What Is Frost Crack: What To Do For Cracking Tree Trunks

What Is Frost Crack: What To Do For Cracking Tree Trunks

By: Jackie Carroll

During periods of cold winter nights followed by warm sunny days, you may discover frost cracks in trees. They can be several feet (1 m.) long and a few inches (7.5 cm.) wide, and the colder the temperature, the wider the cracks. Frost cracks usually occur on the south to southwest side of the tree.

What is Frost Crack?

The term “frost crack” describes vertical cracks in trees caused by alternating freezing and thawing temperatures. When the bark alternately contracts with freezing temperatures and expands on warm days, a crack is likely to occur. A tree with a crack is in no immediate danger and may live for several years.

Reasons for Frost Crack in Trees

Frost is just one of the causes of tree bark cracking. You’ll also see cracking tree trunks from a condition called sunscald. In late winter or early spring, warm afternoon sun shining on the trunk can cause the tree tissue to break dormancy. When sunny afternoons are followed by freezing nights, the tissue dies. You may find strips of bark peeling off the tree. Dark-colored and smooth-barked trees are most susceptible to sunscald.

Cracking tree trunks also occur in trees grown in areas where they are marginally hardy. Hardiness zones reflect the lowest expected temperature in an area, but all areas experience unexpectedly low temperatures from time to time, and these low temperatures can damage trees growing on the edges of their hardiness zones.

How to Fix Frost Crack

If you’re wondering how to fix a frost crack, the answer is that you don’t. Sealants, wound paint, and adhesives have no effect on the healing process or the health of the tree. Keep the crack clean to prevent infection and leave it open. In many cases, the tree will attempt to heal itself by forming a callus along the crack.

Once a crack occurs, it is very likely that another crack will form in the same location. You can help prevent a re-occurrence by wrapping the trunk of the tree in tree wrap for the winter. Remove the wrap as soon as temperatures warm in late winter or spring. Leaving the wrap on too long provides a secure hiding place for insects and disease organisms.

Another way to protect the tree is to plant evergreen shrubs around the trunk. Shrubs can insulate the trunk from extremes in temperatures and shield it from direct afternoon sunlight. You should prune the canopy of surrounding trees conservatively to avoid removing branches that shade the trunk.

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What is sunscald?

To answer this question, let’s quickly talk about the layers of tree bark. The outermost layer is appropriately named the outer bark. Directly underneath that is the phloem or inner bark, which funnels food throughout the tree. Then there’s the cambium layer, the growing part of the tree that creates new wood each year.

OK, now sunscald. Here’s how it happens: cells in the phloem and cambium layer that had been dormant (i.e., resting) get activated when sunlight shines on tree bark during a warm winter day. But when the temperature drastically drops at night, those cells are injured. The result is a discolored, sometimes sunken area of bark on the southwest side of the tree.

Will sunscald kill a tree?

Usually, sunscald on trees isn’t fatal. But it depends. Very young trees that don’t have fully developed bark could be damaged to the point that removal is necessary. For mature trees, it’s much less likely that sunscald will be life-threatening.

What causes frost cracks in trees?

Fluctuating winter temps can also cause frost cracks. A repeated switch from warm to freezing temperatures causes the inner layers of bark to expand then shrink over and over. Eventually, that tension causes a crack.

Will frost cracks kill a tree?

Frost cracks themselves likely won’t kill a tree, but they do invite other stressors like insects and disease. That’s why it’s important to spot and identify bark issues early. If you’re not sure if your tree is suffering from sunscald or frost cracks, contact a local office for a consultation.

How to repair split bark on trees

Trees have the incredible ability to seal their own wounds. Through a process called compartmentalization, trees gradually cover wounds with plant tissue and then produce new, healthy wood over the once-damaged area. Cool, huh?

The best thing you can do is leave your tree be during this natural process. But if you’re determined to help, we recommend taking a proactive approach by fertilizing in spring to support new growth.

Preventative winter tree care tips for sunscald and frost cracks

Before winter, take these few steps to protect your trees from injury:

  1. Deepwater your tree all the way up until the ground freezes. Hydrated trees are much less vulnerable to sunscald than drought-stressed trees.
  2. Mulch trees in fall to seal in moisture from tree watering.
  3. Cover the trunk with a tree guard in fall to protect the bark from direct sunlight. Remember to remove the tree guard at the right time.
  4. Consider planting shrubs or smaller plants on the southwest side of the tree to shade its bark.

Throughout winter, keep in mind that symptoms of sunscald may not appear until the season’s over.

Here are signs of winter damage you should look out for in spring.

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Pro-Cut Tree Service

Most trees are resilient enough to withstand natural elements, including harsh winters. Nevertheless, some trees may experience signs of wear or injury. One common problem during the cold season is frost cracks. Learn what these are and how to recognize them.

What Are Frost Cracks?

Despite its name, a frost crack isn’t actually due to frost. It’s due to exposure to sudden temperature fluctuations. In this sense, winter frost plays a role, though it’s not the sole cause.

Frost cracks are common during cold sunny days. The afternoon sun causes the bark, and the wood underneath it, to expand. When the temperature drops at night, the bark cools and shrinks back down faster than the wood. This causes a vertical crack as the bark splits over the wood that remains expanded.

