Cracks and splits in tree trunks are fairly common and may occur for various reasons.
They are usually not a significant threat to the tree. Typically there's not much you can do about
them once they occur.
One of the most common reasons for cracks and splits on tree trunks is cold temperature.
These are called frost cracks and are caused when the inner and outer wood in the tree's trunk
expands and contracts at different rates when temperatures change. This happens when winter
temperatures plummet below zero especially after a sunny day when a tree's trunk has been
warmed by the sun. The different expansion rates between the inner and outer wood can cause
such a strain on the trunk that a crack develops. Frost cracks occur suddenly, can be several feet
long and are often accompanied by a loud rifle shot sound. They often originate at a point where
the trunk has been physically injured in the past. Maples and sycamores are the most prone to
frost cracks. Apples, ornamental crabapple, ash, beech, horse chestnut and tulip tree are also
susceptible. Isolated trees and trees growing on poorly drained soils are particularly prone to
Frost cracks often close during summer only to reopen in succeeding winters. They do
not seriously hurt trees although they provide openings where certain disease organisms may
enter, particularly if the tree is in a weakened condition. Frost cracks are also ideal hiding places
for insects like earwigs, although the insects do not harm the tree directly.
Frost cracks are not preventable. Wrapping the trunks of newly planted trees with tree
wrap paper in the fall may help. If you do wrap, be sure and remove it each spring so as not to
provide homes for insects. Apple growers whitewash the trunks of apple trees to prevent frost
cracks and other winter injury problems. Homeowners can use white latex paint, but some
gardeners may find this unattractive in a landscape setting. The best way to prevent a secondary
effect due to frost cracks is to promote good growth and prevent injury to the trunk throughout
the tree's life.
If damage occurs, simply remove any loose bark hanging along the edges of the crack
using a sharp knife to give a clean cut. There is no need to paint the wound with tree paint. For
large, serious cracks a professional arborists can bolt the cracks shut with a technique called lip
Sun scald is another form of injury that can result in cracks and splits. It occurs in the
winter usually on the south or west side of the trunks and branches. The damage takes place
when the cells in the living tissue beneath the bark break dormancy on warm, sunny days and
then rupture and die when night temperatures drop below freezing at night. The tree is injured
when enough cells in a given area are killed. The following spring these dead areas will appear
discolored and sunken. In time the bark killed by sun- scald will split and peel. These areas also
provide entry points for insects and diseases.
Young thin bark trees are most susceptible to sun scald injury. These include beech,
honey locust, lindens, mountain ash and sugar maples. Heavy pruning on neglected trees can
also expose sections of bark that were previously protected from the sun's direct rays. This can
predispose these areas to sun scald injury. To reduce or eliminate sun scald injury, wrap the
trunks of susceptible trees each fall with tree wrap paper. Do this for one or two seasons until the
bark begins to roughen. Remove each spring so as not to provide a home for insects. Tree
trunks can also be treated with white latex paint.