Snow & Ice

14 December 2005

Virginia Cooperative Extension, Charlottesville/Albemarle County Office
460 Stagecoach Road, Charlottesville, Virginia 22902
phone: 434.872.4580   fax: 434.872.4578

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Looking out your window today you might see some snow and you might be wondering about how to protect your plants from the forces of nature. Before addressing any protective or remedial action that a gardener might take, I think it only fair to come to the defense of snow for its positive contributions. Not only does it provide us with a beautiful backdrop to birds feeding on the deck, but when deep enough, it gives us a reason to stay home for the day. Snow also offers warmth and wind protection to overwintering spinach, pansies, and multitude of perennials that we had not yet mulched.

Exposed areas with fluctuating temperatures are tough places for plants and often we see a lot of winter kill with this type of weather. Snow is an excellent insulator with thousands of tiny air pockets that hold the soil warmth around the plants it covers. A thick layer protects plants from the winds that dry and tear at leaves and buds. Snow is good for preventing erosion and stabilizing soil temperatures as well. Early and lasting snow that comes before a deep freeze will insulate the ground and keep the frost from penetrating deeper, reducing some of the freezing and thawing that forces perennials out of the ground.

The amount of snow is important as well as when we get it. Early season snows before temperatures get too cold will help roots survive. Snow can gradually replenish the subsoil moisture levels when it melts slow enough to seep in rather than run off as the winter rains too often do. But as with everything, there is a negative side to snow. It melts and makes a mess, it creates chaos when those other drivers from wherever do not perform up to par on snow-covered roads, and when it comes down long and hard enough, it breaks tree branches and splits shrubs. Once the snow or ice begins, there is relatively little that you can do. What you can do is prevent the damage from occurring by selecting plants that are least susceptible to snow or ice damage and locating plants where they are least likely to be hurt.

Shrubs, such as boxwood, yews, and arborvitae, have even greater problems if planted under the eaves of a house where snow can slide off the roof. If they are already planted there you can erect snow deflectors over shrubs under the drip line of houses and other buildings to protect them against avalanches falling off the roof. Along a sidewalk, Japanese hollies and azaleas are severely damaged by the added burden of snow and ice shoveled from the walk and dumped on them. De-icing salts then weaken the broken plant further. Knocking snow off (tap the branches gently) as it accumulates can help avoid breakage, but this requires repeated efforts throughout the storm. Few gardeners will take the 2 am shift. Ice cannot be easily removed and you often do more damage trying to remove ice. It is best to let the sun melt the ice. After the snow and ice have melted and the damage is repaired, it is time to plan for a landscape that is less likely to be damaged by forces you cannot control.

In addition, if snow cover is not very deep, the sun can penetrate it, warming the soil beneath and speed thawing from the bottom. Also, when snow gets dirty, the dirt absorbs heat from the sun and the snow melts from the top. This is why snow turns to slush so quickly in large cities. It is also why new snow melts so quickly when it falls on a layer of dirty snow.

A number of flood studies show that between 50 to 90 percent of a heavy snowfall may be intercepted by tree tops in a dense, coniferous forest - little reaches the ground. In deciduous forests most of the snow accumulates on the ground with little held by the trees. Therefore, the ground freezes hardest in a coniferous forest. Since it is difficult for the sun to warm the ground in such a dense forest, the ground tends to remain frozen quite late in spring. In a deciduous forest, the soil is covered with snow, keeping soil temperatures higher. Usually there is also a large accumulation of organic matter around the trees. Organic matter can absorb large quantities of moisture as snow melts, therefore runoff is decreased.

To a certain degree we can control the soil temperature on our own properties through the type, number and placement of trees. Properly placed windbreaks can shield the garden from blasts of wind as well as prevent snow from blowing off in areas where it is needed. In addition, piling organic mulch over the garden in winter acts in the same way as the forest organic debris described above. A deep layer of mulch (shredded leaves, pine needles, straw or hay) insulates the soil and holds snow very well.

Ice Storm Susceptibility of Tree Species Commonly Planted in Urban Areas

Susceptible

• American elm
• American linden
• Black cherry
• Black locust
• Bradford pear
• Common hackberry
• Green ash
• Honey locust
• Pin oak
• Siberian elm
• Silver maple

Intermediate Resistance

• Bur oak
• Eastern white pine
• Northern red oak
• Red maple
• Sugar maple
• Sycamore
• Tuliptree
• White ash

Resistant

• American sweetgum
• Arborvitae
• Black walnut
• Blue beech
• Catalpa
• Eastern hemlock
• Ginkgo
• Ironwood
• Kentucky coffee tree
• Littleleaf linden
• Norway maple
• Silver linden
• Swamp white oak
• White oak

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For more information about landscape topics contact your local Virginia Cooperative Extension office. The local Virginia Cooperative Extension office numbers are Albemarle 872-4580, Fluvanna 591-1950, Greene 985-5236, Louisa 540-967-3422, and Nelson 263-4035.

Virginia Cooperative Extension will be offering Master Gardener classes in Albemarle, Nelson, Fluvanna, and Louisa counties in early 2006. Please call your local Extension office for more information.