How to Kill Ants in Plant Roots

Although pesky, ants do have benefits for a garden. For example, they help to clean up fallen debris and aerate the soil. Ants rarely harm the plants themselves, although they sometimes encourage the activity of aphids and other insect pests. If you notice unwanted ant activity in and around your plants' roots, you have several options for eradicating them.

An ant colony can sometimes move into a potted plant, which is especially problematic for houseplants. Find a bucket that's larger than the plant pot itself.

Place the pot inside the bucket and fill the bucket with an insecticidal soap solution made by combining 2 tablespoons of insectidal soap concentrate for every 1 quart of water. Use enough water the pot is fully submerged. Allow the potted plant to soak in this soapy solution for approximately 24 hours, which effectively kills all of the ants without harming the plant's roots, then remove the potted plant and flush the soil it with fresh water to get rid of the soap. Don't leave the pot in the water much longer than 24 hours or you could affect plant health.

Use insecticidal soap concentrate, which you can buy at most garden centers and home improvement stores.

Diatomaceous earth -- a fine powder made from the crushed, fossilized remains of ancient sea creatures, called diatoms -- kills ants on contact. You can use the powder on indoor plants as well as outdoors in the garden. Use versatile diatomaceous earth in a number of ways:

Dust the powder around the base of the plant. This will control any ants scurrying around the plant's roots and up the plant's stems.

Sprinkle diatomaceous earth directly on and around the entrance of the ant nest to eliminate worker ants coming and going from the nest. 

Spread the powder onto the plant's leaves and stems. This eliminates ants that are climbing on the plant. This also controls honeydew-producing pests, such as aphids, that may attract ants to the plant. 

Use food-grade diatomaceous earth, not the industrial powder sold for swimming pools.

Wear protective goggles and a face mask to avoid inhaling diatomaceous earth and keep it from getting in your mouth or eyes. While it's not toxic, it can cause significant irritation if inhaled or ingested.

You can buy commercially prepared ant baits from most garden centers and home improvement stores. Or, you can whip up your own low-toxic homemade concoction that successfully eliminates not just scavenging ants, but the entire ant nest.

Postcards

Honey and peanut butter

Boric acid

Measuring spoons

Test what kind of ant bait works for the specific ants you have. Dab a dollop of peanut butter onto a postcard and a dollop of honey onto another postcard. Place the postcards near the ant nest in your plant's roots.

Check the postcards after one day. The postcard that has attracted the most ants is the bait of choice for handling your specific ant infestation.

Mix 4 tablespoons of peanut butter or 6 tablespoons of honey with 3/4 teaspoon of boric acid. Boric acid kills ants while presenting minimal toxic risks to people and wildlife.

Place the bait near the ant nest in your plant's roots. The ants will take the food into their nest where the boric acid will eliminate the entire nest.

Although boric acid is generally safe, keep it away from pets and small children, especially when it's mixed with honey or peanut butter.