Protect your Trees during Winter Drought

Many parts of Alberta are under drought conditions since June of last year. Severe droughts cause widespread tree mortality across all landscapes (urban, acreages, farms, municipalities, and the province) with profound effects on the function of forestry ecosystems and the overall environment. As the drought we experienced during the summer and fall continued into winter, with no snow on the ground to protect root systems, we continue to see tree roots suffering from winter drought and sustaining physical damage. 

Cold winter damage can happen due to the tree's inability to survive cold weather, lack of snow (as we've experienced in some parts of Alberta, strong cold and dry winds, and heavy snow and ice in late fall or early spring. As winter casts its dry cold and icy spell, trees face a unique set of challenges, especially in regions already experiencing drought.

Winter drought, characterized by a scarcity or lack of water insulation and snow protection to roots during the colder months, poses a threat to the well-being of trees. Despite the leafless appearance and their apparent dormancy, trees are engaged in a complex dance of survival during this period. Roots remain mostly inactive but can, and do, function and grow during winter months when soil temperatures are favourable, even if the air above-ground is brutally cold. 

Unlike the more conspicuous summer drought, winter drought often goes unnoticed, as the ground may appear frozen and devoid of visible signs of moisture scarcity. However, trees and their roots continue to lose water through transpiration, albeit at a slower rate than during the growing season.

It is important to note, that newly planted trees are at a higher risk of sustaining injuries from the winter cold compared to mature trees. Additionally, during the winter months coniferous trees might lose water through their needles faster than their roots can absorb, resulting in brown needles during the spring. This occurrence is known as winter browning in coniferous trees. 

Trees, Root Health, and Preservation

Root injuries resulting from cold conditions pose a significant threat to the vitality of trees and shrubs. Roots do not enter dormancy simultaneously, in contrast to branches, buds, and trunks. Research indicates that roots continue their function and growth during winter, especially when soil temperatures remain favourable, however; the physical effects of freezing, heaving, and soil cracking can cause substantial harm to roots, particularly the delicate feeder roots in the upper layers of organic material. Preserving the roots is of paramount importance. 

Mulching: As many parts of Alberta are experiencing no, or very little, snow, mulching now, from January to March, can still be beneficial to protect the roots of your trees. Mulching is a fundamental practice to shield roots, and is a simple yet effective strategy to protect trees during winter drought. A layer of organic mulch around the base of the tree helps retain soil moisture, insulate roots from extreme temperatures, and suppress weed growth that can compete for water. Applying 4-6 inches (10-15 cm) of arborist wood chips will greatly reduce the loss of moisture in the soil. Establishing a donut-shaped wood chip cover around your tree is an effective approach to conserve moisture and minimize soil frost heaving.

Snow Fences: Snow fences are effective physical barriers that also double as windbreaks. Positioned strategically on the windward side of a tree or grove, they slow down the wind, reducing its intensity before it reaches the trees. 

Hay and Straw Bale Barriers: For newly planted or young trees, establishing a row of hay or straw bales (large or square) around them will protect the trees from cold and strong winds. 

Windbreak Walls: Constructing windbreak walls involves erecting solid structures, such as wooden or plastic panels, aimed at intercepting and deflecting cold winds away from trees. These walls are strategically placed to create a barrier that minimizes the force of the wind. 

Snowfall Advantages: Snowfall is beneficial to trees as it helps prevent the soil from freezing, even in severely cold temperatures. If snow arrives after the soil has already frozen, it acts as a protective layer, shielding roots from temperature fluctuations during thawing periods, from January to March. 

Examine and Seal Cracks: For recently planted trees, inspect the soil for cracks resulting from the planting process or dry fall conditions. Sealing cracks prevents cold air from infiltrating the soil. Alternatively, adding adequate mulching can also serve this purpose. 

Avoid Pruning or Other Physical Damages: It is important not to damage trees and roots during this period. Avoid pruning, physical damage, or driving around the root zone. 

Wildlife Protection: Use mesh wire, 1/4 (quarter) inch in size, to protect trunk bark from mice, rabbits, voles, deer, and moose. Adding plastic guards around fruit trees will also protect the bark from sunscald, as well as any stripping by moose or deer. 

Avoid Salt Damage: Avoid or reduce the amount of salt used for de-icing around trees and shrubs. 

Prepare Trees: Prepare your trees for early spring and recovery once weather conditions become favourable, by watering, fertilizing, and removing dead branches. 

In the face of persistent drought, cold winter winds, and lack of snow, implementing physical barriers, adding mulch, and avoiding salt use are the only proactive and effective strategies to protect trees.