Moles are a frequent nuisance for gardeners due to their extensive tunneling activity just beneath the soil surface. Unlike voles, which are rodents that consume plant roots, moles are insectivores, primarily feeding on earthworms, grubs, and other invertebrates. Gardeners often assume that a raised bed provides automatic protection, but moles can easily tunnel up from the native soil below into the richer, softer environment of the bed. Effective mole control relies heavily on proactive prevention strategies, focusing on physical exclusion and making the area unappealing to these subterranean foragers.
Physical Barriers for Exclusion
The most reliable method for protecting a raised bed involves installing a continuous physical barrier at the bed’s base. This barrier must be implemented before the bed is filled with soil, making new construction the ideal time for installation. The recommended material is galvanized hardware cloth with a mesh size of \(1/2\) inch or \(1/4\) inch. This tight weave is small enough to block the passage of an adult mole.
Galvanized material resists rust and corrosion, ensuring the barrier lasts for many years beneath the moist soil. To prevent moles from tunneling around the barrier and up the sides, the mesh must extend vertically up the interior walls of the raised bed. Securing the hardware cloth to the inside framing, ideally to a height of at least six inches, creates an underground basket.
For existing raised beds, retrofitting this barrier requires substantial effort. The bed must be completely emptied of soil, the ground leveled, and the hardware cloth secured to the bottom and sides before the soil is replaced.
When multiple pieces of mesh are required to cover the base, they should overlap by at least six inches and be fastened together with hog rings or wire ties to eliminate gaps. If the hardware cloth is not secured to the sides, moles can exploit the seam where the mesh meets the bed frame.
Applying Repellent Methods
Once a raised bed is established, non-lethal repellents can be used to discourage moles from entering the area. Castor oil is a widely utilized option because it does not harm the moles, but it contaminates their food source and irritates their digestive system.
Castor oil is applied as an emulsion, mixed with a small amount of liquid detergent to help it penetrate the soil when diluted with water. Commercial liquid products or a homemade mixture can be drenched into the soil of the raised bed and the surrounding perimeter. This treatment should be applied liberally to ensure the oil soaks deep into the soil where the moles forage.
Granular castor oil products are available, although they may be less effective than liquid drenches because they do not penetrate the soil as deeply or consistently. Another repellent approach involves using devices that emit vibrations or sonic pulses into the ground. These spikes disrupt the moles’ sensitive hearing and touch receptors, making their habitat uncomfortable.
The effectiveness of these sonic or vibrational devices is variable, depending on the soil type, conditions, and depth of placement. To maximize their potential, the spikes should be buried approximately twelve inches deep to ensure vibrations travel effectively. These repellents should be used as a supplement to physical barriers or as a way to herd moles out of the immediate vicinity.
Addressing Moles in Surrounding Areas
Moles in a raised bed almost always originate from the surrounding lawn or garden areas, where they establish their primary tunnel systems. Managing the population in these adjacent zones reduces the pressure on the protected raised bed. One strategy is to target their food source, specifically beetle grubs, which are a major component of a mole’s diet.
Applying beneficial nematodes or milky spore disease to the lawn helps control the grub population, making the area less attractive to moles. Moles also feed heavily on earthworms, so eliminating grubs alone may not completely solve an infestation. However, reducing one primary food source can encourage moles to move on to other territories.
Regularly collapsing the visible surface tunnels and mounds in the surrounding yard is a simple tactic that disrupts the moles’ routine. Moles expend significant energy to maintain their tunnel networks, and having to repeatedly repair them is a deterrent. This constant disturbance, combined with a physical barrier on the raised bed, provides a multi-layered defense.