What is snow?
Snow! Some of us love it, some of us despise it, and some of us shrug it off as a fact of life in Iowa. Skiers and snowshoers head outside to exercise, and children of all ages plop to the ground to put their marks on untouched expanses of fresh, clean, white. Is there anything more beautiful than the sparkle of fresh snow on a clear winter night?
What, exactly, is snow? It’s white stuff, right? Actually, snow is translucent. Snow appears white to us because it reflects as much as 90% of the light that hits it, with no color being absorbed more than any other. Deep snow, however, absorbs more red light, so deep snow and deep pockets of snow may appear blue. Someday after a good snow, look at the shades of blue in the drifts and ruts along the side of the road.
Most of us snipped paper snowflakes when we were little, and we learned that every snowflake has six sides. The six sides are the result of the crystal that forms when a cold drop of water freezes onto a particle of dust or pollen. As the crystal falls through the atmosphere, extensions form on it, with additions to these extensions – always symmetrical on each of the six sides – taking unique shapes as the crystal moves through changes in humidity and temperature. Each snowflake encounters these conditions at different times in its development, resulting in almost infinite variations. Although we have been told that no two snowflakes are alike, scientists (those with lots of time on their hands?) have demonstrated that identical snowflakes can indeed occur.
Snowflakes vary in size as well as shape. Although the largest individual snow crystal was measured at 0.4 inches, crystals sometimes stick together to form much larger snowflakes. We have all witnessed snow falling in large clumps. Occasionally, people have measured such snowflakes clusters as large as dinner plates.
As to the moisture content of snow, we often hear that ten inches of snow holds one inch of water. In reality, the amount of water in snow varies depending on factors such as wind, temperature, and the crystal structure of the snow. Ten inches of snow can contain as little as 0.1 inches of water, but most snow is 4 to 10% water.
When I was in elementary school, a worksheet asked what sound was made when we walked on snow. I answered “crunch,” and my response was marked wrong! I was supposed to know that footsteps on snow were silent. Actually, both answers are correct. At colder temperatures, the friction of snow particles against each other when they are compacted causes a creak or a crunch – the colder the temperature, the louder the sound. On the other hand, at warmer temperatures, snow particles glide past each other without the friction and, therefore, silently.
Snow also affects sound itself. Because fresh snow absorbs sound waves into its surface, sounds can seem dampened and muffled. After periods of thawing and refreezing, snow develops a hard surface that reflects sound waves. In these conditions, sound may travel further and seem clearer.
Every state in the United States has experienced snow, even if just a dusting. In Hawaii, snow occurs on mountain tops. Key West has never had snow, but the average yearly snowfall in Valdez, Alaska, based on NOAA records gathered from 1981-2010, is an incredible 326.3 inches per year! Of large cities in the U.S, the greatest average yearly snowfalls occur in Rochester and Buffalo, New York, and Cleveland, Ohio. These are cities that receive the so-called “lake effect” snow coming off Lake Erie and Lake Ontario. For the record, the average snowfall in Waterloo, according to these same records, is 34.5 inches.
Not surprisingly, snow has become a factor in horticulture terminology. The Latin root for snow is niv-, and it can be found in names such as those for snow pear ((Pyrus nivalis) and snowdrop (Galanthus nivalis). The Greek root for snow is chion-, and we see that, for example, in Chionanthus virginicus, the botanical name for the white fringetree, which has snow-flurry-like white blossoms. “Snow” appears in common names for plants displaying white color or that withstand snowy climates, such as snowberry and the hydrangea “Snow Queen.” Or how about Rhododendron ‘Boule de Neige,’ (“snowball” in French)?
How Snow Affects Our Gardens
Like our opinions of snow, snow can have both good and bad effects on our gardens. Branches of evergreens such as arborvitae get weighted down and can break from the weight of heavy, wet snow. Or freeze-thaw cycles involving snow cover can result in breakage when branches are caught and pulled down in the crusty, settling snow layers. Prevention involves shaking the snow off branches or carefully brushing off the snow with a broom. Multi-stemmed plants such as arborvitae can be wrapped in twine in the fall.
