Frost cracks in trees
Bitterly cold conditions in winter can cause thin-barked trees to crack.
Subzero weather is hardly anyone’s favorite time to look for problems in the landscape. Often we do not see damage that happens over winter until spring. Below zero temperatures can create some unique problems for landscape plants. One such problem, frost cracks, can permanently damage trees. Very low temperatures in Michigan this winter have left some trees with vertical cracks. These longitudinal openings referred to as frost cracks can extend deep into the wood of the tree. Certain trees tend to be more prone to this disorder. Most commonly it is seen in sycamores, but it also occurs in maples, apples, cherries, horse chestnuts, lindens, walnuts and willows.
Frost cracks are often found on trees that are out in the open where sun shines directly on the bark. Cracks are first initiated on a winter’s day when sunlight warms the bark and inner wood on the south or west side of the tree, especially on young trees with thin bark. As the sun sets or is hidden by clouds, the temperatures drop quickly causing shrinkage in the bark while the inner wood takes longer to contract. This unequal shrinkage or contraction between the bark and the inner wood causes the bark to split and along with it the wood directly below the bark. Scientists believe it actually results from water moving out of cells and freezing during sudden drops in temperature. The wood closest to the surface shrinks as water is lost quickly while the inner wood is not affected. The sudden change creates pressure between these two zones resulting in the wood cracking. The sudden splitting causes a loud report or bang.
Old sycamore trees that are wounded when young by this type of injury can have cracks that reopen each winter during periods of extreme cold. A sycamore on the campus of Michigan State University had a frost crack wide enough to fit your hand well into the wood in the winter and when weather warmed, it would close. Over time these wounds may develop a raised area where callus tissue develops, attempting to close over the wound.
The Michigan State University Extension garden hotline has received calls on frost cracks over the winter. Homeowners contacting the hotline at 888-678-3464 were concerned on what they could do to help their trees. Once cracks have occurred in the bark, there is not much that can be done. As weather warms, these cracks close over, but can still be an entry point for decay fungi and also insects. Smart Gardening practices that focus on maintaining plant vigor such as watering during droughty conditions, alleviating compacted soils and fertilizing trees that have poor growth can help to prolong the life of the damaged trees.