Winter weather brings harsh conditions to trees, especially new ones. Mature trees can usually handle winter conditions, however, due to years of growing resistances or existent genetic cold hardiness. The key to winter protection of young trees is preventative measures and selecting varieties that are cold hardy.
Little can be done once cold, ice, and snow injuries occur in young trees. Some can easily die from the extremes of winter. Although, many regions of the world are free of such damaging conditions.
Conditions like frost cracking, sun scalding, evergreen discoloration, winter die-back, and frost heaving can cause very damaging effects on young trees. Ice, snow, and salt are also very detrimental to young trees. Preventing such injuries ensures that young trees will mature and grow for many years while providing aesthetic enjoyment.
A split trunk caused by frost crack.
What Is Frost Crack?
Frost crack is a form of abiotic damage usually found on thin-barked trees on the southerly facing surfaces. Frost cracks are frequently the result of some sort of damage or weakness in the bark that occurred earlier in the tree’s life. Water in the phloem and xylem layers (water transport layers below the bark) expands and contracts during late winter and early spring. Severe cases of frost cracking splits the trunk of the tree and not just the bark and soft tissue layers. Frost crack is similar to sun scalding, but the symptoms are usually much more severe.
Fluctuating winter temperatures are the most apt to produce frost cracks within trees. Damaged bark and wood does not contract the same way that healthy tissue does. Sun heats the bark and the crack occurs when temperatures remain very cold or plummet. Sunny days with clear skies and cold temperatures are ideal conditions for frost cracking.
A loud cracking sound can sometimes be heard when the bark can no longer withstand the contraction of cold temperatures.
Frost crack is preventable with careful thinking and winter tree wraps. Do not fertilize late into the season. New growth may begin after an application of fertilizer. Young growth is more susceptible to frost cracking when compared to mature trees. Protect young trees from physical damage, such as lawn mower and grass trimmer nicks, bad pruning techniques, grazing animals, and any other situation that could contribute damage to the bark. Putting segments of corrugated plastic drain pipe around the trunks of young trees helps prevent trimmer and mower damage.
Tree wraps help prevent frost cracks via insulation and reflection. The material used for the wraps helps to insulate the trunk from excessive warming due to direct sunlight, and wraps reflect a little sunlight as well. Wrap the trunk in late fall, and remove the wrap in early spring. Failure to remove the wrap in spring can cause injury.
Careful placement of new trees can prevent frost cracking by planting in areas that have winter protection. Wind breaks, structures, fences, and other plants can help protect trees that are susceptible to frost cracking. Avoid planting trees in open areas where the sun shines directly onto the trees.
Trees damaged by frost cracks will attempt to seal the edges of the cracks by growing callous layers. The split edges will begin to callous during the spring. The wound may or may not close after many years. A calloused wound can easily reopen during winter if the conditions for frost crack are prevalent.
What Is Sun Scald?
Sun scald and frost cracking are similar, but the former is generally less severe. It can occur at any time of the year, but damage caused during the winter is usually the most severe. Damage may not be noticed immediately after scalding has occurred. Sunken, discolored bark, with cracking and peeling may not be noticed until new growth occurs during the spring. Quick drops in temperature can result in rapid freezing and death of the developing inner bark tissues, especially if frost and freezing temperatures occur during early autumn and/or late spring when growth is still active.
Sun scald damage rarely kills a tree, but excessive and repeated damage to a young tree that is a few years old may cause enough damage that a replacement tree is a feasible option. Sun scald wounds allow insects and organisms access into the tree, which can accelerate decomposition and disease.
Susceptible Species to Sun Scald
Ash , oak, maple, birch , willow , linden , honeylocust, and most fruit trees are susceptible to sun scalding. Although, any newly planted tree can be injured by sun scald if grown under poor conditions.
Wrap the trunks of young trees with tree wraps to help prevent sun scald injury. The material used for the wraps helps to insulate the trunk from excessive warming due to direct sunlight. Wrap the trunk in late fall and remove in early spring. Failure to remove the wrap in spring can cause injury and/or promote disease.
Repair Sun Scalds
Trees that have been scalded will normally heal through growth of the inner bark where the split exists. A sharp, sterilized knife can be used to remove loose bark from the area of the split, which increases the healing process of the scald. The resulting bare patch on the trunk should be left untreated. Do not use paints and tars on the wound. Encourage growth with spring fertilizer applications if the tree shows signs of nutrient deficiencies. Remember to provide adequate water in dry weather as well.
