Voles are small, stocky rodents, often mistaken for common house mice or even moles, distinguished by their short tails, small eyes, and partially hidden ears. As herbivores, they can cause significant damage in gardens by feeding on plants, especially underground storage organs like roots, tubers, and bulbs. This article clarifies the relationship between voles and onion plants, offering gardeners a guide to identifying damage and implementing effective protection measures.
Vole Dietary Preferences and Onion Consumption
Voles are herbivorous, and their diet consists mainly of grasses, herbaceous plants, roots, and bulbs. They are particularly attracted to these high-energy storage organs, especially during colder months when above-ground foliage becomes scarce. This preference places many garden crops, including onions, at risk of being consumed from below the soil surface.
While voles frequently target bulbs, onions (part of the Allium genus) are considered a low-preference food source compared to non-pungent bulbs like tulips or crocus. This avoidance is due to the sulfur-containing compounds that give onions their distinct, pungent flavor. However, if their population density is high or preferred food sources are exhausted, voles will still resort to eating onion bulbs and roots. The green tops of the onion plant are almost never consumed, as the damage is focused on the bulb and root system underground.
How to Identify Vole Damage in the Garden
Identifying vole damage is crucial and requires looking for signs that differentiate them from other garden pests. Voles create shallow, above-ground runways that are approximately one to two inches wide, which they use for travel between feeding sites. These runways are often hidden beneath layers of dense mulch, groundcover, or long grass.
The entrances to their burrows are small, neat, circular holes which lead to their underground tunnel systems. If you walk across an area with extensive vole tunnels, the ground may feel spongy or soft underfoot. The most definitive sign of damage to the onion bulb itself is the presence of small, clean-cut gnaw marks. These marks are characteristically small grooves, roughly 1/8 inch wide, left by their incisor teeth.
Vole damage is distinct from the activities of moles, which are insectivores that primarily feed on grubs and earthworms. Moles create raised, volcano-like mounds of soil and surface ridges as they tunnel for food, but they do not eat plants. Voles, however, may sometimes utilize existing mole tunnels to access plant roots and bulbs, which can lead to moles being incorrectly blamed for the plant damage.
Strategies for Protecting Onion Plants
Protecting onion plants involves a combination of cultural practices and physical barriers to make the garden less hospitable. Removing heavy layers of mulch, weeds, and dense groundcover near garden beds eliminates the protective cover that voles rely on for safe travel and nesting. Maintaining a short lawn and creating a weed-free buffer strip around the garden perimeter can also discourage their presence.
Physical exclusion is one of the most reliable methods for protecting individual plants and bulbs. When planting, bulbs can be placed within a cage constructed of 1/4-inch hardware cloth or wire mesh. This barrier should extend both above and below the soil line, with the mesh buried six to ten inches deep to prevent the voles from burrowing underneath to access the bulb.
Castor oil solutions can be applied directly to the soil in affected areas, as the smell and taste are highly unpleasant to voles. Predator scents, such as commercially available coyote or fox urine, can also be strategically placed to signal a threat and encourage the rodents to relocate. These methods aim to disrupt the vole’s environment, prompting them to move elsewhere for food and shelter.