As temperatures fluctuate, trees and shrubs can be damaged by freezing and thawing when there are very cold nights followed by warmer sunny days. Most materials shrink as they get colder and expand as they warm. The same is true for soil and for the bark of trees. This is what leads to two common cold-related injuries: frost heaving and winter bark cracking (splitting).
Frost heaving occurs when the upper layers of soil expand during the day as sunlight warms and thaws the surface, and then freezes and shrinks at night when the temperature drops. This constant cycle of expansion and contraction causes the soil to move and crack. This movement can break roots, or can push entire shrubs out of the soil (and also causes pot holes). This type of damage is most common on shrubs and recently planted small trees.
The second way in which expansion and contraction due to temperature fluctuations damages trees is a phenomenon known as frost cracking. This occurs when the bark expands as it warms during the day. Usually the southwest side of the bark warms the fastest and damage is most commonly seen on the south or southwest side. When the sun sets and the temperature drops, the outer layer cools and contracts faster than other portions, resulting in vertical cracking. These cracks can later be colonized by decay fungi, or serve as an entry point for various borer insects.
Understanding how temperature can impact your trees can help you identify potential issues before they become serious.
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