Evergreen Discoloration in Winter
Evergreens can lose their color during winter if exposed to regular wind and bright sun.
Sun and Wind Desiccation
Desiccation occurs when moisture is drawn out of the foliage. Discoloration may occur on the windward and/or southerly side of evergreens. The majority of the tree may discolor if entirely exposed to desiccating conditions.
Temperatures that heavily fluctuate between daytime and nighttime can kill the chlorophyll in evergreens and cause a bleached appearance. Chlorophyll is inactive slightly below freezing, but warm daytime temperatures can activate it. The active chlorophyll and cells can easily be killed when nighttime temperatures plummet.
Frosts in early autumn or late spring can kill evergreen foliage. This occurs because the plant is not yet hardened for such temperatures. Early autumn freezing causes damage, because the evergreen has yet to prepare itself for winter conditions. Late spring freezing is damaging, because the plant has warmed up and begun preparation for rapid spring growth.
Proper planting locations is the first step in preventing winter injury of evergreens. Arborvitae, yew, and hemlock are a few susceptible evergreens. These types of evergreens should not be planted in locations that are open to southern sunlight. Planting susceptible evergreens near windbreaks like buildings, fences, or natural windbreaks will help prevent dessication.
Burlap barriers can be constructed on the southerly or windward side to protect young trees from winter weather. Evergreens with previous injuries can be surround by a burlap structure similar to a fence. Allow an open top for air and sun though.
Keeping young evergreens watered well during the growing season and into autumn will help prevent desiccation of foliage. Do not water when frost or freezing conditions are in the near future. Anti-desiccant sprays can be applied to evergreen foliage to reduce moisture loss as well.
Trees can lose shoots and buds due to winter weather. Little can be done to prevent winter die-back, but selecting winter hardy varieties of trees will greatly reduce the possibility and damage caused by die-back.
Research hardiness zones and which trees can tolerate colder zones. Plants that experience growth spikes in autumn are not the best when it comes to hardiness. New growth is very susceptible to winter conditions. Plants that are not-so-hardy should be planted in protected areas away from winter winds and snow, or not planted at all. Such plants should not be fertilized in late summer and pruning should occur long before autumn arrives.
Above-ground roots are susceptible to winter damage.
The above-ground sections of young trees may appear to have entered dormancy, but the roots below the soil surface are still active. Roots are more susceptible to winter injury compared to the rest of the tree above ground. Soil temperatures usually remain relatively warm underground, even during harsh winters.
Preventing Winter Root Injuries
Young, transplanted trees require the hole backfilled properly with soil native to the planting location. No pockets of air should remain in the backfilled area. Pockets of air can expose the roots to cold temperatures and the roots may freeze and die. Fill cracks and spaces to prevent such injury.
Adding 6 to 8 inches of mulch on the soil surface around the tree trunk will help to protect against root injury also. Be sure not to pile mulch up and onto the trunk. The trunk should be surrounded by a "donut" of mulch instead of a cone of mulch. Mulch piled around a trunk can damage the bark and cause the trees to become susceptible to disease and injury.
Snow and Ice Damage to Trees
Heavy snow and ice storms can snap branches and split the crotches of trunks. Wood and bark becomes stiff and brittle during the winter, and significant weight from ice and snow will easily break limbs.
Young trees that have multiple leaders/trunks, like upright junipers and arborvitae, can be bound together with nylon straps, strips of carpet, cloth, or nylon stockings. The chosen material should be tied two-thirds of the way above the weak point. The material needs to be removed in the spring to prevent damage when the tree begins growing again. Professional arborists are needed for large trees with wide-spreading limbs and leaders.
Salt and Deicer Damage
Salt and deicing solutions are harmful and can easily kill trees no matter what age the tree is. Salt runoff is absorbed by roots, and passing cars can splash runoff onto foliage and bark. Do not plant trees in areas that receive salt applications during winter, especially in parkways, road sides, ditches, and next to parking lots. Nothing can be done once a tree has absorbed a significant amount of salt or deicing solution. Some deicers have become more environmentally friendly, but the majority are still harmful to plants.