Deep snow keeps some wildlife – rabbits and deer, especially in our area – from gathering food from the ground, so they munch on higher branches within their reach. Deep snow also allows smaller garden critters such as voles to gnaw on our buried plants and eat the bark at the base of trees as they take advantage of the spaces between the soil and the bottom of the snow layer. To avoid these kinds of damage, gardeners need to be both proactive and vigilant. We can protect our smaller trees and bushes – the tender tops as well as the bases – by enclosing them in cages or fencing in the fall and adding barriers as soon as we see where more foraging is taking place.
On the up side, snow can be a life-saver for our garden plantings. Dry, fluffy snow is an excellent insulator. Even an eight-inch layer of fresh snow can keep the temperature at soil level at a safer 32 degrees, protecting the tender roots of less hardy plants. It also guards plants – especially perennials such as mums and daisies – against freeze-thaw cycles that cause heaving of their roots. Once roots have been exposed, they have no protection from subsequent freezing temperatures. Besides the cold, sun and wind can dry plants out, and a layer of snow can help with this as well. Shrubs and perennials under the eaves of a house where snow does not naturally accumulate can benefit from a dressing of snow from elsewhere. Finally, melting snow provides much-needed moisture for spring growth. Caution needs to be taken, however, that snow does not accumulate in areas of poor drainage. Water-logged areas resulting from snow melt in spring are as damaging to plants as any amount of snow and cold.
The topic here has been snow. Cold winter weather, with or without snow, has its own beneficial and detrimental effects on our gardens. Cold temperatures can help control insect pests, killing some over-wintering grubs and larvae. Various plants – spring bulbs, for example – need a period of cold to produce flowers. Plants such as forsythias, on the other hand, may not blossom after a particularly harsh winter. Young trees, especially those with thin bark such as maples, are susceptible to sun scald and will benefit from being wrapped during the winter. (This wrap needs to be removed in spring.) And we all know how a late frost can kill tender new shoots and buds, robbing us of plant growth, blossoms, and fruit.
Choosing winter-hardy plants is the first step in preventing weather-related losses. Placement of plant materials can also affect a plant’s ability to survive and thrive. North and east exposures stay cooler in spring, so trees such as magnolias and fruit trees will tend to blossom later and not be damaged by the widely fluctuating spring temperatures. Another way to protect plants from injury by late frosts is to mulch them, keeping soil from warming too early. Shallow-rooted plants such as strawberries are particularly susceptible to damage from heaving. Where snow cover is not available, a layer of mulch will help mitigate this problem, although the mulch needs to be pulled away from the crowns of plants in spring to prevent rotting.
Will you think of snow a little differently now? At the very least, take a look outside and make sure your garden is safe from winter’s hazards. Meanwhile, sit back with a stack of seed catalogs and dream of spring!
Written by Rita Lynn
“Ten Facts About Snow That Might Surprise You,” by Jonathan Belles, https://weather.com/science/weather-explainers/news/ten-facts-about-snow
“Snow Science,” https://nsidc.org/cryosphere/snow/science/characteristics.html
“Snow and Plants,” https://nsidc.org/cryosphere/snow/plants.html
“How Do Snowflakes Form? Get the Science Behind Snow,” http://www.noaa.gov/stories/how-do-snowflakes-form-science-behind-snow
“Snow or Lack Thereof – Effects on Landscape Plants,” http://extension.oregonstate.edu/gardening/snow-or-lack-thereof-effects-landscape-plants
“How Plants Are Affected by Cold and Winter and How to Protect Them,” by Sandra Mason, Extension Educator, Horticulture, http://web.extension.illinois.edu/cfiv/homeowners/980110.html
“Caring for Plants, Shrubs and Trees In Snow,” by Richard Jauron and Greg Wallace, http://www.extension.iastate.edu/article/yard-and-garden-caring-plants-shrubs-and-trees-snow
“Let It Snow,” by Nancy Rose, Editor of Arnoldia, http://www.arboretum.harvard.edu/let-it-snow/
“Valdez Snowfall Totals and Accumulation Averages,” “Snowiest Cities in the United States,” and “Average Snowfall in Iowa,” www.currentresults.com