My friend Julie asked why the trunk on her maple tree was splitting vertically. I have a pine oak with a splitting trunk. Why? According to Cornell University, bark splitting can occur at various times of year and for a variety of environmental reasons. While splits are more common on the trunk of a tree, branches may also be affected. Bark splitting is not usually fatal, although the open wound can allow the entry of decay-causing disease organisms. Sometimes splitting is a way for the tree to open outer layers of dead bark, which cannot grow. The crack then allows the tree to grow in diameter. Or sometimes the tree is growing so quickly it forms a vertical crack. Splitting in winter or early spring is often referred to as a frost crack. Late rapid fall growth due to warm temperatures, high humidity and high levels of nitrogen may make trees more prone to frost cracking during winter, particularly on the south or west sides of the trunk. To discourage this, don’t fertilize trees late in the growing season, unless you fertilize after leaf drop and dormancy. Thin-barked trees, such as maples and fruit trees can experience sunscald in the winter because they have no leaves to shade their trunks. The damage may not show up until the summer. Light-colored tree wraps can be applied in the fall to reduce sunscald. They need to be removed after the cold weather has passed the following spring. Also, in spring and summer, dry weather that slows growth followed by wet weather or better growing conditions can encourage a large spurt of vigorous growth, which can initiate growth cracks. I think Julie’s tree may have gone through a dry spell followed by her increasing the water. Now the tree wants to grow. Occasionally, a circling root at the base of the trunk squeezes the trunk preventing moisture and nutrients from moving up and down the tree properly. The constriction ends up splitting the trunk. My oak may have a circling root. Do not put tree wound paints or tar over cracks. These products do not help a tree to callus over a wound. Keep your tree healthy and vigorous so it can compartmentalize and callus over the wound on its own. To help a tree do this, fertilize each spring and give it enough water on a regular basis, including in fall and winter. The Cornell site outlines a procedure for “tracing the bark around the split” to help in wound healing. Tracing bark involves using a sharp, disinfected knife to cut back the ragged bark to create a clean edge to speed callus development. For information on bark splitting trees see the Cornell site at: http://www.plantclinic.cornell.edu/factsheets/barksplitting.pdf JoAnne Skelly is Associate Professor & Extension Educator Emerita at the University of Nevada Cooperative Extension. Reach her at skellyj@unr.edu
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