When winter splits the wood: Understanding frost cracks in trees

On a bitter winter morning, a sharp, rifle-like crack may echo through a quiet park or woodland. Startled walkers sometimes imagine a falling branch or distant gunshot. In many cases, the sound comes from a tree itself. Known as frost cracking, this dramatic phenomenon is a common but often misunderstood effect of extreme cold on trees. Frost cracks are long, vertical splits that appear in the trunks of trees, most often during winter. They form when temperatures drop rapidly, especially after a sunny day followed by a freezing night. During daylight hours, the sun warms the outer layers of a tree's trunk. When night falls and temperatures plunge, those outer layers cool and contract much faster than the inner wood. The resulting stress can cause the trunk to split with an audible bang. Not all trees are equally vulnerable. Frost cracking is most common in species such as maples, walnuts, apples, cherries, lindens, dogwoods, and sycamore. Young trees with thin bark and older trees with existing weaknesses are particularly at risk. South and southwest-facing sides of trunks, which receive the most winter sun, are also more prone to cracking. Visually, a frost crack appears as a narrow, vertical opening that can run several feet up the trunk and in some cases the branches. In severe cases, the split may penetrate deep into the wood. While the sight can be alarming, frost cracks are generally not fatal. Trees have a remarkable ability to heal. Over time, new layers of wood may grow over the damaged area, forming a raised ridge known as a "frost rib." However, frost cracks can create long-term problems. The open split allows moisture, fungi, and insects to enter the tree. Repeated freezing and thawing can cause the crack to reopen year after year, gradually weakening the structural integrity of the tree resulting is increased susceptibility to breakage and decay. Preventing frost cracks entirely is difficult, but there are steps that can reduce the risk, particularly for young or newly planted trees. Wrapping trunks with tree guards or light-colored materials can help reflect sunlight and moderate temperature changes. Planting trees in locations to reduce sun load exposure during the winter months. Prevent wounding the tree trunk by following proper pruning and mowing practices. Ensure there is good soil hydration especially during fall and during periods of extended draught conditions. It is important not to overreact if frost cracks do occur. Frost cracks should not be filled with sealants or paint, as this can trap moisture and worsen decay. Instead, damaged trees should be monitored over time. Consulting a certified arborist is advisable if a crack appears large, recurrent, or accompanied by other signs of decline. As winter extremes become more unpredictable, frost cracking may become more common. The sudden sound of a tree splitting in the cold is a reminder that trees, though sturdy and silent most of the year, are living organisms responding to the stresses of their environment. Understanding frost cracks helps us appreciate both the vulnerability and resilience of the trees that line our streets and landscapes. For additional information on frost cracking, you can refer to the following links: https://www.canr.msu.edu/news/frost_cracks_in_trees https://trees.umn.edu/sites/trees.umn.edu/files/2021-10/frost_cracks_and_cankers_faq_sheet.pdf https://homegarden.cahnr.uconn.edu/factsheets/frost-cracks-and-sunscald-on-trees/ https://bygl.osu.edu/node/2465