How can I protect my plants from voles?

Exclusion can be used to protect highly valued flower beds, gardens, shrubs, and trees from vole damage. Install woven wire or hardware cloth fences (1/4-inch or smaller mesh) around small flower beds or gardens to reduce vole activity. The fence should be about 12 inches high, and the bottom should be buried 2 to 3 inches into the ground. Where pine voles are a problem, the fence should extend about 6 inches below ground. Rabbits and ground squirrels will also be excluded if you make the fence 18 inches tall and bury it into the soil a few inches.

Use 1/4-inch hardware cloth or plastic cylinders to protect individual trees and shrubs. Again, the cylinder should be tight to the ground or buried slightly and should extend higher than the maximum depth of snow in winter, including drifts. The height of the cylinder should be at least 18 inches above the snow depth, if possible, where rabbits are also a potential problem. When making the cylinder, overlap the edges at least 1 inch, and fasten it securely so gaps do not form that could admit voles. Cylinders of galvanized hardware cloth should last about five years, so make them large enough in diameter to accommodate expected trunk growth if they remain in place during the growing season.

Additional information on vole management can be found at:
Voles
Vole publication