Deer, rabbits, mice, voles, and other animals can cause a lot of damage to trees and shrubs over the winter months. Prevention is key to managing these garden pests. By taking steps in the fall, you can prevent damage from occurring over the winter.
These animals may feed on trees and shrubs during winter and severely damage or destroy plants. Damage is most likely to occur when food is scarce during prolonged periods of snow cover. Mice and rabbits may girdle the trunks of small trees, effectively destroying them. Deer may devour the foliage on the lower branches of arborvitae, pines, and other evergreens. In fall, bucks rub their antlers on trees to remove the dried velvet from their antlers and to mark their territory. This rubbing removes the thin layer of bark on small trees and can seriously damage or destroy them.
Below is how to help manage these critters and prevent damage to your garden plants through the winter months.
Trees and Shrubs Susceptible to Damage
Trees and shrubs that are often damaged by rabbits in winter include crabapple, apple, pear, redbud, honey locust, serviceberry, burning bush (aka winged euonymus), flowering quince, barberry, roses, and raspberries. Small evergreens (especially pines) are also vulnerable. However, nearly all small trees and shrubs are susceptible to damage when food sources are scarce, and rabbit populations are high.
Type of Damage
Rabbits feed on the tissue between the bark and the wood. If rabbits remove the tissue down to the wood and go completely around the tree's trunk, the damaged tree is effectively girdled. Girdling destroys the tree by disrupting the downward flow of food from the tree's foliage to the root system. Rabbits damage shrubs by chewing off small branches and girdling large stems.
Placing chicken wire or hardware cloth fencing around vulnerable plants is the most effective way to prevent rabbit damage to trees and shrubs in the home landscape. To adequately protect plants, the fencing material needs to be high enough that rabbits won’t be able to climb or reach over the fence after heavy snow. In most cases, a fence that stands 24 to 36 inches tall should be sufficient. To prevent rabbits from crawling underneath the fencing, pin the fencing to the soil with U-shaped anchor pins.
Small trees can also be protected by placing white corrugated or spiral tree guards around their trunks. After a heavy snow, check protected plants to make sure rabbits aren’t able to reach or climb over the fencing or tree guards. Remove some of the snow to keep rabbits from reaching the trees or shrubs if necessary.
Damage may also be reduced by removing brush, junk piles, and other places where rabbits live and hide. Repellents are another option. Repellents discourage rabbit browsing because of their unpleasant taste or smell. Unfortunately, repellents aren't always effective and can be difficult to apply in the winter months when temperatures are below freezing. They need to be reapplied after heavy rain or snow. It may also be helpful to reduce the rabbit population in the area by removing some of the rabbits with live traps.
On many trees and shrubs, rabbits remove the bark completely around the trunks and stems, effectively girdling them. All growth above the girdled areas will eventually die, and for most home gardeners, replacing the girdled trees is the best course of action. There are no applications that will mitigate the effects of rabbit damage or save severely damaged trees. Wound dressings, pruning paints, latex paints, wrappings, and other alleged protective barriers do not help.
Most deciduous shrubs can produce new shoots or suckers at their base. Because of this ability, many severely damaged deciduous shrubs will eventually recover. Several years may be required for some shrubs to fully recover. In early spring, prune off girdled stems just below the damaged areas.
What about bridge grafting? Some girdled trees can be saved by bridge grafting. However, bridge grafting is a difficult procedure for home gardeners. Most girdled trees will sucker at their base, and since most fruit and ornamental trees are produced by grafting, suckers that originate from below the graft union will not produce a desirable tree. Instructions on bridge grafting are available in this article from Michigan State University: Bridge grafting as a life-saving procedure for trees.
Preventing Deer Browsing
Deer may feed on trees and shrubs during winter and severely damage or destroy plants. Damage is most likely to occur when food is scarce during prolonged periods of snow cover. Deer often feed on the foliage on the lower branches of arborvitae, pines, and other evergreens but also feed on other plants, especially when food is scarce. Prevention is key to managing this damage.
Tree Guards, Tubes, & Wire Cylinders
Tubes, wraps, wire fencing, and wire cylinders can be placed seasonally around individual trees and shrubs to physically exclude and prevent deer from browsing. When placed early in the fall, they are also often effective at preventing damage from antler rubbing. Guards, tubes, and cylinders are not permanent structures and need to be removed in spring. They are most effective on smaller, younger plants that are more susceptible to significant damage from deer feeding. These structures should be at least six feet tall. Wire cylinders can be shorter for smaller plants if they are closed on top.
Exclusion with fencing materials is the most effective - albeit often the most costly - method to prevent deer from eating and otherwise damaging garden plants. Fencing can be permanent for year-round protection or temporarily installed in the fall to prevent damage during the winter months. Woven wire or mesh fences are good options as they are durable, flexible, and easy to install across a variety of terrains. To protect an entire garden area, fences must be at least 8 feet tall. If the area that needs to be protected is smaller than 8 feet by 16 feet, a shorter fence of 50 inches can be used to exclude deer since deer will not jump into a small, fenced enclosure.
Electric fencing made from electrical wire or polytape can be used to deter deer from entering a garden area. Deer must be trained to avoid the fence by baiting it with peanut butter spread on aluminum foil and folded over the wires. The light shock that comes when they sample the bait will deter them from coming near the fenced area. Flags or bright-colored polytape help make the fence more visible to deer and people in the area. Check local regulations before installing an electric fence, as they may be prohibited in your area.
