#1 Threat: Most damage to trees and shrubs during winter is from animals. Voles burrow under the snow and feed off the bark of landscape plants all winter long. Rabbits “prune” the same plants above the snow line. Deer eat or rub everything above the rabbit feed-line. It’s a wonder anything but voles, rabbits and deer survive.
The best, almost-guaranteed step to eliminate this threat is to exclude the critters from the plants. Arrange ¼ inch hardware cloth around the stem(s), starting from the ground-line and up to the first branches. Or you can create a protective fence around the whole plant with hardware cloth, which is available at any hardware store.
A taller (5 feet or more) fence around your prized evergreens or shrubs will discourage the deer from grazing. To prevent deer rubbing damage to tree trunks, put 3-4 steel fence posts around the tree trunk, far enough from the stem to avoid damaging the roots but close enough that the antlers can’t reach the bark.
#2 Threat: Deicing chemicals kill plants and are very toxic to tree and shrub roots, foliage, flower, and leaf buds. If you are near a heavily-used road with speed limits nearing 45 mph or greater, keep sensitive plants at least 60 feet away, or build a protective fence between the road and the plants. If you can’t build a fence, wrap the plants in burlap for the winter.
The best way to avoid damage from deicing chemicals is to avoid using them! Shovel early and often whenever possible. When you do use chemicals, carefully follow package directions.
#3 Threat: Water-stressed plants can suffer from more dieback, stem cracking, and death than those that enter winter well-watered. Water throughout the summer and autumn, right up to the point when the frozen ground can no longer absorb water. Mulch around your trees and shrubs as far out as you can stand it with 3-4 inches of organic mulch. This reduces the amount of water lost to evaporation, keeps the soil warmer in the autumn and often and keeps the soil from freezing beyond a thin crust at the top.
#4 Threat: If your trees and shrubs chronically break apart from heavy winter snows and ice loads, tie the stems together for support before winter starts. If possible, tie the branches and stems on shrubs and multiple-stemmed trees (like arborvitae) with pieces of burlap or old bicycle inner tubes or “tree-chains” at a point about 2/3 the distance between the ground and the top of the plant. This artificial support will keep the plants from flopping open and breaking branches and stems.
None of these steps are very effective after damage has already occurred so the best time to take care of the plants is around Halloween and then remove any artificial supports that can affect healthy growth by Easter.
For more information, read the University of Minnesota Extension online publication, Protecting Trees and Shrubs Against Winter Damage, by Swanson and Rideout.