A frost crack is a vertical crack in a tree that may be up to several meters long. They usually are apparent in the early spring and are most often found on the south or southwest side of a tree.

The south or southwest side of a tree receives more sunlight which warms the bark causing it to expand during the cold winter months. The drop in temperature when the sun goes down causes the layer of bark to cool faster than the wood under it. The bark then splits vertically over the expanded wood causing the frost crack. Frost cracks leave the tree vulnerable for the entry of bacteria, fungi, decay organisms and insects.

Most trees form a callus layer to seal the edges of the wound during the first growing season after the crack appears. The callus layer will continue to grow and the wound may close completely or the wound may continue to split on very cold days.

Protecting trees from frost cracks can be difficult due to fluctuations in temperature and sunlight during the winter months. Tree wraps can be placed around young trees from the ground level to the first main branches, but please remove the wrap in the spring. Always remember to protect trees from physical damage caused by lawn mowers, trimmers and animals.