Winter Garden Concerns
Unseasonably low temperatures within the next couple of weeks will damage plants that are not fully “hardened-off” or those that are marginally hardy. This is particularly true in our area of unreliable snow cover. Gardeners cannot be guaranteed the insulating protection of snow.
Other situations that might cause havoc on plant health this winter are a quick thaw in January or February resulting in flooded areas over the frozen soil. A quest to keep roads and paths clear of snow and ice means that mountains of salt and sand are spread each winter. Heavy snow is another concern. Evergreen trees laden with snow may look picturesque but early season, waterlogged snow could bend the branches leaving them permanently misshapen. Wind scorch is an unappealing sign of the harshness of winter, but it is one of the less damaging factors. A more serious concern is the damage caused by mice gnawing on tender plant stems. This is usually not noticed until plants are struggling to grow the following season.
Preventing damage due to low temperatures is often beyond the control of gardeners. Fluctuations below the annual average low temperature are to be expected during most winters. Gardeners can only hope that their plants have hardened off or are protected in a microclimate and will be able to withstand an early cold spell. Plants are better able to survive if there has been a gradual decrease in temperature instead of a sudden sharp drop. To have reliably hardy plants that are not damaged by low temperatures, select plants that can grow in temperatures that are 2 hardiness zones colder than your garden’s zone. This is wise advice, but it is hard to follow. There are so many exciting marginally hardy plants that make tempting the fates of nature hard to resist. Identify microclimates in your garden where these tender plants can have a bit of protection from the winter weather. A building or evergreen hedge can create such a microclimate.
The January thaws have a positive psychological effect on humans, but are deadly for some plants. The freezing and thawing cycle caused by daytime temperatures above 0 degrees C. and freezing nighttime temperatures is hard on many perennials and some thin-bark trees. Plant tissues expand during the day and contract during the night. For thin-bark trees like the London plane tree, this causes a split in the bark on the southwest side. Often this repeated freezing and thawing prevents the split from healing until spring arrives. For perennials that grow from a crown or are newly planted, the freezing and thawing action might heave them out of the ground. This will leave them exposed to the drying effects of the sun and wind. Inspect your garden during the January thaws and gently press plants back into the soil.
A less frequent injury caused by the winter weather is flooding damage. This is often a short-term problem in late winter when the ground is still frozen and the first heavy rains arrive. Many low-lying areas can be filled with standing water for days. Healthy plants are able to withstand a limited amount of flooding. During late winter, trees are still dormant and little oxygen is exchanging through the roots. A short duration of flooding should not harm them. Willows, bald cypress and alders are more resistant to flooding damage.
Wet, heavy snow is a potential problem at the beginning and end of the winter. This type of snow can cause damage to evergreens or hedges. These plants that do not have strong stems to withstand the weight of snow or because of their shapes, do not shed the snow as it piles up. Boxwood that has not been trimmed is especially prone to snow-load damage. Heavy snow or ice will force the branches downward and leave gaping holes in the shrub that might be permanent. Some cedars (Thuja) and pencil point type junipers might also be damaged. Snow loads could also damage hedges that have been trimmed with a flat top. Minimize the amount of horizontal surfaces that are present on weak-stemmed hedges. Creating a slight angle on the sides is an excellent solution to this problem. To prevent snow-load damage on upright plants, support the branches with fine netting or tie up the plant like a Christmas package with garden twine. In many cases, a broom will work to remove the snow before it becomes heavy enough to weigh down the branches.
The cold, drying winter winds can damage some broad-leaf evergreens, especially Mahonia (Oregon grape). Winter weather causes browning of the outer edge on exposed leaves. In the spring the plant will send out new growth to cover this browning, but it looks bad for a time. Other conifers such as those with golden-coloured foliage and dwarf Alberta spruce might also suffer browning from drying winds and sun during the winter. Plant these in a location where they receive protection from the south and west, use an anti-desiccant spray, wrap them with burlap, or live with the temporary discolouration.
So what can be done to battle the latest weather anomaly? Pretend that the garden has been transported to England or change the calendar to April? The best action is to prepare plants wherever possible for the winter. Hill roses, mulch perennials, and line with burlap where it has been done in previous years. A little effort to give some protection will be well worth it.