We associate snow with cold, but there’s a reason Eskimos use it to build houses – snow’s a good insulator. Mother Nature insulates the ground from too-deep freezing by blanketing it with snow.
The root system of plants can’t take cold temperatures the way the above-ground branches can. While the branches of adapted trees and shrubs can easily withstand -30 degrees F., if the roots were exposed to those temperatures, the plants would likely die. Soil naturally moderates the temperature, but it’s often not enough. That’s why snow cover is so important. Snow insulates the soil so the cold air temperature can’t penetrate into the ground as deeply.
Besides moderating the soil temperature, there’s another important benefit of snow cover. Snow keeps the soil uniformly frozen. Bare soil can be warmed and thawed by daytime winter sunshine. Soil refreezes quickly at sunset. These cycles of freezing and thawing of bare soil cause roots to break and tear. Plant like perennial flowers and strawberries can even be heaved out of the ground, with roots partially exposed.
Mid-winter thaws feel great to us humans, but thawing temperatures can cause bare ground around perennial flowers. The insulating effects of snow can quickly be lost. Then when cold returns, the plants are exposed. Even tough, winter-hardy perennials can be damaged with “open” winters in which we have little snowfall, or we lose the snow we’ve had. This happened several years ago, resulting in death of even reliable perennials like peonies, hosta and iris.
What to do? When shoveling snow – toss extra on perennials. This might mean doing some extra shoveling, if the plants aren’t close to sidewalks. In backyard perennial gardens it’s sometimes necessary to shovel some snow from the lawn onto the perennials. If snow begins to disappear from perennials, there’s usually a deeper drift of snow somewhere from which to borrow.
Preserving snow cover is a main reason why it’s recommended the tops of perennials be left intact during winter, because they help catch and preserve snow.
So although a snowy winter might not be what us humans would prefer, it does wonders for perennial flower survival. Happy gardening!