Installing underground barriers is often more effective at reducing crop damage over the long run than pursuing ongoing, lethal methods. Galvanized wire mesh, commonly known as hardware cloth, is a good material to use – the holes are small enough that even the tiniest shrew can’t get through, and it lasts for decades. There are several ways to use it in the garden.
Use hardware cloth baskets to protect the roots of individual plants. This method is feasible only at planting time and is mainly used for shrubs and trees. The basket should be at least the size of the root ball at planting time, but bigger is better. The roots will grow through the holes of the hardware cloth over time, but even if those get nibbled off, the core of the roots remains protected and the plant will survive. You can either buy a roll of hardware cloth and fold it into baskets yourself (make sure the seams are well-overlapped) or splurge on pre-fabricated baskets.
Line beds with hardware cloth. This method has to be done prior to planting and is used to protect large areas containing many plants. It is the most common method used for vegetable gardens. For raised beds with wooden sides, put a layer of hardware cloth at the bottom of the bed before filling it with soil and staple it to the wood so the critters don’t weasel their way in on the sides. To protect beds on the ground, remove the soil to a depth of at least 12 inches and then line the entire area with hardware cloth. The hardware cloth should extend at least 12 inches aboveground as well to keep the animals from going up and over. Always overlap multiple pieces by 6 inches and bind them together with bailing wire to create a solid barrier.
Install an underground fence. For areas that have already been planted, but don’t yet have a problem with underground pests, a vertical hardware cloth ‘fence’ can keep them from getting their foot in the door. Dig a trench at least 2 feet deep around the periphery of the garden area and place the hardware cloth on one edge. Fold the bottom of the hardware cloth at a 90-degree angle (facing away from the area to be protected) to create a horizontal surface at least 6 inches wide at the bottom of the trench to deter animals that try to tunnel down and around. The fence should also extend 12 inches aboveground.
If exclusionary methods sound too labor-intensive, there are a slew of repellents to experiment with. Some are homemade, some are commercially available, but none are guaranteed to be effective. Yet many gardeners swear by them, so it may be worth a bit of trial and error to find one that is effective in your situation.
Human Hair. Collect it fresh from the barber or a beauty school and place it in actively used tunnels. Most underground critters are said to detest the smell (or at least associate it with a potential predator). Dryer sheets, coffee grounds and garlic powder are among the many scented household products are thought to drive them away.
Audible Repellents. Putting a battery powered radio in a sealable plastic bag, tuning it to an all-talk station and leaving it in a tunnel for a week or so may scare the animals away. There are also ‘sonic spikes,’ electronic devices that emit a high frequency sound that makes life very unpleasant for underground animals.
Granular Repellents. Most all-natural commercial repellents use castor oil as the active ingredient. Start spreading the granules at one end of the garden and work your way across, covering another 15-foot swath each day in order to ‘herd’ the animals out with the repulsive smell of the product.
Plant Repellent. Gopher purge (Euphorbia lathyrus) contains alkaloids in its roots that are extremely distasteful, especially to gophers. Surrounding the garden with a hedge of this low-growing species is a way to create an underground barrier without all the digging.
All underground animals have important ecological roles to play, so one option is to learn to coexist and benefit from their presence. They improve drainage by loosening the soil, some prey on grubs and other garden pests, and they slowly enrich the earth with their manure. Like any pest, there are natural predators that keep populations of burrowing animals in check over the long term. Brush piles and large rocks provide habitat for snakes, one of the most common predators of subterranean mammals. Installing owl boxes on your property encourages these stealthy airborne rodent predators, especially to control species like voles that venture aboveground at night.
Relying completely on predators for pest control will never eliminate every last animal, but it can keep their populations from booming. Mature fruit trees, berry bushes, fruiting vines and perennial herbs are rarely damaged by small populations of burrowing animals, so diversifying the landscape with these plants – and encouraging predators – is one way to garden in greater ecological harmony.