Blanket of snow is a poor man's fertilizer

Jeff Lowenfels

Termination dust, a quaint Alaska phrase that used to be applied to that first snow and therefore the end of the construction season, now really only applies to gardeners by signaling the end of the outdoor growing season. For the next nine months snow acts like a concrete barrier to our favorite pastime until warm weather crashes into it.

Ah, but ever the optimist, as anyone who gardens in the Great State has to be, I look for the good in snow.

For one, snow provides insulation that prevents soil temperatures from constantly fluctuating between freezing and thawing. The reason this matters is because these changes cause the water in the soil, and thus the entire mass, to expand and contract. Roots can be damaged, even tossed out of the soil. The same goes for all those fall-planted bulbs.

In addition to preventing frost heave by keeping temperatures below freezing, the snow prevents plants from starting at the wrong time. By the same token, most plants won't start up in the spring unless they have had exposure to a certain number of days of cold. Snow cover during a prolonged warm spell is a yardener's dream.

In this regard, it actually can pay great dividends if you pile snow on your garden beds. This is especially so if you are one of those stubborn readers who refuses to apply an insulating cover of mulch over perennials and around trees and shrubs. Remember, we have had winters where we have not had a good snow cover and the frost went down so deep we have had to worry about our pipes, not to mention our plants.

There is something else that happens when it snows: nitrogen is deposited by the snow and absorbed either into the soil food web residing and active at low temperatures or by plants as a result of nitrogen fixation, a microbial activity which, astonishingly enough, can take place even at low temperatures. Even when the soil is frozen, its eventual thaw can result in the absorption of nitrogen.

I had always been just a bit skeptical of the fact that snow contains nitrogen. My research when I was first asked this question back in the late '70s -- which I don't need to remind you was pre-Internet and Google -- failed to turn up any reliable data confirming what I considered to be just another gardening wives' tale.

Well, it turns out not only snow, but rain as well, contains nitrogen compounds that were suspended in air as they formed. It is estimated that 2 to 12 pounds of nitrogen are deposited per acre as a result of snow and rain. Most of this nitrogen comes from emissions as a result of burning fossil fuels and industrial manufacturing. The rest comes from lightning fixing atmospheric nitrogen, which makes up 70 percent of air, as I recall.

In fact, it seems the amount of nitrogen in snow and rain has increased dramatically since industrialization and the advent of the automobile. One study I read indicated that by the 1980s the amount of nitrogen deposited in the Colorado Front Range was 30 times greater than it was before the Industrial Revolution. Another study says that this number has since doubled.

Granted, to a chemical gardener, 2 to 12 pounds per acre is not that much nitrogen when one considers the suggested rate of application is 3 to 5 pounds per 1,000 square feet. (An acre has 43,560 square feet). But in more and more areas, particularly along rivers and in watersheds, the nitrogen from rain and snow, particularly when snow melts in the spring, has been enough to cause serious changes in the ecosystem.

Add to this studies that show an increase in nitrogen mineralization -- uptake by microbes a la soil food web -- in tundra areas when there is snow cover and it becomes clear that snow falling in your yard can be counted for something, especially if you have not damaged your soil's microbes with harsh chemical fertilizers. No wonder the old wives' tales called snow "the poor farmer's fertilizer."

So curse it if you must, but know that there is some good from any snow that falls.

Jeff Lowenfels is a member of the Garden Writers Hall of Fame. You can reach him at www.gardenerjeff.com or by joining the "Garden Party" radio show from 10 a.m. to noon Saturdays on KBYR 700 AM.

Garden calendar

OUTDOORS: Stake driveways and pathways so you know where to put snow.

INDOORS: Come on, get those lights up for indoor growing.

AEROGARDENS AND OTHER HYDROPONICS SYSTEMS: Now is the time to have them going and growing.


JEFF LOWENFELS
GARDENING