One of the prominent concerns of Northern gardeners, especially this time of year, is understanding the concept of winter hardiness. Answering the question “Will my perennial plants or bushes survive the winter?” is no easy task.
Take the field of strawberry plants my husband and I planted when we had the greenhouses … The plants that received a mulch of straw didn’t survive, whereas the plants without mulch, did.
Each species of plant has a built-in threshold of tolerance to low winter temperatures, and we know that some plants are hardier than others. We know that if we choose plants that are rated for our growing zone, we can expect them to survive a winter.
But there are those of us who want to push the limits – to grow plants and bushes that are, by the strict numbers of hardiness, supposed to be impossible to grow here. We all know someone who was successful in growing plants that shouldn’t grow in our zone. We wonder what new skills or tricks they have that we are not aware of.
There are numerous ways of pampering plants to increase their chance of survival in a hardiness zone where they would otherwise not survive: adequate shelter, protection from wind, peat-moss mulching and snow cover are some of the ways by which we can extend the hardiness of a specific plant and encourage it through the winter.
Hardiness zones do not take into account snow cover. Snow acts as an insulator against extreme cold temperatures, therefore protecting the root system of plants.
If the snow cover is present before the really cold days, the actual temperature to which the roots are exposed is not as low as the air temperature; therefore, some “out of zone” plants may survive and only suffer winter injury on exposed branches and stems.
In the grey area of hardiness and non-hardiness, often you will find that winter damage and survival becomes a matter of probability. In warmer winters, the plant may survive, while in colder, windy winters it may suffer considerably or even die.
Often, it is a matter of risk and a willingness to understand the specific needs of a plant to give it the best chance of winter survival.
Do realize that each and every specific plant varies within a range of winter hardiness that depends on other factors. It is not possible to say that a plant will die at -42, but will survive at -41.
If the health of the plant, going into the winter, is excellent, characterized by adequate watering, no drainage problems, proper amount of sunlight, soil fertilizer, etc., the plant may survive -45 or -50. But, by the same token, if it is not a “happy” plant or bush, it may not even survive -35.
If the various growing needs of a plant are met every year, you stand a better chance of stretching the hardiness zone of plants.
This is nothing more than acquainting yourself with each plant’s preferences, its likes and dislikes, its soil requirements, its degree of wind protection, its water tolerance and then providing these conditions each year.