Winter presents unique challenges for trees, even when dormant, subjecting them to environmental stresses that can compromise their overall health. The most significant threats are desiccation, extreme temperature fluctuations, and mechanical damage from weather events. Trees lose moisture through their bark and needles, but frozen ground prevents roots from replenishing water. This leads to desiccation, often called winter burn. Preparing trees proactively before the cold weather sets in mitigates these risks and ensures survival and vigorous growth in the spring.
Preparing the Root Zone and Soil Moisture
The health of a tree’s root system is the first line of defense against winter stress, making pre-winter hydration a fundamental task. Evergreens are particularly susceptible to desiccation because they retain their foliage and continue to lose water through transpiration throughout the winter. Deep “winter watering” or “fall soaking” should be performed until the ground freezes, ensuring the roots have a significant reserve of moisture to draw upon. This watering should be done when temperatures are above 40 degrees Fahrenheit and the soil is thawed, focusing on the area beneath the tree’s drip line where the absorbing roots are located.
Proper mulching regulates soil temperature and retains the moisture supplied during the fall. Apply a layer of organic mulch, approximately two to four inches deep, from the trunk out to the drip line. Leave several inches of space directly around the trunk, creating a “donut” shape, to prevent moisture retention that can lead to bark decay or fungal pathogens. Avoid late-season fertilization entirely, as this encourages tender new growth that lacks the hardiness to survive freezing temperatures.
Safeguarding Trunks Against Sun Scald and Rodents
Sun scald is a specific type of injury that occurs on the south or southwest side of thin-barked trees, especially young ones, during winter. On bright, sunny winter days, the dark bark absorbs solar radiation, causing the underlying tissue, the cambium, to warm and become active. When the sun sets or is blocked by a cloud, the temperature of the bark rapidly plummets, causing the tissue to freeze quickly. This results in cracked or sunken areas of damaged bark, which provides entry points for insects and disease.
Protection against sun scald involves applying a reflective barrier to the trunk to stabilize bark temperature. One practical solution is to paint the trunk with a mixture of white, interior flat latex paint diluted with an equal part of water. The white color reflects sunlight, preventing the bark from overheating. Alternatively, use a white or light-colored, breathable tree wrap, applied from the base up to the first set of branches in late fall and removed in early spring.
Protection from gnawing pests like voles, rabbits, and deer is also necessary, as they often target tree bark for food when other sources are scarce. These animals can girdle a young tree by chewing the bark completely around the circumference, which severs the vascular system and leads to the tree’s death. A durable physical barrier, such as a plastic tree guard or a cylinder of wire mesh, should be placed around the trunk. The barrier must extend high enough to prevent damage from animals reaching up on the snowpack, and the base should be secured or lightly buried to block burrowing rodents.
Structural Protection from Ice and Snow Load
Heavy snow and ice accumulation pose a significant mechanical threat, especially to multi-stemmed or densely branched evergreens like arborvitae and juniper. The excessive weight can cause limbs to bend, split, or break entirely, particularly at weak branch unions. Before the onset of winter, preemptive structural pruning to remove dead, diseased, or weak branches reduces the potential points of failure under a heavy load.
If a tree is covered in fresh snow, gently remove the accumulation to prevent breakage, exercising caution. Use a long pole or broom to push the snow off the branches with a gentle, upward motion. Never attempt to shake or strike the branches, as this can cause brittle, frozen wood to snap. If branches are coated in ice, leave them alone, as attempting removal will likely cause more damage than the ice itself.
For vulnerable species, temporary bracing or tying can prevent splaying damage, particularly in the case of shrubs or narrow evergreens. Soft, flexible materials like nylon stockings or specialized tree ties can be used to gently wrap the canopy, holding the branches closer to the trunk. This reduces the surface area exposed to snow and ice. After a storm, any broken or hanging limbs should be removed immediately for safety, though larger structural damage may require assessment and professional removal by a certified arborist.