Snow, Wonderful Snow!

We finally have good snow cover! I only wish it had been earlier. This winter will be a trial for northern gardeners. If you live in USDA hardiness zones four and lower, the amount and timing of the snowfalls are greater nail-biters than a Tom Clancy novel. Why? If you are new to gardening in cold climates, you may not know how important good snow cover is. It can mean the difference between survival and death of new plantings and marginally hardy plants. The timing can also have a profound effect on coddled lawn grasses.

Most folks look at the snow as just a wintertime nuisance that has to be tolerated. Gardeners quickly come to know that it is the insulation that makes growing many things in this harsh climate possible. If we don't get it, we must mulch very heavily with something like chopped leaves or straw to replace the protection it provides. Some plants, like the beautiful, tall Delphiniums that southern gardeners envy so, often succumb to crown rot if their mulch mats down and holds moisture. A good snow cover provides the right combination of coverage and support until it melts away in the spring, leaving the soil damp, but open. Many plants are more reliably hardy in Bemidji (zone 3a), where you can count on the snow cover, than in the Twin Cities (zone 4a).

Plants that are listed as hardy for our zones (to -30ºF or lower) arrive at that degree of hardiness only after they have achieved their peak winter dormancy. This happens gradually with the shortening days and lowering temperatures of fall. If we get sudden temperature drops before the snow insulation arrives, they can be damaged, even killed. Insulation provided by the snow tempers those severe drops and lets plants complete the process.

New plantings are always in jeopardy from frost heave, the alternate thawing and refreezing that can tear apart fragile, developing root systems. A good snow cover can keep the ground temperature on a more even upswing until it melts. By then, most of the danger is past.

Is snow cover ever bad for plants? It can be. Lawn grasses suffer the most. When snow comes early while the ground is still warm, the snow at the bottom of the layer will melt and make an inviting home for fungus diseases. In spring, when the overlying snow finally melts, great patches of a disease referred to as "snow mold" may be revealed. If it is extensive and severe enough, the whole lawn may have to be replanted. At best it will have to be patched with the resulting spotty effect.

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