It looks like winter is here and the temperatures being forecast for this week are certainly going to impress upon us that reality. Like most people who garden, our thoughts turn to how well our plants will survive the bitter cold. The ground is now frozen in most places and the recent snow cover will help moderate the soil temperatures from fluctuating too drastically. Unfortunately the temperatures above the snow can and will change dramatically with the weather. If the plants in the garden have been chosen for hardiness in your area, and enter the fall healthy, then in most cases all should be fine. What is interesting is how they endure the cold. Understanding the adaptations that plants ( and animals) go through to survive living in a cold climate, has always fascinated us. If you reside in the North, you have to have strategies for surviving these extreme temperatures.
While not growing, the plants cells are actually active during winter. The plants hardiness is determined by its ability to adjust the chemical combinations within its cells. The more they can adjust to the impending cold, the greater the chances for making it through the winter. Lower temps, reduced soil moisture, shorter days, and less nitrogen, are also factors that will increase tolerance to cold temperatures. The plants started the acclimation to cold weather with the shorter days in June, and then again during a second stage initiated after a frost, and will continue to do so even more as the temperature drops. The plant cells are trying to keep themselves from freezing to the point of rupturing and damaging the cell membrane. The way they do this is by moving water out of the cell itself and storing it in spaces between the cell walls. Ice formation inside the cell membrane is fatal. Within the cell, the concentrations of sugars, organic acids, and water soluble proteins are modified to prevent the water that is still in the cell from freezing. A bit like plant anti-freeze. The colder it gets, the more they adjust. More water out, results in higher concentrations of solutes inside, and a lower freezing point for the cell. In some relatively rare cases, a prolonged warm period in winter can have the cells bringing more water into them. If the temperature should drop rapidly, the cells may not be able to remove enough water fast enough to prevent ice from forming within them, resulting in damage to the plant. This might explain the winter damage to woody plants after what may have seemed like a relatively mild winter.
We go out everyday to tend the animals, bring in firewood, and shovel snow here at the nursery. We’re outdoors a lot. We are well aware of how quickly these below zero temps can cause discomfort or even frostbite ( or hypothermia), if we don’t dress appropriately. Wearing wool, a down vest, and good insulated boots are just a few of the adaptations we humans have for tolerating the cold. Again, once you start uncovering some of the behavioral or structural adaptations of the plants and animals here in the north, you begin to really appreciate how fine tuned and effective those adaptations have to be. Life depends on it. That being said, time to head out to the chicken coop to collect eggs before they freeze solid. 
Once the nursery season is officially over, we wait for the temperatures to be consistently cold in order to cover plants in the retail and stock area. This is somewhat tricky on account of the fluctuating weather we may experience in the fall here in Maine. Many of the plants we over-winter are lined up and then covered in a specially designed winter ‘blanket’. Our ideal is to have the plants freeze and remain frozen, it’s the freeze-thaw-freeze-thaw that we’re most concerned about.
Fernwood Nursery & Gardens 