Frost Cracks FAQ

Questions:


»A couple of years ago a large basswood tree on our property got a crack in it. It is about 20 feet long starting about 3 feet off the ground. It happened about this time of the year. We left it alone and figured in the spring the tree would be dead. It did not die, but seemed to be healed over. Now again this year the crack reappeared. Is there anything we should do for the tree or just wait till spring again and see if it lives through the winter again? The tree is fairly close to our house.

»How do I treat a split bark in a Maple tree? Split is accuring on the south side of the tree. Either frost crack or heat related. Approximately two feet long and spreading. These trees are approximately 14 years old.

Minnesota Master Gardeners say:

 Thin barked trees often develop what we call 'sunscald', a type of winter injury. On sunny winter days, the cambium (thin layer of living tissue just beneath the bark) on the south or southwest side of these trees warms up nicely, much warmer than the air temperature, and this layer expands. When the sun goes down, the temperature of the woody tissue suddenly plummets, and because the outermost tissue cools faster than the inner tissue, a crack happens.

A good website to look at is the Yard and Garden Brief on winter injury to trees:
http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/P466winterinjury.html

I believe it was February that was named "Month of the Popping Trees" by Native Americans, because so many aspen trees experienced sudden cracking, loud enough to be heard, after the sun went down. Your crack never went away, but most likely became more obvious because your tree had a flush of fall growth. The crack will exist as long as the tree does. There isn't much you can do about it at this point, other than give the tree normal good care, in particular making sure it doesn't suffer from drought. If you notice evidence of a fungal infection, though, such as conks or brackets, (light-colored growths on the outside of the tree) then you might consider having the tree removed, before it becomes a hazard.

Prevention is the best way to deal with sunscald. Shade the trunks, with boards tied loosely to the south-southwest side during the winter. Or use the white trunk protectors. (Wrapping is no longer recommended. It doesn't necessarily keep the bark cool.) The key is to keep the tree uniformly cold in the winter.