Young trees and shrubs always are at risk through winter because their bark is still "tender." If enough snow falls to cover food supplies, however, rabbits and mice will chow down on almost any ornamental plant.
"This feeding can be severe enough that the tree or shrub ends up losing bark around its entire trunk. Any encircling cut or break in bark results in what's called girdling, and that's fatal to ornamental plants," said Ward Upham, horticulturist with Kansas State University Research and Extension.
He recommends protecting young ornamentals through their first winter or two.
"Since apple trees are a perennial favorite, I'd think about protecting them every year," Upham said. "I'd also keep an eye out from fall through spring for any sign that rabbits are feeding or mice are building tunnels nearby." Protection at this time of year both is and is not a simple issue, he said.
Shooting wildlife within city limits is illegal in Kansas. Rodent repellents generally require applications at temperatures well above freezing. Live-trapping can help reduce cottontail populations, but often has little to no effect on jackrabbits or mice. Typical mousetraps and over-the-counter mouse baits aren't really designed for outdoor use. Other types of killing traps come with lots of legal restrictions. No rabbit poisons are registered for use in the state.
"That's why when homeowners want to control rodents in early winter before damage occurs, they usually either call a pest control operator or try exclusion," Upham said.
For individual trees, the best exclusion is a trunk-surrounding cylinder, typically of one-fourth inch mesh hardware cloth or plastic drainpipe. The cylinder must extend 2 to 3 inches below ground (for tunneling mice) and 18 to 24 inches above the expected snow line (for rabbits on their hind feet).
"Even for apple trees, I'd advise removing this protection each spring--or at least checking it over. Sometimes tubes have been left in place and ended up girdling the trunk," the horticulturist warned. A chicken wire fence can protect shrub beds from rabbit feeding, he said.
"But that won't help if you've got a mouse problem. And you'll have to inspect the fenced area frequently. A hungry rabbit won't mind digging its way under a ground-level fence. In fact, it could end up trapped inside with the shrubs you're trying to protect," Upham said.