Here in Kentucky, when snow is forecast, the obligatory trek to the grocery store to stock up on bread and milk begins. Even though the frozen stuff rarely lasts more than a couple of days, people strip the shelves bare just in case we're snowed in for weeks. We're not quite in the Deep South (where the milk and bread panic reaches a truly insane level) but snowfall is so infrequent that it is still a novelty. Most people do not realize that snow is a good thing and our gardens are better when it falls.
Snow is a natural insulator. It traps quite a bit of air and just like the goose down in your coat, it holds in heat. Some tests report that snowfall raises the soil temperature as much as 2 degrees F for every inch that is on the ground. It insulates the roots of your perennials and prevents heaving that comes from the ground freezing and thawing. It also provides necessary moisture for plants, especially evergreens, which require more winter moisture than dormant deciduous trees and shrubs.
Wheat farmers need snow to cover their just emerged winter wheat seedlings and insulate them from harsh winds as well. They've learned to leave stubble from the previous season in place to catch blowing snow and hold it on the fields. This is something we as gardeners can learn from when working our perennial beds. A little stubble and scruff serves to capture snowfall and hold it over the roots of our peonies, hostas and daylilies, acting as cozy blanket. Snow cover in your perennial beds also protect egg cases and chrysalis of beneficial insects and moths and it is simply an 'old wives tale' that snowcover kills insects. All insects, good or bad are insulated against the weather for whatever area where they live.
Snowfall means free fertilizer. Falling snow captures nitrogen from the air and deposits it on the ground and on evergreen leaves where it is absorbed by the plants, even dormant plants can absorb nitrogen from snow. Here in west Kentucky, it has long been said that the best time to seed your lawn with new grass is when you can scatter it over snow. This nitrogen (and trace amounts of ammonia) isn't present in a significant measure, however every little bit helps.
Warm winter days can trigger plants to break dormancy too early and when temperatures return to normal, they suffer as a result. A blanket of snow keeps these plants sleepy and snug until spring actually arrives. They wake at their appointed time and paint your garden with riots of color. Many people think that pruning trees and shrubs in late fall or early winter makes for a neater garden, however, here in the Mid-South we have so many warm days scattered in with the colder ones that often freshly pruned shrubs will break dormancy too early. It is much better to wait until late winter to prune things like crape myrtles and roses to prevent the early awakening. Here in west Kentucky, I usually prune mine sometime in February.
One of the few down-sides of snow cover is that it provides a safe predator-free passageway for voles and other garden vermin. I've even taken to pulling the snow from the trunks of some of my favorite trees and shrubs, such as my Japanese maple and azaleas if it lingers more than a day or two. However, in my area, snow rarely lingers and the varmints aren't able to get comfortable.
You should also knock extremely heavy snowfall from the branches of shrubs and small trees to prevent branch breakage if you can. Snow isn't as much as a problem here as ice is. Ice storms can cause damage to even mature trees and there isn't much you can do about it except to prune the broken branches back come spring. We had a massive ice storm hit our area in January of 2009 and we're still recovering from the effects of it. Our mature hardwood forests will never look the same. If an ice storm happens at your home, it is important to prune the broken and damaged branches back to clean wood to prevent disease and rot, not to mention the unattractive silhouettes. This is an exception to the rule and these storms are rare indeed. The beauty of the winter landscape should inspire. I feel fortunate to live in an area with four distinct seasons and each one has its charms.
"Winter is coming." shouldn't strike fear in a gardener's heart. Unlike the residents of Westeros, it isn't going to bring snarks or grumpkins out of their lairs. We should enjoy the beauty of the snowfall and snuggle up with a hot cup of coffee or hot chocolate and dream of spring while it works for us protecting and nourishing our gardens.