Ridding your yard of voles isn't terribly difficult, but it requires perseverance and vigilance. Voles are short-legged, short-tailed rodents with small eyes and small ears. They have long, coarse fur that is dark brown to gray-brown in color and they grow to lengths of between four and six inches, exclusive of their tails. But don't let their size fool you: These are extremely destructive pests. They chew roots and destroy main stems of plants, effectively killing any plant or tree with which they come in contact. Voles can destroy plants above ground and below ground.
Before moving to rid your yard of voles, ensure that the damage you see is, indeed, cause by voles. Voles have very small teeth, so they leave small, irregular bite marks on the roots or stems; these bite marks will have various angles (unlike rabbits, which will cut the root in two with a regular cut with a 45 degree angle).
You can identify vole burrows by fresh grass clippings and greenish droppings that are about 3/16 of an inch long; as the droppings "age," they turn gray or brown.
Prevention is your best course of attack against voles. You need to manage your yard's vole population before it reaches large numbers. The key is to ensure that you don't support a habitat that is suitable to them. Removing protection like weeds, tall grass, dense vegetation, and heavy mulch will make your yard less attractive of a habitat. Voles do not like open territory, and will use anything they can to hide themselves. Keep grass adjacent to flower beds or gardens mowed short. Minimize the amount of mulch that you use in your garden and turn or replace the mulch frequently to prevent the voles from establishing any tunnel systems.
You can establish a wire fence around your garden to exclude voles entirely. The fence should reach a height of at least 12 inches and should have a mesh size that is 1/4-of-an-inch or smaller. You can use a fence such as them on its own or attach it to the bottom of an existing fence. Go a step further by burying the bottom of the fence into the ground to depths of at least six to ten inches. Extending the fence below ground will prevent the voles from tunneling into your garden. You can increase the efficacy of your fence by establishing a weed-free barrier outside of your fence.
Trapping large numbers of voles is not a reasonable course of action for managing large populations, nor is it cost effective. Trapping is effective, however, if your population is small. For a small garden, you'll likely need a minimum of twelve traps; you may need upwards of 50 for a large garden. Simple mousetraps baited with a mixture of peanut butter and oatmeal or with apple slices will suffice.
Where you place your traps is crucial. Set the traps along their runways, as voles rarely stray from their established routes. Your trap should be at a right angle to the runway, so that the triggered end extends into the path. You should check the traps daily to remove any that have captured voles or to reset them. Continue using the same trap location until you cease to capture voles, at which point you should move the trap 15 to 20 feet away.
Toxic baits can be effective means of killing voles. If you choose to use chemical baits, however, ensure that you keep them away from children and pets and that you read and obey all safety precautions printed on the baits. The safest types of bait to use around your home are anti-coagulants. These baits interfere with the vole's ability to clot blood, a process that is slow-acting but effective. These baits are available at most hardware stores. If you have cats and dogs, however, avoid using products that contain anti-coagulants such as brodifacoum and bromadiolone. Read the product label carefully to ensure that you use it correctly. Voles must feed on such baits for a period of five or more days in order to be effective, so ensure that you leave it out long enough to control the populations; you may have to broadcast the poison every other day for a week or two in order for it to be effective.