Frost Cracks In Trees

Those warm spring days with bitterly cold nights can crack your tree trunk. Ever been outside and heard a loud “crack,” looking around for the falling branch but seeing nothing? You may have just heard a tree experience a frost crack. According to the University of Maryland Extension service, spring sun can make tree bark as much as 18° F warmer than the outside temperature, especially on the south/southwestern side of a tree. When the sun goes down and cold night temperatures hit, the outer bark gets cold and can rapidly contract, while the inner bark remains warmer. Bam! The outer bark cracks apart, leaving a vertical gap in the bark. There may be just a little more to it, though, says the Michigan State University Extension, saying it’s water moving out of cells and freezing during sudden temperature drops: “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 cracks are most likely to occur in younger trees that haven’t developed a thick outer bark, although any tree is susceptible.

With young trees, many experts advise wrapping the trunk in burlap to help protect it. Sycamores and trees with thin bark are highly susceptible to frost crack. Types of trees most likely to experience a frost crack include:

 apple
 ash
 beech
 cherry
 crabapple
 horse chestnut
 linden
 maple
 walnut
 willow

Fortunately, even with large cracks, most trees go on about their life without problems. The one thing trees can’t defend against is opportunist organisms like fungi and boring insects who may use a frost crack as a front door to new digs. These invaders can damage your tree. If you see a frost crack, skip do-it-yourself paint-on remedies. With clean edges, the tree trunk will build its own protective layer. “If there is a ragged tear with shredded bark, trim off the affected bark. Then trace around the wound with a sharp, sterile knife,” advises Missouri Botanical Garden. “This cut stimulates cambium growth and speeds healing. A half-inch margin of bark around the wound can also be removed to give a clean edge around the crack. The edges will callus and eventually close over the wound.” For large cracks that concern you, consult an arborist who may be able to bolt the edges together, a process known as “lip bolting.”