The appearance of raised tunnels and scattered dirt mounds across a lawn or garden is often the first sign of unwelcome subterranean activity. These telltale marks are the work of either moles or voles, two common burrowing pests that can cause extensive damage to turf and plant roots. Homeowners seeking an environmentally conscious solution often turn to castor oil, a natural repellent derived from the castor bean plant, Ricinus communis. This method focuses on humanely driving the animals away by making their environment unappealing. Castor oil is a popular choice for controlling these pests because it is generally considered safe for use around children, pets, and desirable plants.
Moles vs. Voles: Identifying Your Target
Successfully treating an infestation begins with correctly identifying the culprit, as moles and voles have distinctly different behaviors and diets. Moles are insectivores, meaning their diet consists primarily of earthworms, grubs, and other soil-dwelling insects. Their tunneling is focused on foraging for this food, and they rarely eat plant material. Mole activity is characterized by volcano-shaped hills of soil (molehills) and raised ridges across the lawn that indicate shallow feeding tunnels.
Voles, on the other hand, are rodents and strict vegetarians that feed on plant roots, bulbs, and stems. They are the primary cause of damage to garden vegetables and flower beds. Vole activity is identified by open, golf ball-sized entrance holes and surface runways—well-worn paths through the grass or mulch. Knowing the difference is important because the castor oil application must penetrate the specific areas where each pest is active.
How Castor Oil Drives Pests Away
The effectiveness of castor oil as a repellent stems from its active component, ricinoleic acid, which imparts a strong, bitter taste and potent scent. Castor oil is not a poison; it is a sensory irritant that makes the soil environment intolerable for burrowing animals. When applied, the solution saturates the soil and contaminates the entire network of tunnels.
For moles, the oil coats primary food sources like earthworms and grubs, making them unpalatable and causing digestive upset. The foul scent and taste signal that the foraging ground is no longer productive, forcing the mole to seek food elsewhere. Voles are similarly repelled, as the oil’s odor makes their underground environment unpleasant and taints the taste of the roots and bulbs they feed upon. The goal is humane relocation, encouraging the pests to move off the property in search of a clean habitat.
Preparing and Applying the Castor Oil Solution
The most effective way to use castor oil is by creating a liquid emulsion that can be thoroughly soaked into the soil. The standard recipe involves mixing six ounces of 100 percent unrefined castor oil with two tablespoons of liquid dish soap. The dish soap acts as an emulsifier, allowing the oil to mix with water and ensuring it penetrates the soil deeply instead of pooling on the surface. This concentrate is then diluted further by mixing it with one gallon of water for application.
The liquid solution can be applied using a standard watering can or a hose-end garden sprayer. Before application, lightly water the lawn to help the repellent soak in more effectively. Apply the mixture liberally, ensuring the soil is thoroughly saturated over all active mole mounds and vole runways.
After the initial application, water the treated area with at least half an inch of water (about ten minutes) to push the oil deep into the tunnels. This ensures the oil reaches the deepest parts of the mole tunnels and fully permeates the soil around vole feeding areas. When using a sprayer, avoid getting the concentrated oil mixture directly on plant leaves, as the oil combined with intense sunlight can cause phytotoxicity. Applying the solution in the late afternoon or on a cloudy day minimizes this risk.
Granular Options
Alternatively, pre-made granular repellents containing castor oil are available. These granules are spread across the affected area using a broadcast spreader and then watered heavily to release the oil into the ground. For the best results, treat the entire infested area and extend the application several feet beyond the activity. This creates a buffer zone that discourages the pests from shifting their territory.
Maintaining the Barrier and Encouraging Relocation
Controlling burrowing pests requires maintaining the castor oil barrier to encourage permanent relocation. The most active times for moles and voles are typically early spring and fall, making these periods ideal for starting treatment. Voles can be destructive in the late fall as they seek winter cover, so an October application is often recommended to protect bulbs and roots.
Initial treatments should be persistent, with reapplication every seven to ten days if new activity is visible. The oil’s effectiveness diminishes over time as it is broken down by soil microbes or washed away by rain and irrigation. A schedule of reapplying every two to three months is necessary for ongoing maintenance, and always reapply immediately following significant rainfall to restore the barrier.
The application technique should strategically drive the pests off the property rather than trapping them in place. Begin by treating undisturbed areas and gradually work toward the property line or a wooded area where the animals can safely relocate. Once the pests have been pushed out, maintain a ten-foot perimeter band of treated soil along the boundary to prevent their return. Monitoring for new mole mounds or vole runways is the best way to gauge success and determine when a follow-up application is required.