spinosad should not damage your vegetables, but if you prefer not to use them you can use boiling water instead. Boiling water must be poured directly onto the anthills, completely drowning the ants. Pour the water slowly so that it has time to move through the soil and does not overflow to other areas of your garden. Use at least 2 gallons for each anthill in the garden.
After you have poured water on all of the anthills, spray the spots with an even mixture of vinegar and water to kill any ants that were not drowned. Make sure to destroy all the anthills in both your garden and the surrounding yard.