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Think Snow – Gardens and Forests Need It

Think Snow – Gardens and Forests Need It

By Paul J. Hetzler

In her poem “It Sifts from Leaden Sieves,” Emily Dickinson lauds the sublime beauty of snow – gossamer flakes that garnish a forest, wispy grains that infiltrate nooks and crannies, and wind-sculpted rings of snow around fence posts. Given that the poet lived in a time before cars and stayed in her bedroom for 20 years, she never had to shovel snow, trudge through it, or drive in it. One is less apt to admire “alabaster wool” when the plow wings a mountain of it onto the driveway you just shoveled.

Snow does a lot more than make skiers happy and pedestrians and commuters miserable, of course. In northern latitudes, ecosystems have evolved with winter snow cover, and need it to stay healthy. This is in large part because snow carries with it trace elements crucial to plant life. More importantly, snow contains plant-available forms of nitrogen, a nutrient often in short supply. When snow releases a whole winter’s worth of nutrients in the spring, it can make a difference to trees and crops. This is why snow has been called “the poor person’s fertilizer.”

Since air is 78 percent nitrogen (N), you’d think plants would have all they need. But atmospheric nitrogen, N2, is a stable, inert molecule that plants are unable to absorb. Lightning can zap nitrogen gas and change it to a plant-friendly form, but this accounts for very little of a plant’s nutrient budget.

The majority of nitrogen used by plants is made by soil bacteria that break apart the N-N bond of gaseous nitrogen, converting it to water-soluble forms that plants can slurp up. Ironically, the process of breaking N2 is called nitrogen fixing. It’s where the saying, “if it needs breaking, fix it” comes from. OK, maybe that’s not a real saying.

Snow is a better fertilizer today than it was years ago. There’s a great outfit called the National Atmospheric Deposition Program (NADP), which measures stuff that falls out of the sky that isn’t some form of water. According to the NADP, the vast majority of today’s snow-borne nitrogen is from pollution.

Coal-burning power plants and motor vehicles spew out various nitrous oxides, which are not great for us to breathe, but when they get washed into the soil, they act as nitrate fertilizers. Ammonia, another type of plant-available nitrogen, escapes from manure piles and lagoons, as well as from commercial urea-based fertilizers.

So how much fertilizer is in the snowdrifts blanketing the Northeast and Great Lakes regions these days? Because we’re the “beneficiaries” of pollution that drifts from industrialized areas west of us, we get more nitrogen in our snow than the rest of the country. If historical averages can be trusted (let’s pretend they can), we get somewhere around 5.5 kilograms of N per acre. Depending on the crop, a farmer may apply on the order of 70 kg of nitrogen per acre, so 5.5 kg is small potatoes. But it’s not chopped liver, either, which is high in nitrogen but not an ideal soil amendment.

Snow-based nitrogen can be a significant boon to ecosystems on marginal soils. In a year with abundant snowfall, maple-sugar bushes, timber lands and pastures benefit from “poor person’s fertilizer.” Snow brings a fair bit of sulfur, an essential plant nutrient. It can make soils more acidic, too, so let’s call it a mixed blessing.

We depend on the moisture from snow as well. In most years, the snow melts gradually, with nearly all the moisture going into the soil. This gentle percolation is in contrast to summer rains, a percentage of which – sometimes a large portion – runs off and doesn’t benefit the soil.

When topsoil is saturated, or as agronomists say, “at field capacity,” excess water seeps down through the soil profile. Eventually it becomes groundwater, raising the water table and recharging our aquifers. Most water wells in the Northeast tap into unconfined aquifers. Water that goes into the ground in a given location is the water that comes out of the well there. Such aquifers depend on snowmelt, as well as prolonged heavy rains of spring and fall, for recharge.

Unfortunately, this historical pattern may not last. In spite of record cold out West in January 2024, winters are getting warmer and shorter, thanks to climate change. Winter is actually heating up faster than any other season. Without a significant snow pack, the groundwater recharge we always get in the spring will diminish. And when some of winter’s precipitation falls as rain, nutrients will run off while plants are dormant, and thus be lost to those ecosystems.  

Those who work in field and forest should take heart at the mounting snowbanks, not despair of them. Now if you’ll excuse me, I’m headed to the garden with the rototiller to till the snow. I’m pretty sure I have some seed packets of Iceberg Lettuce, Snow Peas, and Mixed Frozen Vegetables around here somewhere.

By Paul J. Hetzler
Canton, NY

Paul Hetzler is the Horticulture and Natural Resources Educator for Cornell Cooperative Extension of St. Lawrence County.