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Ants in the Garden: Ant Pesticides

AntsAnts are an important component of the garden ecosystem. Ants are cleaners: they eat and help decompose organic matter in the soil, enriching the soil. Ants also eat pest insects such as fleas, fly larvae, and termites. Ants tunneling in the soil improve soil aeration which is helpful to plant roots.

Ants become a garden pest when they eat living plants–usually seedlings, weak, or dying plants–and cultivate colonies of insect pests such as aphids, scale, and mealybugs (these bugs excrete a sugary substance called honeydew which ants eat–ants will farm these insects to ensure their own food supply).

Ant pests can be repelled or killed. A few ants in the wrong place are not a major concern: repel or deter these ants–they will go elsewhere and likely do no harm. Large ant nests in the middle of the garden are a concern; these ants may be eating young plants and cultivating insect pests. Pest ants should be eliminated before they take over the garden.

A bit of background: there are more than 14,000 species of ants. Each species has its own way of living, colonizing, and feeding. You may have to change up your ant control game plan if one method does not solve the problem. Ants can adapt to control strategies.

Ants live in colonies or nests. Ants have a caste system: a queen, worker ants, solider ants, and male ants. Eggs are laid by the queen. The ant lifecycle moves from egg, to larvae, to pupate, and adult. The ants you see around the entrance to the nest are foragers–they collect food and bring it back to the colony and queen. The ants you actually see comprise about 10 percent of the total colony.

Ants are survivors: the nest is built to protect the queen and the colony. Ant nests can withstand rain and flooding. When the nest is under severe attack, worker ants will carry eggs to a new location to avoid total extermination of the colony.

Control of ants in the garden can range from repelling or deterring them to killing them and eliminating the nest. Here are several organic ant controls:

Repelling Ants

If ants are not a major problem in your garden: repel or deter them. Here’s how:

Ants are repelled by strong smells: grow plants with strong natural odors or volatile oils: peppermint and other mints, garlic, rhubarb, tansy, pennyroyal, and sweet fern. Ants are repelled by these plants.

Ants are deterred by acidy plant substances: lemon juice or hot pepper sprays will send ants away. Mix lemon, hot peppers, or garlic with water in a blender then apply the solution as a spray or drench where ants congregate. A few ants will be killed; the rest will relocate. Other ant repellants include black pepper, cayenne pepper, cinnamon, and chili powder.

• Ants are covered with pheromones–a chemical substance. Ant pheromones leave a trail which allows other ants to follow. Disrupt the pheromone trail by spraying the trail with soap and water, garlic and water, vinegar and water, or a peppermint and water mix. The ants will become confused.

Look for honeydew secreting insects–aphids, scale, mealybugs–and get rid of them. Ants farm these insects for the sugar rich honeydew they excrete. If the ants’ food source disappears, the ants will move on. Aphids, scale, and mealybugs feed on weak or injured plants; keep your garden healthy to avoid weak or sick plants.

Killing Ants

If the ant infestation is great and the survival of the garden is in danger, killing ants may be necessary. Be advised that pest ants will be killed, but so will beneficial insects that get in the way. As well, nearby plants may be injured or killed. Use pesticides with caution and care.

Diatomaceous earth is an ant repellant and killer. Diatomaceous earth is crushed sea life fossils. Shards of diatomaceous earth–many of which are nearly microscopic–will cut into soft-bellied insects such as ants, slugs, and cockroaches. The cuts cause these insects to dehydrate and die. Place diatomaceous earth along ant trails and around ant nest entrances.

Boiling water will scald and kill ants. Pour boiling water directly into the entrance to the ant nest. Ant nests can be deep and they are constructed to protect the queen from rain or flooding, so several applications of boiling water may be necessary. Pour 3 gallons of boiling water into the nest each day for several days in a row. Monitor the activity around the nest each day to determine if this has been effective. The best time to treat ant nests with boiling water is mid-morning when ants are most active. You must kill the queen to eradicate the nest. Be advised that boiling water will harm and can kill beneficial insects and nearby plants as well.

Boric acid is a natural occurring compound used as an insect repellant and pesticide. Boric acid–from boron–is poisonous if ingested in large quantities; it is a stomach poison. Be advised that boric acid can harm and kill animals as well as insects if ingested (the amount of harm depends upon the amount ingested and the size of the insect or animal): keep boric acid out of the reach of children and pets: use bait stations that children and pets can not enter. Wash your hands and gloves after working with boric acid.

Make boric acid ant bait by dissolving 1 teaspoon (5 mL) of powdered boric acid and 10 teaspoons (50 mL) sugar into 2 cups (500 mL) of water. Soak cotton balls with this mixture and place them in a bait station near the ant nest or along the ant trail. Worker ants will take eat the bait and carry it back to the nest and queen as food. A bait station should be pet and child proof: place the cotton balls in a jar with a screw top, wrap adhesive tape around the lid locking it, then pierce the jar top several times so that ants can enter and feed.

Boric acid works through dehydration–in the ant’s stomach. Ants can not build up immunity to boric acid.

If you find many dead ants near the bait station, the bait mix may be too strong. The mix should be slow working so that the worker ants carry the bait back to the nest where other members of the colony will feed on it.

Ants can drink from a boric acid-sugar mix, but the bait station should be spill proof so that children and pets do not upset it or drink from it.

Ants do change up their food sources from sugars to carbohydrates: instead of using sugar, you can mix the boric acid with peanut butter. But the bait station must be child and pet proof.

Place sticky glue boards around the nest or trail area to monitor the success of your effort. If few ants are caught in the traps, you effort has worked.

Keep boric acid away from children and pets. Do not get boric acid in your eyes or nose; wash your hands and gloves after using boric acid.

Commercial ant baits with abamectin can be used for heavy ant infestations. Abamectin is an insecticidal compound made in laboratories from the natural fermentation of soil bacterium. Follow the directions.


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    • Ants are often attracted to the garden by pest insects whose excrement contains sugar. Ants particularly like aphids; ants will move the aphids from plant to plant; the aphids suck plant juices and excrete “honeydew” which the ants digest for nutrients. Late in the summer season ants may also be attracted to melons and other crops that grow sweet towards harvest.

  1. I have small caramel colored and attacking beets and potatoes. I live in western Washington state. I have tried diatomacious earth and also boric acid and cotton balls all to no avail. They seem to go away until after the next watering is done. What now?

    • There is likely a substantial ant nest nearby. You have tried organic methods; you can try a chemical bait that ants will take back to the nest. You can also dig to find the nest and attempt to remove and destroy it. In the meantime, you may want to plant your crops in a new spot until.

  2. Found some ants on my watermelon plants so I sprinkled some Diamactuous Earth (cause I had some for my snake’s enclosure) Seemed to be working!

  3. some ant are my long bean it is yet to be ready for harvest . I don’t know how to stop them from eating and I cant remove my the long beans as it kill the harvest. what can i do

  4. Thank you for this information. I was getting ready to plant my perennial Speedwell where my little lilac twig had been and died. When I dug up, there was several 100 red ants and after reading this, I am NOT going to plant it there. The hot weather or the ants killed the lilac so I will plant a little further away and put diatomaceous earth (DE) around the Speedwell plant. I have spearmint and peppermint planted, but not sure how close it has to be to the ants to deter them. Mine are 5 – 10 feet away. Hopeing the ants will stay in their own home and not move onto the other flowers and herbs I have. Thanks

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