Q. Our Kwanzan cherry (Prunus serrulata) tree's trunk is splitting. It seems to me it has grown so fast that its "skin" burst. We do not want to lose this tree. Any help you can give us will be much appreciated.

The writer included photos that clearly show a significant crack in the bark that runs from the ground to the crotch of the tree.

A. There are a number of reasons that trees develop cracks in their trunks and branches. Certain species of trees seem most susceptible, including Kwanzan ornamental cherries, many maples and fruit trees. However, it can happen any thin-barked tree, especially when they are young or newly planted.

Fortunately, these cracks are not usually life-threatening for the tree. Otherwise healthy, vigorous trees generally form callus tissue over the wound and live for many years with no problem.

Cracks in the trunk can become a structural issue for trees that are expected to grow fairly large, such as some species of maple. That crack is a weak point where the tree can break during windstorms or heavy snow or ice loads. Structural weakness is not as much of an issue with a small ornamental or fruit tree. Cracks may provide an entrance for pathogens that can cause eventual decline of affected trees.

Environmental conditions at different times of the year contribute to the development of cracks in tree trunks and limbs. In late winter and early spring, rapid thawing of tissue after a bitter cold night can lead to frost cracks, especially on the south or southwest side of the trunk or branch that receives the most intense sunlight. Research has shown that these cracks often develop where the tree was damaged earlier in its development. Such damage is often not visible initially because it is contained in the inner wood of the tree. It only becomes evident when frost causes that crack to expand and split the bark.

A related winter injury is known as sunscald. This occurs when the south or southwest sun warms the cambium (the thin layer of actively dividing cells that gives rise to the tree's vascular system) enough to break dormancy, then refreezes when the sun sets. The most common symptom is that the bark in the damaged area peels away during the growing season following the injury, leaving a sunken area. Callus tissue forms around the edges of the wound as the tree attempts to heal the damage. Cracks can develop at the site of sunscald damage.

Inconsistent conditions during the growing season can also be responsible. Dry weather followed by a period of heavy rain can force excessive growth that is in line with your observation that the tree seemed to grow so fast that its bark split. The erratic growing conditions we have had in 2011 reinforces that observation: excessive rain in spring that forced a lot of lush growth, followed by hot, dry weather, followed by more intense rainfall. Plants do not know if they are coming or going!

There are some things you can do to help your Kwanzan cherry tree recover and thrive, including:

• Avoid using pruning paint, tar or anything else as a wound dressing. Healthy, vigorous trees are perfectly capable of forming callus tissue to heal over such wounds on their own. Research shows that wound paints interfere with this process.

• Avoid heavy pruning or high nitrogen fertilizer after early July to avoid pushing new growth that will not harden off in time for winter.

• If you wish to thin trees with dense crowns, it should be done over a period of years rather than all at once. Suddenly exposing the tree's trunk to intense sunlight after it has always been shaded has about the same affect on the tree's bark as you lying in the tropical sun in January without the benefit of sunscreen.

• Minimize sunscald and frost cracks on young trees by wrapping their trunks with tree wrap or reflective white plastic tree guards to protect them from winter sun. Be sure to remove the wrap in spring so that insect and disease problems do not get started out of easy view and to avoid girdling the tree as it grows in diameter. This should be done for the first two or three years or until the tree begins to develop more mature, thicker bark.

• Have the soil around the tree tested and fertilize in spring according to the recommendations to promote tree vigor.•

• Provide supplemental water during hot, dry weather. An inch of water a week within about 18 inches of the trunk will help protect it from drought stress. You can use a soaker hose or remove the nozzle from a standard hose and allow it to trickle slowly around the base of the tree. Be sure to move the hose periodically so the tree is adequately watered around the entire circumference of the trunk.

• In Allegheny County, Penn State soil test kits for home gardeners cost $12 each and come with detailed instructions for taking a good soil sample and information to help you understand your soil test results. Customers ordering multiple kits at one time pay $9 each for the additional kits. Send a check made payable to Penn State Extension to 400 N. Lexington St., Pittsburgh PA 15208. Write Attn. Soil Test Kit in the lower left corner of the envelope.

First Published: October 8, 2011, 4:00 a.m.