The bitter winter air smacks you in the face as you quickly move about your business. Piles of snow, now more gritty and dirty than freshly fallen, still cover the landscape.
Mother Nature has held us in her icy grip, lashing out with a force we haven’t seen for decades. Winter, it seems, has come with a vengeance.
While the bitter cold of winter can inconvenience us with frozen pipes and over-worked furnaces (both of which I dealt with), it can also deal an icy blow to the garden. There are several types of damage that plants in the garden can experience through winter, each with their own unique symptoms and treatments.
Typically, damage will not be noticeable until the weather warms up enough for the damaged part to thaw out and tissues start breaking down.
Most of the winter damage that we see, especially on both broad-leaved and needle-leaved evergreens, is basically referred to as “winter damage.” This damage doesn’t necessarily come from the cold, though. This damage is most commonly caused by the drying out of the plant.
Cold winter air is especially dry (since any moisture usually condenses and freezes in the form of frost). The dryness is compounded by the usually ever-present wind that blows through winter, which leaches moisture out of plant parts that are exposed to it.
This type of drying out damage will show up as a large section of dead needles or leaves in an area that frequently receives the brunt of winter wind. The damage is usually isolated on the plant unless it is exposed in an open and windy area.
This damage is also made worse if there are bright and sunny days during the cold of winter — the warmth on the leaves makes them lose water through their openings, called stomata.
The best way to prevent this damage is to make sure the plants are well watered in the late fall so that they can take up as much moisture as possible. Frozen ground means that plants can’t pull water out of the ground, so making sure they are hydrated before winter is key. If you know of problem areas, such as naturally windy areas, you may want to wrap trees or shrubs with burlap or a protective cloth to limit wind exposure.
Unfortunately, any area of a needle-bearing evergreen that is completely killed will not regrow. Any completely brown branch of an evergreen plant will have to be removed.
Another type of damage that winter ravages on plants is freezing. Freezing damages plants by causing the water inside their tissues to expand (a property of water).
When the water forms ice crystals and expands, it damages the cell walls of plants, which in turns causes their death. While it isn’t common here in West Virginia, if the temperature drops fast enough and goes low enough, trees can even split or “explode” under the pressure created by the expanding water.
Generally speaking, most plants can withstand the regular cold temperatures in an area where they are considered hardy. If you live in hardiness zone 6 and all of your plants are hardy in zone 6 or lower, you shouldn’t really experience freezing damage under normal conditions. However, there are exceptions.
When temperatures fall below the average coldest temperature reflected by the zone rating, damage can occur. It just so happens that the freezing cold we experienced a few weeks ago was colder than the average dictated by the zone in many areas.
Most of West Virginia lies in hardiness zone 6, which has an average coldest annual temperature between 0 and -10 F. In places that were colder than -10, it is possible to see freezing damage on plants rated even for zone 6.
While these frigid temperatures brought on by shifting jet streams and weather patterns aren’t going to affect the average or the zone rating any time soon, it can cause damage to plants in the meantime. There isn’t much you can do to protect trees and shrubs from freezing other than wrapping them with a protective cloth (and that won’t do much when it is really cold).
Some plants are also not as hardy as others, even when they are rated for a certain zone. For example, crape myrtles aren’t as tough as other zone 6 shrubs when it comes to winter. I will expect lots of damage to crape myrtles, and even maybe total losses. These plants are also likely to be slow to wake up after a cold winter. Leafing out and flowering could be delayed for weeks or even months, so I would suggest waiting a while before pruning out anything that you think is damaged.
You can also check for damage once temperatures warm up by doing a twig test. If you bend a twig or small branch and it is dry and breaks, that indicates that part of the plant is dead. If it springs back, things should be OK.
Freezing can also affect herbaceous perennials that have died back to the ground. Mulching will help reduce the likelihood of damage on perennials. There are some plants, however, that we have gotten used to growing as perennials that should actually be taken up for the winter in most of the area. Things like cannas and gladiolas are less winter hardy and could sustain damage from recent subzero temps.