Snow has been called the poor man's fertilizer. That's an old wives' tale. If it were a new wives' tale, snow would be called the poor person's fertilizer. In either case, if it is true I have gotten rich this winter, at least in fertilizer, which some say I have always had in ample supply, though they use a different word.
The snow load has fallen gently on me. Every year I wait for the first significant snow fall and scan the newspapers for an article that usually begins, “Elderly man suffers heart attack shoveling snow.” I cut it out and pin it up on the refrigerator door where my wife can't miss it. I have been doing this for so long that I started out looking for articles that began, “Middle aged man ...”
So, is it true? Sorta. The air is 78 percent nitrogen, and as snow falls through it, it picks up some along with tiny quantities of trace elements like sulfur. So snow does add nitrogen, the king fertilizer element, to the soil. So does rain, probably more efficiently, but rain runs off. Snow piles up, I'm told, and it can sit there and wait before unloading several snowfalls slowly in spring, when plants are really hungry for it.
Actually it turns out that snow has more nutrients now than it did when old wives were young. Cars and power plants are putting more nitrogen oxides into the air and more fertilizer into the ground. Every dark cloud, even pollution, has a silver lining.
A melting snow cover and summer rain can add up to 12 pounds of nitrogen per acre. A farmer will commonly add 150 pounds per acre. So yes, snow is a fertilizer, but no, not enough to make a big difference. Even organic gardeners don't depend on it. As I said, the tale is sorta true.
That is only part of the story, though. More important than its fertilizing power is its insulating ability. A blanket of snow through the winter actually protects plants. The coldest nights don't penetrate into the soil, nor do the warmer days.
Many gardeners think a winter mulch is intended to keep the plant warm, but its real purpose is to keep the soil cold.
What is commonly called winter kill is usually really spring kill, though we don't like associate those two words. Soil thaws during a spring warm spell, plants begin to grow, then an arctic front comes in and kills all the sprouts, making the plant wisely decide to wait until June. A good snow cover keeps the ground cold so plants just pull the blankets up tight and doze on until it all melts.
It also prevents the alternate freezing and thawing that can happen throughout the winter. This fiddles with the plant roots, especially those near the surface like mums, and breaks them. When it is time to grow again, there are fewer roots to provide the water and nutrients it needs for new growth. The plant dies, particularly if there is wind drying the new leaves. Snow cover solves all this.
It is particularly problematic with plants that were planted in fall. These really need to be mulched in open winters, which someone I know well didn't quite get to last fall. Snow makes me look like a better gardener.
While I don't shovel snow, I do go out after a major snow storm with a rake to shake the snow off the evergreens. My boxwood hedges and a row of columnar arborvitae have been grotesquely misshapen, and though they will probably need some straightening in spring, they shouldn't stay that way. Otherwise I love looking at snow through a window. And I will love watching it melt away.