Dahlia growers often find their prized tubers damaged or missing, and the immediate suspect is usually the mole due to nearby earth mounds. This widespread assumption links the mole’s visible tunneling activity with the destructive consumption of the plant’s underground storage organs. However, subterranean ecology reveals that the mole is likely not the culprit eating the dahlia, but rather an unwitting accomplice. Understanding the difference between the animals that tunnel and the animals that feed is the first step toward effective tuber protection.
Mole Diet and Tunneling Habits
Moles are classified as insectivores, meaning their diet is based primarily on insects and other small invertebrates. They possess a high-energy metabolism that requires them to consume a significant amount of food daily, often eating between 80% and 100% of their body weight in prey. Earthworms make up the bulk of their diet, supplemented by grubs, centipedes, and insect larvae found in the soil.
The extensive network of tunnels moles create serves as an underground hunting ground. Moles use their acute sense of touch and vibration sensitivity to detect earthworms and insects that fall into these channels. While a mole’s tunneling can certainly disrupt the root systems of plants, they lack the digestive system adapted to consume starchy plant material like dahlia tubers. Moles do not eat the tubers; they only dig past them in pursuit of protein-rich invertebrates.
The True Culprits of Tuber Damage
The animals responsible for consuming dahlia tubers are herbivores, most commonly voles and sometimes gophers. Voles, sometimes called meadow mice, are rodents that feed on plant matter, including stems, roots, and underground storage organs. When a vole attacks a tuber, the damage is characterized by distinct gnaw marks, often resulting in the tuber being partially or completely hollowed out.
Gophers are also herbivores that create their own tunnel systems to consume roots and tubers. The critical link between moles and these pests is the established mole tunnel, which voles frequently utilize as a safe highway to reach food sources. Mole hills alert the gardener to underground activity, but the actual feeding damage is evidence of a small rodent that followed the mole’s path. Mole activity leaves raised ridges of earth, while vole activity leaves chewed-up plant material.
Strategies for Underground Tuber Protection
Protecting dahlia tubers involves creating physical barriers that exclude plant-eating rodents from accessing the food source. One effective method is planting the tubers inside a wire basket, often referred to as a gopher basket or root cage. This barrier should be constructed of galvanized hardware cloth with openings no larger than half an inch to prevent voles from passing through.
Another strategy is to plant the tubers inside nursery pots or containers with the bottom removed. The sides of the pot protect the tuber clump from lateral access, while the open bottom allows the roots to grow down into the soil. Gardeners also amend the soil around the tubers with materials like gravel or sharp sand, which makes the area less appealing for rodents to tunnel through. Since voles often use mole tunnels, managing the mole population by reducing their food sources, such as grubs, can also indirectly reduce the pathways for voles.