Used by permission. Written by Faith Appelquist in December newsletter of Tree Quality
I received a question this week on the benefit of wrapping trees to prevent winter injury, specifically the splitting of trunks. This splitting is either due to a frost canker or a frost crack. Frost cankers and cracks on ornamental trees; wrap or don't wrap?
A frost canker, sometimes called sunscald, is a shallow split in the bark and forms as a result of extreme temperature fluctuations. While these cankers are more common on the southwest side of the tree, they can occur on any side of the trunk. The problem occurs when tissue that is beginning to lose its cold hardiness is exposed to cold temperatures during late winter nights. The tender bark and cambial tissue are killed. This is most common on thin-barked trees such as fruit trees, lindens and maples, but is also stress-related. Moisture stress during the summer and fall is most often correlated to frost cankers occurring that winter. Trees that are planted too deep may also develop frost cankers.
Frost cracks, on the other hand, are deep, longitudinal cracks that appear on the lower trunks of trees. You can sometimes hear gunshot-like reports in the woods in winter as a tree suddenly cracks open. On cold nights the outer part of a trunk freeze-dries in the same way that unwrapped food desiccates in a freezer. As it dries and contracts over the still-wet center, the pressure is eventually relieved by the wood cracking open. In the spring, the crack closes and the new wood formed that summer papers over the crack, but this may not be strong enough to resist cracking next year. Several mild years are usually needed to build a strong enough bridge over the crack to prevent future cracking. Tree species such as oak crack more than others, but no species appears to be immune. Some experts see the cause of frost cracks in earlier stem injuries, such as pruning wounds, which can initiate cracking when freeze shrinkage and ice expansion generate tension stress.
Will wrapping trees during the winter help? Will painting the trunk white help? It might, but keep in mind that moisture stress and wounding are the two key factors in the formation of cankers and cracks. Wrapping with paper or plastic wrap may not prevent temperature fluctuations; in fact it may actually cause a more rapid temperature change. In addition, if the wrap is left on into the next growing season it may trap moisture, creating a favorable habitat for pests. Left on even longer it can girdle the tree.
Wrap or don't wrap? I say "Don't" since the problems of leaving it on too long outweigh the small benefit of winter protection; but do make sure the trees are receiving adequate water during the growing season and do not wound the trunk. These are best means to reduce frost cankers and cracks.
For more information on frost cracks and sunscald.
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More on winter injury on trees
I received a question this week on the benefit of wrapping trees to prevent winter injury, specifically the splitting of trunks. This splitting is either due to a frost canker or a frost crack. Frost cankers and cracks on ornamental trees; wrap or don't wrap?
A frost canker, sometimes called sunscald, is a shallow split in the bark and forms as a result of extreme temperature fluctuations. While these cankers are more common on the southwest side of the tree, they can occur on any side of the trunk. The problem occurs when tissue that is beginning to lose its cold hardiness is exposed to cold temperatures during late winter nights. The tender bark and cambial tissue are killed. This is most common on thin-barked trees such as fruit trees, lindens and maples, but is also stress-related. Moisture stress during the summer and fall is most often correlated to frost cankers occurring that winter. Trees that are planted too deep may also develop frost cankers.
Frost cracks, on the other hand, are deep, longitudinal cracks that appear on the lower trunks of trees. You can sometimes hear gunshot-like reports in the woods in winter as a tree suddenly cracks open. On cold nights the outer part of a trunk freeze-dries in the same way that unwrapped food desiccates in a freezer. As it dries and contracts over the still-wet center, the pressure is eventually relieved by the wood cracking open. In the spring, the crack closes and the new wood formed that summer papers over the crack, but this may not be strong enough to resist cracking next year. Several mild years are usually needed to build a strong enough bridge over the crack to prevent future cracking. Tree species such as oak crack more than others, but no species appears to be immune. Some experts see the cause of frost cracks in earlier stem injuries, such as pruning wounds, which can initiate cracking when freeze shrinkage and ice expansion generate tension stress.
Will wrapping trees during the winter help? Will painting the trunk white help? It might, but keep in mind that moisture stress and wounding are the two key factors in the formation of cankers and cracks. Wrapping with paper or plastic wrap may not prevent temperature fluctuations; in fact it may actually cause a more rapid temperature change. In addition, if the wrap is left on into the next growing season it may trap moisture, creating a favorable habitat for pests. Left on even longer it can girdle the tree.
Wrap or don't wrap? I say "Don't" since the problems of leaving it on too long outweigh the small benefit of winter protection; but do make sure the trees are receiving adequate water during the growing season and do not wound the trunk. These are best means to reduce frost cankers and cracks.
For more information on frost cracks and sunscald.
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More on winter injury on trees
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