Protect Your Young Trees this Winter
By Beth Berlin, University of Minnesota Extension
Due to the mild late fall weather there is still time to protect your trees from winter damage. Young, thin skinned trees like maples, linden, honey locust, crabapple, plum, cherry, and apple are susceptible to irreversible winter damage called sunscald if not protected.
Even in a more mild winter the trees mentioned are still likely to suffer winter damage. Damage on these thin barked, young trees can cause cracks, discoloration, splits, and sunken areas. Sunscald refers to the injury to the living cells just inside the bark due to the fluctuation in day to night temperatures in the winter months. Research has shown that the south, southwest facing sides of the tree trunk, specifically the cambium layer, can reach into the 60’s° F, while the north side of the trunk can remain below freezing. The cambium layer is the layer just below the bark that is where cell growth occurs, causing expansion or secondary growth of the tree. The phloem layer is also damaged which is where the water and nutrients are carried throughout the plant. Those warm temperatures trick the tree out of dormancy only to have lethal freezing occur once the sun sets.
Drought also contributes to the extent of sunscald damage. Together they can cause vertical frost cracks and death to the cambium and phloem layers where infection can occur which will cause decay and canker.
The best way handle sunscald damage is to be proactive and prevent the damage from ever occurring. This can be done with complimentary plantings of shrub species or structures on the south and southwest side of the sensitive tree. At this point in the year using light colored or reflective tree wrap is your best option. Current recommendation is to wrap newly planted trees for the first two winters. However wrapping for a couple additional years on sensitive thin barked tree species may be necessary. Always remove the tree wrap in the spring. If it is left on moisture can be trapped and may provide an environment where infection and disease may occur once the weather has warmed.
Tree wrap can be purchased at most garden centers or found online and is reasonably inexpensive. Therefore it is important to spend a little extra money and time for the first several years after planting a new tree that has thin bark to help ensure the health and longevity of it.
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