Fishing line can be used as a simple and visually unobtrusive way to deter deer from entering a garden area. String high-test (30 lb. +) monofilament fishing line tightly around a garden bed at least two feet beyond the outside edge and 36 inches above the ground. Deer encounter the fishing line in the dark, making them uncomfortable and avoiding the area. Inspect the line often for breakage. This method works on a short-term basis and for areas that have low deer density. It is not effective for areas that see daytime feeding where deer can see the fishing line.
Repellents can provide short-term protection for smaller garden areas. Repellents work in one of two ways - as a contact repellent, like capsaicin, applied directly to the plant to make it taste unpleasant, or as an area repellent, like predator urine, that deters deer because of an unpleasant odor. Change the scents and types of repellents regularly to prevent deer from getting used to the scent and ignoring it.
Apply repellents early and often when conditions are dry and temperatures are above freezing. Apply sprays from a height of 6 feet down since deer typically browse from the top down. Over the winter months, repellents have limited success at preventing deer browsing because reapplication can be difficult in freezing temperatures.
Changing the garden to make it less attractive to deer can help reduce browsing damage. Plant highly desirable plants in areas with more human activity. Utilize more deer-resistant plants near garden edges or places where deer are more likely to browse, such as near wood lots. Never feed deer in your area. While this management approach is not very effective on its own, it can help when combined with other management techniques.
In fall, bucks rub their antlers on trees to remove the dried velvet from their antlers and to mark their territory. This rubbing removes the thin layer of bark on small trees and can seriously damage or destroy them as it disrupts the water and nutrient-conducting tissues in the tree. Young trees with flexible trunks and thin, smooth bark are most likely to be damaged. Once trees have more corky and thick bark with trunks that are not flexible (usually when they are 3 to 4 inches in diameter or larger), the chance of damage from antler rubbing goes down significantly. Trunk damage typically occurs 1½ to 3½ feet above the ground.
Preventing Antler Rubbing Damage
Damage caused by bucks rubbing their antlers on small trees can be prevented by utilizing one of a few exclusion methods. The barriers must be in place by mid-August to avoid damage from antler rubbing and should be removed in the spring to prevent possible interference with growing trees.
One of the easiest and least labor-intensive methods is to drive three sturdy metal or wooden stakes around the young tree. The space between the posts should not be more than 18 inches.
Tubes, wraps, wire fencing, and wire cylinders can also be placed seasonally around individual trees. The fencing material must be sturdy (such as steel welded wire fencing). These structures should be at least six feet tall. Wire cylinders can be shorter for smaller plants if they are closed on top.
How to Manage Deer Damage If It Occurs
Browsing on Evergreen Trees and Shrubs
Evergreens are regularly damaged by feeding deer over the winter. Arborvitae and yews are most susceptible to browsing by deer in winter.
The extent of damage to the lower portions of the arborvitae will be determined by the presence or absence of buds (growing points). If buds are present, the lower branches will produce new growth in spring. The new growth should be apparent by early summer. The lower portions of the arborvitae will remain bare and likely never develop new growth if no buds are present.
Browsing on Deciduous Trees and Shrubs
On many trees and shrubs, deer will browse branch tips and stems. Heavily damaged trees may need to be replaced, but if only secondary branches are lightly browsed, the tree will recover. Most deciduous shrubs can produce new shoots or suckers at their base. Because of this ability, many severely damaged deciduous shrubs will eventually recover. Several years may be required for some shrubs to fully recover.
Damage from Antler Rubbing
The process of rubbing removes bark. If the bark is removed on a large portion of the tree or completely around the trunk, the tree becomes girdled. All growth above the girdled areas will eventually die, and for most home gardeners, replacing the girdled trees is the best course of action. There are no applications that will mitigate the effects of deer damage or save severely damaged trees. Wound dressings, pruning paints, latex paints, wrappings, and other alleged protective barriers do not help.
Type of Damage
The meadow vole is a small, brown, mouse-like animal. Though common in Iowa, the meadow vole is secretive and seldom seen by most individuals. Voles feed on grasses and other herbaceous plants. They also eat seeds, berries, tubers, and bulbs. In winter, meadow voles may eat the bark of small trees and shrubs. Vole damage typically occurs to the lawn and becomes apparent when the snow melts. Several narrow, meandering pathways appear on the lawn.
Mice and other small rodents can also damage perennials, trees, and shrubs by eating the crowns of perennials or chewing the bark from trees and shrubs. Plants with protective layers of straw or leaf mulch over winter are more prone to damage as mice overwinter in this material.
Damage to young trees and shrubs can be prevented by placing one-quarter-inch hardware cloth cylinders around plants. Bury the bottom 2 to 3 inches of the hardware cloth in the soil to prevent voles from burrowing under the cylinders. When mulching, keep wood mulches at least 6 inches from the trunks of small trees. Cover plant crowns and any portions of stems or trunks surrounded by straw or leaves with hardware cloth before placing the winter mulch layer. Poisons and baits can be put into the straw or leaves when other control methods have failed. The use of poisons can be a risk to pets and children, so use them with caution.
In lawns, vole populations can be kept to a minimum with regular mowing. Mow Kentucky bluegrass lawns at a height of 2½ to 3½ inches. Continue to mow the lawn until the grass stops growing in the fall (typically early November in Iowa). Cut or destroy tall weeds adjacent to lawns and gardens to reduce food resources and cover.
How to Manage Mice and Vole Damage If It Occurs
Meadow voles usually don’t cause serious harm to lawns. Damaged areas usually recover on their own within a few weeks. Reseeding may be necessary when damage is severe.
Damage to woody plants can be managed in the same way damage caused by rabbits is managed.