Frost cracks occur when air temperatures fluctuate below and above freezing or when sunlight warms a tree up in the daytime before the tree refreezes at night. When the moisture in the outer layers of a tree melts and then quickly refreezes, the rapid expansion of the ice breaks the outer layer of wood and bark, resulting in a (usually vertical) split. Bark is a tree’s natural protection, and broken outer bark exposes the sensitive inner layer of fresh, actively growing wood.

Frost cracking generally affects the trunk of a tree, particularly in the lower to middle sections where much of the tree’s moisture is stored. A frost crack can be anywhere between a couple of inches to several feet, depending on the size and type of tree. Some of the factors that affect a tree’s vulnerability to frost cracking include the type of bark a tree has, the species of tree, and its age.

Trees with thin bark, such as maple, birch, black cherry, elm, and sycamore, are more susceptible to the thaw-and-freeze cycle. Trees with particularly thick, textured bark, like oak, chestnut, and many evergreen trees, are more tolerant of temperature fluctuations.

Young trees of all species are more at risk of cracking in temperature fluctuations than mature trees due to their thin, smooth bark, small trunk size, high moisture content, and lack of root establishment.