A good snow cover acts to insulate soil and can actually help plants. (Stock Xchange)
Every morning I look out my office window into a snow-covered garden and wonder what’s going on under that thick, white blanket. The record snowfalls and frigid temperatures have even the glass-half-full guys and gals talking to themselves.
For those of us gardeners who like to push the envelope when it comes to zone hardiness, the deep and continuous snow cover is actually a blessing, especially when temperatures fall to single digits and below. The fluffy stuff slows the heat loss from the earth and insulates the ground from the dreaded freeze-and-thaw conditions that tear up plants’ roots. Water that comes out of my well more than 100 feet underground is 53 degrees, summer and winter.
The USDA cold hardiness zones define a minimum range of temperatures that plants and trees can survive in, but as we gardeners know, there are many variables, including soil types and porosity, moisture content and protective coverings ranging from snow, to sod and other vegetation, to mulch. All these elements contribute to microclimates — areas where the soils hold or lose more or less heat throughout the year.
Exposure to wind and sun is also a factor. The freeze depth will be deeper in shaded areas, so that would include northern and western sides of buildings. Bitter cold winds also can have a chilling effect on exposed areas, such as berms.
Heat transfer also affects soil temperatures. The warmth seeping out of the walls of a basement or cement slab, known as heat transfer, will also warm the soil surrounding a heated building and reduce the depth of freeze. However, the area surrounding an unheated building may develop a deeper frost depth.
How effective is snow cover as a thermal buffer and how much of a difference can all these variables make? In the Reford Gardens in Quebec, more than 100 miles north of the northern tip of Maine, the iconic zone 7 to 8 Himalayan blue poppy (Meconopsis betonicifolia) flourishes, thanks to the garden’s near sea-level location and deep, winter-long snow cover.
Another benefit of a cold winter is the reduction of insect pests. Armyworms, corn earworms and potato leafhoppers cannot survive the freezing temperatures of Michigan winters — they migrate from warmer states. But the arctic vortex has reached into the South several times this winter, bringing with it sub-freezing temperatures, which should knock back these tender pests. Hopefully we will also see a reduction in fungal diseases.
Nancy Szerlag is a master gardener and a Metro Detroit freelance writer. Her column appears Friday’s in Homestyle. To ask her a question go to Yardener.com and click on Ask Nancy. You can also read her previous columns at detroitnews.com/homestyle.