It’s okay to long for May temperatures during a deep January freeze. Many of us enjoy winter until just after the holiday season, at which point the snow and cold goes from being charming to being a nuisance (almost magically!) overnight.
As gardeners in Canada we frequently rate our winters using adjectives like “good/bad”, “hard/mild”, or “I was in the Bahamas for most of it.” But here’s an interesting question to ponder: what actually constitutes a “good” winter? We might prefer mild temperatures, but what about overwintering plants or insects?
It turns out, it really depends on who you ask. Let’s look at a few case studies.
Ask a Sugar Maple
Ask a sugar maple (or any other deciduous tree or large shrub, for that matter) what kind of winter it would like, and you’ll get a fairly consistent message: it doesn’t really matter, as long as the temperatures don’t significantly fluctuate.
Deciduous trees go completely dormant in the winter, as the tissues of their leaves can’t tolerate freezing temperatures. This is a great defense against the cold, but can spell trouble if we have a thawing period followed by a cold snap. Our trees are fooled into thinking spring is here, sending sap up to their most tender branches as they prepare to push out buds. When the thaw ends, freezing temperatures deliver a one-two punch — the buds and branches are injured as the sap freezes and expands, and a portion of the tree’s energy reserves are wasted.
Thankfully, most trees have enough energy stored to push out adventitious buds to replace those damaged by sudden cold or late frosts, but if our winter has a succession of freeze/thaw cycles, it can wreak havoc on many plants.
Ask an Evergreen
If you were to ask an evergreen what kind of winter it preferred, you’d get a wide range of answers. An eastern white pine, for instance, would be perfectly happy with brutal cold and harsh winds. Ask a boxwood the same question, and you’ll hear the near-opposite: they’d prefer nothing lower than -20oC, and the fewer windy days, the better.
One thing almost all evergreens will agree on — much to our chagrin — is that heavy snowpack is a good thing. Snow is very important for evergreens. It acts as an insulator, protecting their roots from the temperature extremes above. When snow melts during a midwinter thaw, it waters our plants for us (yes, evergreens need water in the winter; more on that here). Sufficiently moist soil takes longer to freeze and is usually much warmer than the air temperature. Snow also protects the base of our plants from most foraging rodents (though voles will still attempt to burrow under the snowpack).
If your evergreen is in a pot above ground, you’ll want to wish for mild temperatures. Cold snaps will cause severe damage to the roots of evergreens that are planted above ground.
The worst kind of winter for evergreens would be frigid and windy with absolutely no snowpack. A good winter for evergreens would be decently cold with heavy snowpack and a lot of overcast days. So far, the 2017/18 winter has been good for evergreens, at least in the London area.
Ask a Japanese Beetle
If you were to ask a Japanese Beetle what kind of winter it would prefer, it probably wouldn’t answer you, because it would be dead: adults live no more than 45 days, and our winters finish them all off. However, their offspring — white grubs — do survive the winter, and would be highly opinionated on the subject.
Grubs don’t like the cold; grub mortality spikes when soil temperatures dip below -10oC or when it stays consistently below freezing for a few months straight.
Like our plants, grubs also reap the benefits of heavy snow, since it acts as an insulator.
It’s unfortunate, but the best kind of winter for grubs is also generally a good winter for the rest of the garden; harsh cold and dry weather will punish your perennials and shrubs as much as they will punish overwintering insects.
One thing that most insects will agree upon is that mild winters are very helpful. Mild winters usually mean a greater incidence of pest issues the following season due to higher insect populations.
Ask a Rabbit (or a Rhododendron)
If you were to ask a rabbit or deer what kind of winter they would like, you would get a very different answer. Rabbits and deer have more difficulty finding food when there is heavy snow cover because some of their winter snack food is buried! Rabbits and deer are content to forage on the bark of young, woody plants. When young plants aren’t accessible due to deep snow, they are forced to subsist by chewing the bark off of larger plants.
Deer and rabbits would prefer a mild winter where the bulk of the precipitation is rain rather than snow, which, coincidentally, is also a great winter for many ericaceous plants like Rhododendrons and Japanese Andromeda.