What Is Frost Crack: What To Do For Cracking Tree Trunks

A tree with peeling bark and a long vertical crack
(Image credit: Lokibaho)

During periods of cold winter nights followed by warm sunny days, you may discover frost cracks in trees. They can be several feet (1 m.) long and a few inches (8 cm.) wide, and the colder the temperature, the wider the cracks. Frost cracks usually occur on the south to southwest side of the tree.

What is Frost Crack?

The term “frost crack” describes vertical cracks in trees caused by alternating freezing and thawing temperatures. When the bark alternately contracts with freezing temperatures and expands on warm days, a crack is likely to occur. A tree with a crack is in no immediate danger and may live for several years.

Reasons for Frost Crack in Trees

Frost is just one of the causes of tree bark cracking. You'll also see cracking tree trunks from a condition called sunscald. In late winter or early spring, the warm afternoon sun shining on the trunk can cause the tree tissue to break dormancy. When sunny afternoons are followed by freezing nights, the tissue dies. You may find strips of bark peeling off the tree. Dark-colored and smooth-barked trees are most susceptible to sunscald.

Cracking tree trunks also occur in trees grown in areas where they are marginally hardy. Hardiness zones reflect the lowest expected temperature in an area, but all areas experience unexpectedly low temperatures from time to time, and these low temperatures can damage trees growing on the edges of their hardiness zones.

How to Fix Frost Crack

If you're wondering how to fix a frost crack, the answer is that you don't. Sealants, wound paint, and adhesives have no effect on the healing process or the health of the tree. Keep the crack clean to prevent infection and leave it open. In many cases, the tree will attempt to heal itself by forming a callus along the crack.

Once a crack occurs, it is very likely that another crack will form in the same location. You can help prevent a re-occurrence by wrapping the trunk of the tree in tree wrap for the winter. Remove the wrap as soon as temperatures warm in late winter or spring. Leaving the wrap on too long provides a secure hiding place for insects and disease organisms.

Another way to protect the tree is to plant evergreen shrubs around the trunk. Shrubs can insulate the trunk from extremes in temperatures and shield it from direct afternoon sunlight. You should prune the canopy of surrounding trees conservatively to avoid removing branches that shade the trunk.

Jackie Carroll

Jackie Carroll has written over 500 articles for Gardening Know How on a wide range of topics.