Calgary's winters test every tree on your property. It is not just the cold, though minus 30 is plenty cold. It is the combination of extreme cold, dry air, heavy wet snow, chinook temperature swings, and road salt that makes our winters uniquely challenging for urban trees. Most winter tree damage is preventable if you know what to watch for and take action before the snow flies.
Snow and Ice Loading
Heavy, wet snow is the most common cause of winter tree damage in Calgary. When a dump of wet snow lands on a tree with leaves still attached, or on evergreens with their full needle load, the weight can snap branches, split crotches, and even topple entire trees. The September and October snowstorms that catch trees before they have fully dropped their leaves are particularly destructive.
Prevention starts with structural pruning during the growing season. Trees with a single, well-defined leader and properly spaced scaffold branches handle snow loads far better than trees with co-dominant stems, tight crotch angles, and overcrowded canopies. If you have a tree with structural weaknesses, have it assessed and pruned before winter.
For multi-stemmed trees and upright evergreens that are prone to splaying under snow, cabling systems provide permanent support. A flexible steel cable installed between the main stems prevents them from spreading apart under load while still allowing natural movement. This is a professional installation that provides years of protection.
Frost Cracking
Frost cracks are vertical splits in the trunk bark that occur when rapid temperature drops cause the outer bark to contract faster than the inner wood. They are most common on the south and southwest sides of trunks, where winter sun exposure creates the greatest temperature differential. In Calgary, chinook conditions — where temperatures can swing 20 degrees or more in a single day — make frost cracking especially common.
Once a frost crack forms, it tends to reopen every winter and gradually enlarge. While frost cracks rarely kill trees directly, they provide entry points for decay fungi and weaken the trunk structure over time. Young trees with thin bark are most vulnerable. Wrapping trunks with commercial tree wrap or white plastic spiral guards reflects sunlight and reduces the temperature swings that trigger cracking.
Sunscald
Closely related to frost cracking, sunscald occurs when winter sun heats the bark on the south side of a trunk to the point where cells become active, then freezing temperatures return and kill those activated cells. The result is a dead, sunken patch of bark that eventually peels away, exposing the wood underneath to decay.
Sunscald is most common on young, thin-barked trees like maples, mountain ash, and newly planted specimens. The prevention is the same as for frost cracking: wrap the trunk from the base to the first branch with light-coloured tree wrap in late fall and remove it in spring. Established trees with thick bark are generally resistant to sunscald.
Winter Desiccation
Evergreen trees continue to lose moisture through their needles all winter, even when the ground is frozen and they cannot take up water through their roots. If the tree entered winter with a dry root zone, or if winter conditions are particularly dry and windy, the tree can lose more moisture than it can replace. The result is brown, dead needles that appear in late winter or early spring, often on the side of the tree that faces the prevailing wind.
Prevention is straightforward: water evergreen trees deeply in late fall, just before the ground freezes. One thorough soaking puts moisture in the root zone that the tree can draw on throughout winter. If chinook conditions melt the surface in midwinter and the ground briefly thaws, water again. Mulching the root zone helps retain this moisture and moderates soil temperature.
For evergreen hedges and specimens in exposed, windy locations, burlap screens can reduce moisture loss by blocking wind. Install the burlap on stakes around the windward side of the tree, not directly on the foliage, to allow air circulation while breaking the drying wind.
Road Salt Damage
Trees planted near roads, driveways, and sidewalks that receive de-icing salt face a specific winter hazard. Salt spray coats branches and needles, causing direct tissue damage. Salt dissolved in snowmelt infiltrates the soil and damages roots, disrupts water uptake, and alters soil chemistry. The effects of salt damage often do not appear until spring or summer, when affected trees show brown foliage, stunted growth, and die-back on the side facing the road.
If you have trees near salted surfaces, there are several strategies to reduce damage. Use salt alternatives like calcium magnesium acetate or sand on your own property. Create physical barriers like snow fences or burlap screens between the road and vulnerable trees. In spring, flush the soil around affected trees with heavy watering to leach accumulated salt out of the root zone. Over time, consider replacing salt-sensitive species near roads with more tolerant ones like bur oak or green ash.
Rodent Damage
Mice, voles, and rabbits feed on tree bark during winter when other food sources are scarce. They work under the snow line, so you may not notice the damage until spring when the snow melts to reveal a ring of chewed bark around the base of the trunk. If they girdle the tree — removing bark all the way around the circumference — the tree will likely die because the connection between the roots and the canopy has been severed.
Protect young trees with plastic spiral guards or hardware cloth cylinders around the base of the trunk. Extend the protection high enough to account for expected snow depth, as rodents will chew at the snow surface level. Keep mulch pulled back from the trunk slightly to eliminate hiding spots, and remove tall grass and debris from around the tree base in fall.
Planning for Next Year
The most effective winter damage prevention happens during the growing season. Structural pruning in summer and fall removes hazardous branches before they become laden with snow. Deep watering in October ensures adequate moisture reserves. Wrapping and guarding in November protects vulnerable bark. Each of these steps takes a small amount of time and effort but can prevent damage that costs hundreds or thousands to repair.