What Is Frost Cracking, and How Can You Prevent It in Your Trees?
One of the most common problems for trees in winter is frost cracking—when rapid temperature changes cause the outer layer of tree trunks to break. Sometimes, the impact is minimal, but large damage can result in long-term consequences for a tree. In this article, we’ll go over why frost cracking happens, as well as some tips on what you can do to protect your trees when they’re most vulnerable.
What Are Frost Cracks in Trees?
Frost cracks occur when air temperatures fluctuate below and above freezing or when sunlight warms a tree up in the daytime before the tree refreezes at night. When the moisture in the outer layers of a tree melts and then quickly refreezes, the rapid expansion of the ice breaks the outer layer of wood and bark, resulting in a (usually vertical) split. Bark is a tree’s natural protection, and broken outer bark exposes the sensitive inner layer of fresh, actively growing wood.
Frost cracking generally affects the trunk of a tree, particularly in the lower to middle sections where much of the tree’s moisture is stored. A frost crack can be anywhere between a couple of inches to several feet, depending on the size and type of tree. Some of the factors that affect a tree’s vulnerability to frost cracking include the type of bark a tree has, the species of tree, and its age.
Trees with thin bark, such as maple, birch, black cherry, elm, and sycamore, are more susceptible to the thaw-and-freeze cycle. Trees with particularly thick, textured bark, like oak, chestnut, and many evergreen trees, are more tolerant of temperature fluctuations.
Young trees of all species are more at risk of cracking in temperature fluctuations than mature trees due to their thin, smooth bark, small trunk size, high moisture content, and lack of root establishment.
How Do Frost Cracks Damage Trees?
A frost crack breaks the underside of the bark, which is responsible for new growth and healing. The wider the split, the more open the gap, and the more the tree’s inner wood is exposed to the elements. This can cause damage down the line, as this opening makes the tree vulnerable to fungal and bacterial infections or pests.
A particularly deep frost crack may also disrupt moisture and nutrient transport, potentially leading to long-term weakness. However, frost cracks don’t usually kill a mature, healthy tree. Trees can callus over the damaged area of a small crack and form scar tissue, while larger damage may be able to be treated by a certified arborist.
How to Protect Trees From Frost Cracking
In urban areas, where trees get a lot of sunlight exposure and where the urban environment radiates heat, temperature fluctuations are particularly common in late fall and early spring. There are several ways that residents can take preventative measures to reduce the likelihood of frost cracking throughout the colder months of the year, including:
Wrap the trunk: Use commercial tree wraps, burlap, or even light-colored plastic tree guards to protect the trunk during winter. This insulation helps regulate temperature changes and prevents rapid expansion and contraction of the bark.
Maintain consistent watering: Ensure trees are well-watered in the fall before the ground freezes. Adequately hydrated trees are less likely to suffer from frost cracking, as moisture helps regulate their internal temperature.
Mulch: Apply a layer of mulch (two to four inches) around the base of the tree, extending out to the drip line. Mulch helps retain soil moisture and temperature, reducing the effects of sudden temperature changes.
Choose native or cold-hardy species: Selecting tree species that are well-suited to your climate will minimize the risk of frost cracking. Trees adapted to Nashville's climate are less likely to be affected by temperature changes.
Avoid late-season pruning: Refrain from pruning trees in the fall, as this can stimulate new growth that is more vulnerable to winter damage. Prune in late winter or early spring instead, when the tree is still dormant.
Protect Your Nashville Trees in Winter
Even though cold temperatures can put young trees at risk, fall and winter are the best times to plant a new tree! Just be sure to wrap it up for winter over the first several years, after which time the tree’s bark becomes more robust. If the tree has south-facing exposure, consider wrapping it for a few more years since the sun shines from a southern angle during the winter.
Browse the Nashville Tree Conservation Corps’ tree sale for a range of cold-hardy tree species! You can also volunteer with us and help plant and care for trees across the city. If you’re limited on space and time, consider donating a tree for us to plant or making a financial contribution to NTCC to help fund our mission. As a non-profit, we rely on the helping hands of Nashvillians in a variety of ways to support our local canopy!
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