Ants are common on plants, both indoors and in the garden, and their presence often concerns plant owners. While ants rarely cause direct harm, their activity indicates a deeper issue. The goal is deterrence, using non-toxic and practical methods that maintain a healthy growing environment. Understanding the true reason for the ants’ presence allows for targeted strategies to keep them away from valuable plants.
Why Ants Are On Plants
Ants are not on plants to consume foliage; they are there for a desirable food source produced by other insects. This food is “honeydew,” a sugary, sticky liquid excreted by sap-sucking pests, primarily aphids and scale insects. These pests feed on the plant’s phloem sap and must expel the excess sugar as waste.
This interaction forms a mutualistic relationship, sometimes called ant “farming.” The ants actively guard these honeydew-producing pests from natural predators, such as lady beetles and parasitic wasps. They may even stroke the pests with their antennae to stimulate honeydew release and move their “herds” to nutrient-rich parts of the plant.
Creating Physical Barriers
Creating a physical obstruction that ants cannot cross is an immediate and effective method for deterrence. Ants rely on continuous surface contact to travel, making sticky materials useful. Commercial products like Tanglefoot or petroleum jelly can be applied as a band around a tree trunk or the rim of a potted plant.
When applying a sticky barrier to a live stem, first wrap the area with a non-porous material, such as duct tape, to prevent bark damage. For potted plants, a simple water moat works by placing the pot inside a shallow tray filled with water. The water barrier must be maintained and kept free of debris that could form a bridge.
Diatomaceous Earth
Food-grade diatomaceous earth (DE) is another effective physical barrier. This fine powder is made from the fossilized remains of microscopic aquatic organisms. DE acts as a mechanical insecticide because its tiny, sharp silica particles scratch the ant’s waxy outer layer, causing abrasions. This damage leads to desiccation, where the ant rapidly loses internal moisture and dies from dehydration. To remain effective, the powder must be applied as a thin, dry barrier around the base of the plant or container, as moisture renders it inert.
Using Natural Repellents
Natural substances use potent scents to disrupt the chemical communication system ants rely on for navigation. Ants use pheromone trails to mark paths to food sources, and strong odors can overwhelm or mask these signals. This disruption confuses foraging ants, preventing them from locating the plants.
Essential Oils and Sprays
Peppermint essential oil is effective because its active compounds, including menthol, act as a natural irritant that scrambles ant navigation. A simple spray is made by mixing 10 to 20 drops of oil with water and a small amount of dish soap for emulsification. This solution can be sprayed along ant trails or around the container perimeter, but avoid spraying foliage directly to prevent burning.
Powdered Spices and Vinegar
Powdered spices like cinnamon and cayenne pepper also work as olfactory deterrents. Cinnamon contains trans-cinnamaldehyde, which repels ants by masking their pheromone trails. Spreading a thin line of cinnamon or chili powder directly on the ground creates a temporary barrier. Similarly, a solution of white vinegar and water, typically mixed in equal parts, can be sprayed directly onto trails to instantly break down the chemical signals ants use to follow one another.
Eliminating Primary Pests
The most sustainable strategy involves removing the source of attraction: the honeydew-producing insects. Once these primary pests are eliminated, ants will seek food elsewhere. The fastest initial control method is physically dislodging the pests with a strong, focused blast of water from a hose.
Topical Treatments
For persistent infestations, a solution of insecticidal soap or neem oil can be applied directly to the pests. Insecticidal soap is effective against soft-bodied insects like aphids and scale because it works on contact, dissolving their protective outer layer. Neem oil, derived from the neem tree, works as a repellent, an anti-feedant, and disrupts the pests’ growth cycle.
Biological Control
Introducing beneficial insects is a long-term biological control method that provides ongoing protection. Predators such as ladybugs, green lacewings, and hoverfly larvae naturally seek out and consume aphids and scale. By applying soap or neem oil only to the infested areas, the presence of these beneficial insects can be encouraged, providing a natural defense against future pest outbreaks.