Topic for August 2010
Hostas and Voles
Provided by the Western
Massachusetts Master Gardener Association
By Bruce Aune,
If you live in our valley and love hosta lilies, voles are one of your worst
enemies. You might think that slugs deserve this description, because they
riddle the leaves of hostas and some-times sever their stalks, but voles do more
serious damage: they devour hosta roots and often utterly destroy the plant. My
wife Anne and I have fought voles for years, but we have recently hit upon a
simple method of protecting our hostas from them, which has worked very well for
us. I describe it here.
Before offering details about our method, I should first explain what a vole is. They are rodents often confused with mice and sometimes even confused with moles, but they are actually quite different from either animal. In fact, their closest relative in our part of the country is the muskrat; in the far north it is the lemming. They are similar to mice in being small rodents, but where mice have long tales and pink ears, voles have very short tails and small, inconspicuous ears. Of the four species of voles in the eastern U.S., the one that is a scourge to our hostas is the Pine or “Woodland” Vole (Microtus pineto-rum), which is not restricted to pine forests. This vole, pictured at the beginning of this article, is sometimes confused with a mole because it spends most of its life below ground, digging tunnels and living in them, but it is otherwise as different from a mole as it is from a mouse. Moles are blind, have oversized forefeet, and lack the chisel-shaped front incisors of a rodent; voles have bright, beady eyes, typical rodent teeth, and feet that are appropriate to a rodent. Also, where moles feed almost exclusively on grubs or other insects, voles are mainly herbivorous, consuming mostly roots, seeds, fruit, and fungi. As vegetable eaters, they are entirely capable of devour-ing all of a hosta’s roots, leaving its stalks and attached leaves leaning out of an empty hole. I have observed this many times.
Unlike the Meadow vole (Microtus pennsylvanicus), which can often be seen in grasslands or grassy orchards, the Pine vole does not use surface runways but stays for the most part in its underground tunnels. For this reason, they are, as the Massachusetts Audubon Society says, “rarely seen by the non-specialist.” They do occasionally come above ground to gather birdseed fallen from feeders or to move to new areas, but they mostly remain in their tunnels, which compose a winding network just a few inches below the soil surface. The network can be quite large; I have read that in orchards a vole colony’s network can cover the area within the drip line of a mature apple tree. The number of voles in a colony can be quite large: as many as 300 have been re-ported in an acre of a New York apple orchard. Voles do not live long, only about 18 months, but they reproduce rapidly. They be-gan to bear young at two months, and they may produce five or six litters of one to five young in their reproductive life. If you do the math, you will see that a pair of voles can give rise to a large population in their short lifetime.
Because Pine voles spend most of their life under ground, they are difficult to trap. Some people attempt to control them by using poison bait, but this can be harmful to the many predators that prey upon them, which include birds (hawks and owls) as well as well as snakes and mammals such as skunks, weasels, raccoons, and foxes. Our method of control is to plant our hostas in underground fences (we call them cages) made from hardware cloth with one-quarter inch mesh. This is an obvious method to use, but the cages we make are a little special. They don’t call attention to themselves.
Hardware cloth, a metal ”fabric,”, can be quite expensive if you buy it in ready-made rolls; it is cheaper to get it from a lumberyard where it is sold in bulk. But however you buy it, it will be too wide to use without cutting into strips. Because the tunnels of Pine voles are fairly close to the surface, the cages you make need only extend about eight inches below the ground. This depth has proved to be satisfactory for us. But Pine voles do sometimes emerge from their burrows to look for food or new territory, so it is wise to have your cages extend above the ground as well. We have found that three inches above the ground is sufficient, at least if the top of the cage is left spiky and sharp. Voles, we suppose, have tender feet, and they are not inclined to climb over a spiky obstacle.
To obtain the eleven-inch strip of hardware cloth needed for your protective cage, you will have to cut the hardware cloth. It is rewarding to use good-sized tin snips for this purpose: smaller ones will do, but large ones make the task quick and easy. We have found that small plastic cable-ties (the kind used by electricians) make neat and unobtrusive connectors. Make your strip of hardware cloth as long as you need for a cage of the size you want. If your hosta is small, you will want a small cage; if you are planting a larger one, such as a Sum and Sub-stance hosta, and you are not planning to move it in the near future, you will want a large cage and therefore a long strip of hardware cloth. It is worth noting that if you aim to move a large plant, it is helpful to leave its cage in place: the roots are held together by the cage, which provides a useful handle for moving the plant about. Hosta roots that have grown through the cage are easily extricated if you want to put the plant in a larger cage. Just be careful in pulling them out. A new hole can then be dug, a new cage made, and the hosta can be planted again.
A final point: the three inch-tops of an unadorned hardware cage are bright silver and call unwanted attention to them-selves. The solution is to spray-paint them in an unobtrusive color. We have found that brown automobile primer is a good choice for this. When we use it, the cage tops are inconspicu-ous. The cages provide the need protection, but they do not de-tract from the beauty of the plants. We have used cages for about four years now, and I am glad to say that we have yet to experience a casualty from predatory voles.
Below is a picture of a young Hosta ‘Halcyon’ with its in-conspicuous brown cage; the cage is barely visible at the bottom of the picture.
Hosta 'Halycon' with cage
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Provided by the Western
Massachusetts Master Gardener Association