Some of the most common questions posed to Marin Master Gardeners via the help desk and at the various Marin farmer's markets are what to do about the damage being done to gardens and turfs by gophers, moles and voles.
First, we need to identify the unwanted underground visitor that has made itself at home at your garden. Once we know what the furry invader is, the question then is how to get rid of them.
Know the invader
The gopher: Gophers are herbivorous, burrowing rodents. Although they are sometimes seen pushing dirt out of a burrow, gophers mostly remain underground in a tunnel network that is usually 6 to 12 inches below the surface. The best sign of gopher presence are mounds of fresh soil. The mounds are formed as the gopher digs its tunnel and pushes the loose dirt to the surface. The mounds usually appear crescent or horseshoe-shaped. The hole is usually off to one side and is plugged.
Gophers feed on a variety of vegetation but usually prefer herbaceous plants, bulbs, shrubs and trees. They generally stay underground to feed on roots and fleshy parts of plants, but they sometimes feed aboveground and will leave a tell-tale circular band of clipped vegetation around the hole. Gophers can pull an entire plant into their tunnel from below, and they can also gnaw and damage plastic water lines and sprinkler systems. Their tunnels can divert irrigation water.
The mole: The small, insect-eating mammal is not part of the rodent family. Moles live almost entirely underground in a vast network of interconnecting tunnels. Moles commonly burrow just beneath the surface where their favorite worms, insects and other invertebrates live.
Mole mounds appear circular and have a plug in the middle that may not be distinct and have a volcano-shaped profile. The surface feeding burrows appear as ridges that the mole pushes up as it forces its way through the soil. All this burrowing can dislodge plants that will then cause the plant roots to dry out.
The vole: The small, mouselike rodents spend most of their time in their burrow system below ground, but they do spend time aboveground and sometimes be seen running about. The clear sign that you are being visited by a vole is the presence of well-traveled aboveground runways that connect burrow openings, which can be about 1½ to 2 inches in diameter. A protective layer of grass or other groundcover usually hides the runways.
Voles are mostly herbivorous and feed on a variety of grasses, herbaceous plants, bulbs and tubers. In fall and winter they can eat the bark and roots of trees that can seriously damage the health of a tree.
Measures to eliminate gophers, moles and voles vary and include home remedies, trapping, repellents, natural controls and baiting.
Gophers do not hibernate and are active all year long. They generally live alone within their burrow system except when breeding or females with young. Their burrow system can cover an area of 200 to 2000 square feet.
Ridding your garden of gophers completely is a virtually impossible task. The most surefire way to protect the roots of vulnerable plants is by placing sturdy chicken wire between your plants and the gopher. I have friends who dug up their entire lawn in Point Reyes, put down wire and then replanted their turf. They also sunk wire baskets into planting holes. I also have seen galvanized bins or wine barrels used for plantings, especially vulnerable ones such as dahlia tubers.
Some gardeners say gophers do not seem to eat such as the gopher plant (Euphorbia lathyrus), catmint, rosemary and lavender. You can try this approach, but persistent gophers will just go around these plants to those they prefer.
Gophers do not frighten easily. Products sold to scare them away like noisemakers, vibrating stakes and wind-powered wheels are ineffective. Think about it, you see gopher mounds by railroad tracks! At this time there is no proven repellent for gophers. Trapping is a safe and effective way to control gophers. Baiting with toxic baits is discouraged because a gopher that dies with toxins in their body can enter the food system of other beneficial creatures. For a thorough explanation of how to effectively trap a gopher, check out the University of California Integrated Pest Management Pest Note on Pocket Gophers at www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7433.html.
As with gophers, trapping is the most reliable method of mole control. The traps suggested for mole control are different than those effective for gophers so, again, you need to know who is disturbing your garden. Check out the UCIPM Pest Note on Moles for more information on dealing with moles at www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74115.html.
If you suspect your visitor is a vole, it is important to start managing the problem quickly because their numbers can increase rapidly. A good way to deter vole populations is to make the habitat less accommodating to them. Cut back on groundcovers, and keep weeds mowed. Keep mulch layers thin and several inches away from the trunks of trees and shrubs. A trench dug around an area you want to protect, about a foot deep and 6 to 8 inches high and filled with gravel or pebbles, can also work. Since voles are aboveground, baiting is discouraged. There is too much worry for the safety of children, pets and animals that are not being targeted. For more information on dealing with voles visit the UC IPM Pest Note on Voles at www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7439.html.