The wintery beauty of snow-covered trees has provided inspiration for artists, photographers, writers and poets for generations. In addition to its aesthetic appeal, a blanket of snow can insulate trees from potentially damaging fluctuations in ground temperature. Unfortunately, snow also has the potential to do serious damage to trees and shrubs.
On the plus side, snow modulates root temperatures and provides moisture for spring. Since snow is a poor heat conductor, the temperature changes very slowly from the top layer of the snow to the bottom. This keeps the ground from heating and cooling as air temperatures fluctuate, a process that can cause the ground to heave and damage roots. With 8 inches of snow on the ground, soil temperature will seldom fall below 23 degrees.
On the negative side, snow can cause four kinds of damage to trees and woody shrubs: bending, breaking, splitting and falling or uprooting. Whether woody plants will be damaged in one of these ways depends upon several factors. Evergreens with needles, for instance, can bear more snow weight than broadleaf evergreens. A tree's form can also be a factor in how well it will withstand heavy snow. Pine, spruce and fir with wide spreading branches are more likely to be damaged by heavy snowfall than trees with steeper angled branches.
Arborvitae is a good example of a plant that doesn't handle heavy snow well. They tend to get tall, with multi-stemmed branches that are low to the ground. Although arborvitaes are common foundation plantings, they are easily crushed by snow falling from roofs.
The type of snow is an important factor in potential damage to trees and shrubs. Wet snow is more damaging than powdery snow because it is heavier and clings to branches. Ice is especially damaging, making branches more brittle and likely to break.
The timing of a snowfall can also be a factor. With a wet snow in March, when there are no leaves on the branches, a deciduous tree may be able to withstand damage well. But the same snowfall in late spring or early fall, when the tree is leafy, could add unbearable weight. The Halloween snowfall in 2011 was especially damaging for this reason.
So, how do you prevent snow from damaging your trees and shrubs? The easiest way is to put the right plant in the right location: avoid planting sensitive shrubs in locations where snow will avalanche from the roof or where they will encounter heavy winds. If a treasured shrub is in a vulnerable location, it can be protected in several ways. Many people protect vulnerable shrubs with wooden A-frames. Shrubs can also be wrapped in burlap; tying up shrubs like boxwood or rose bushes will help to prevent branches from being snapped off by snow weight.
When heavy, wet snow arrives, the burden on your shrubs can be eased by using a broom and gently—GENTLY—brushing off some of the snow weight. Without the extra weight, most shrubs and young trees will gradually straighten up. If you’ve missed the opportunity and heavy snow or ice has encrusted branches, it may be better to simply wait until temperatures increase, as you can sometimes further damage branches by forcibly removing snow.
We have more information on winter tree care on our Web site.