Ants are common in gardens, drawn by food, water, and nesting locations. While some species are beneficial by aerating soil or preying on pests, their presence often signals an underlying problem or leads to direct damage to plants. Effective control focuses on eliminating the colony using methods safe for produce, beneficial insects, and the overall garden ecosystem. The goal is to manage the population and remove incentives that make your garden appealing.
Non-Toxic and Physical Removal Methods
Immediate, low-impact methods are best for spot treatments or small infestations near food crops. Pouring boiling water directly into a visible ant mound can kill a significant number of ants, potentially including the queen. However, this method is only about 60% effective because the water cools quickly, and it will kill surrounding vegetation.
A simple, non-toxic contact spray combines liquid dish soap and water. The soap solution penetrates the ant’s waxy exoskeleton, causing rapid dehydration and death. This spray instantly kills foraging ants and disrupts the pheromone trails they use to communicate. For ants climbing plants, a high-pressure jet of water from a hose can physically dislodge them.
To prevent ants from reaching vulnerable plant parts, employ physical barriers. Applying a thin band of petroleum jelly or a sticky tree wrap around the base of a plant stem or pot rim creates a barrier the ants cannot easily cross. These methods provide quick relief but generally do not solve the problem of the entire colony.
Targeted Baiting and Colony Control Agents
Long-term ant control requires eliminating the queen to prevent the creation of new worker ants. This is achieved using slow-acting agents that workers carry back to the nest. Food-based baits, such as a mixture of sugar and a slow-acting stomach poison like boric acid, are highly effective. The sugar attracts the worker ants, who consume the mixture and transport it to feed the queen and larvae.
The toxin concentration must be carefully controlled. If the boric acid is too strong, the worker ant will die before returning to the colony, defeating the purpose of a slow-acting bait. A common ratio involves mixing one to two teaspoons of boric acid into a cup of sugar water to create a palatable poison. Place these baits within secure, inaccessible containers away from pets and children, as boric acid is toxic if ingested.
Another tool for colony control is food-grade Diatomaceous Earth (DE), a fine powder made from the fossilized remains of diatoms. DE is a mechanical insecticide that kills by physical means. The microscopic particles are abrasive and puncture the ant’s waxy outer layer, causing the ant to die from desiccation. For DE to be effective, it must be applied as a light, dry dust barrier around the nest or foraging trails, as it loses its killing properties when wet.
Addressing the Root Problem
Ants are often present in the garden because they are “farming” sap-sucking insects, particularly aphids. This is a mutualistic relationship: aphids feed on plant sap and excrete honeydew, a sugary waste product that serves as a high-value food source for the ants. In return for this honeydew, the ants aggressively protect the aphid colonies from natural predators like ladybugs and lacewings.
The most sustainable way to deter ants is to eliminate their food source by controlling the aphid population. Introducing beneficial insects, such as ladybug larvae or lacewings, is an ecological approach to naturally suppress aphid numbers. These predators quickly consume the slow-moving aphids, removing the ants’ incentive to remain in the area.
For a more direct approach, horticultural oils or insecticidal soaps can treat aphid infestations. Neem oil, a type of horticultural oil, is effective because it suffocates aphids on contact and acts as an insect growth regulator and feeding inhibitor. When using these sprays, ensure you cover the tops and undersides of the leaves where aphids cluster. Apply the product in the early morning or evening to avoid harming pollinators.