---

They look shocking and mysterious and certainly take away from an otherwise beautiful tree, but there isn't much mystery to what causes Frost Cracks or Frost Cankers and in fact, we the homeowner, may well be contributing to this malady and not even know it.

Frost cankers - a.k.a. sun scald - may appear as longitudinal splits on the south or southwest sides of the bark along the main stem or branches, or simply as sunken dead areas. Practitioners speculate that cambial tissues are damaged when trees begin coming out of dormancy and are subjected to sudden temperature changes in the late winter/early spring.

Frost Cracks are formed during extreme winter temperature fluctuations (i.e., when temperatures plummet to say below 15 degrees at night) and can be found on any side of the stem or branch. These are similar to frost cankers in that they are longitudinal; however, a true frost crack extends into the stem's wood.

Native Americans called February the "Night of Popping Trees" for the loud sound that could be heard as Aspen trees experienced sudden cracking.

Maples are often mentioned as trees susceptible to Frost Crack/Sunscald, but in fact transplant stress, and, more importantly water stress caused by root loss during transplanting may be the leading predisposing factor to frost cankers regardless of species. Studies done by Dr. Robert Miller, Professor of Urban Forestry at the University of Wisconsin-Stevens Point, suggest that with frost cracks, internal defects were present and common causes were trunk injuries, broken or torn branches and flush pruning wounds, all of which had been covered over with new wood. Over the years, these old wounds become buried under new wood but the original wound area remains weak so that as the tree warms by day and cools by night, physical stresses start the process of splitting the wood from weak areas at the original injury towards the surface. Slowly the crack works its way to the surface until finally on a cold night the tree splits open.

What can be done to prevent frost cracks? They can be prevented by avoiding trunk injuries and by proper pruning.

In other words, avoid wounding trees when they are young. Be particularly careful not to injure the stem with mowers or trimmers. Mulch around young trees and be sure to give them plenty of water. Though generally only cosmetic and not harmful to the tree, Frost Crack is a tell tale sign that we should be diligent about not allowing that tree to become stressed.

The Pros and Cons of Tree Wrapping - One thing stands out above all other advice when choosing to wrap your trees to prevent Sunscald/Frost Cracking......the wrap must be removed before spring or you could be setting your tree up for a plethora of problems including creating a moist haven for insects, fungi and bacteria. Since even the trunk of a tree is part of the photosynthesis process, which occurs even during dormancy, wrapping could interfere with this process especially in young trees.

So what may sound like cannon fire in your backyard in the middle of a cold winter night, is probably your tree telling you something and if we want our trees to live a long and healthy life, it would certainly pay to listen.

---