Implications of Frost Cracks

Frost cracks are rarely detrimental. In most cases, the tree self-heals by forming a scab over the crack. However, larger cracks may expose an opening for boring insects and fungus. While emergency tree service is usually not necessary, homeowners should err on the side of caution and enlist a tree care specialist. An arborist can determine whether remediation is necessary.

How to Treat Frost Cracks

As mentioned, frost cracks often cause a vertical split. If the adjacent bark is still firmly attached to the wood, then the tree will heal on its own. Remove loose bark because it will get in the way of the soon-to-form scab. You can also minimize frost cracks by planting shrubs around the trunk. The shrubs provide protection against the sunlight, which is responsible for one-half of the temperature extreme.

We Treat Frost Cracks

Tree care and removal are common during the winter months. Call Pro-Cut Tree Service if you notice any disruptions in the surface bark. Depending on the severity, the frost crack might require human intervention.

Trees with frost cracks in them are often found in open areas. Found on winter days, the inner bark becomes warm by the sunlight. As the temperature drops, the bark begins shrinking.

The wood inside the tree’s trunk slowly contracts as the bark shrinks. This process causes the bark of the tree trunk to split in half — this is a frost crack.

According to the University of Michigan, scientists believe frost cracks are caused by the water moving out cells and freezing within the tree. The wood closest to the tree’s surface shrinks as it loses water.

This is common with younger trees that have thin bark.

Developed trees may suffer from frost cracks. The inside of trees reaches higher temperatures than the air around them.

A few species that are more likely to develop frost cracks include, but are not limited to:

  • Apple trees
  • Beech trees
  • Elm
  • London plane
  • Maple

Tree Scald

Some nights, the air becomes cooler, the temperature drops. As a result, the cambium layer and bark become damaged. This damage isn’t called frost cracks. It’s called tree scald.

Frost Cracks

Susceptible Plants
Deciduous trees, especially young trees with thin bark planted in sunny, exposed sites.

Description & Symptoms
Vertical cracks appear in the winter in the bark of the sunny side of trees, particularly on the side of the trunk oriented to the south or southwest. Frost cracks are injuries caused by the expansion and contraction of bark and underlying tissues in response to warm daytime temperatures and cold nighttime temperatures.

Timing & Life Cycle
Frost cracks are a winter problem that is especially severe if warm afternoon sun is followed by a rapid drop in temperature at sundown. Reflected light from snow cover can exacerbate the problem.

Treatment & Solutions
Select trees that are winter hardy in your region. Siting trees properly is also important. For example, woodland trees that prefer shade may be more prone to frost cracking if planted in a sunny location. Providing water during dry periods, particularly in the fall, will help trees resist cracking during winter stressed trees are more susceptible to frost cracks. Repair is generally not recommended as healthy trees will seal off a wounded area by forming callus tissue around it. Young trees with thin bark should be routinely inspected. Frost cracks are rarely life threatening however, the wounds can present an entry for insects and disease. Recent studies indicate that wrapping tree trunks is not an effective technique for avoiding frost cracks.

Please contact Plant Information Service at (847) 835-0972 or via e-mail at for more information about frost cracking.


I've been fairly disturbed recently to notice some cracks in the bark of a maple and some redbuds in my garden.

Here's the red maple (Acer rubrum) showing cracked bark and some new growth emerging from the trunk below the crack. This tree is probably about 15-20 feet tall, with a bare trunk for 5-6 feet off the ground. When we had a landscaper install it a few years ago, it was already pretty much this height with a very slender, upright growth habit. In other words, the 'canopy' (such as it is) offers little-to-no shade protection for the trunk in a full-sun setting.

This redbud - also in full sun - has a vertical crack extending for several feet along its trunk almost to the soil line.

Yet another full sun redbud (Cercis canadensis) with a crack extending almost the entire length of the trunk. I don't know whether these cracks will kill or hurt the trees - whether they are a symptom of poor health or whether they might cause the trees' demise by providing entry for diseases and insects. Or perhaps the trees will be able to heal themselves and seal the cracks on their own with new bark? I do suspect that sun scald might be part of the problem, so if the trees do survive, I plan on wrapping the trunks with some sort of protective tree paper next winter to protect the bark.

Here's a volunteer redbud looking extremely healthy. It seems to me this little guy has a much bushier growth habit than the redbuds we had installed from a tree nursery. As I understand it (and from what I observe), redbuds often grow naturally in a forest understory or on the edge of a woodland. In those situations, perhaps redbuds would have a lanky, upright growth habit. But it seems to me that in the open, redbuds - like this volunteer - would have a bushier growth habit so that that the leaves could protect the bark of the trunk, at least during the summertime. (This theory sort of falls apart for wintertime protection, since the tree will be bare and the bark probably unprotected regardless of the growth habit of the branches. )

Have you experienced bark cracks due to sunscald or other causes (such as frost crack) on maples, redbuds or other trees? Were you able to protect your trees from such issues with tree wrap or other methods?


Lost a very expensive live oak to Sun scald about 5 years ago. Colder than typical winter got my tree and two others planted by the same landscaper at a different home. Oak struggled for a year sending out new growth below and away from the crack, but to no avail. Replaced with a native red maple and a Trident maple. I have tree wrap in my arsenal, but our winters the last few years have not been as extreme. (Virginia zone 7b). Hoping your trees manage to hang on.

Sorry to hear about your live oak loss. Hope the replacement maples have performed well in your garden.

Interestingly, all of these trees were in fact planted by a landscaper, whereas I have not encountered this problem on any of the trees or shrubs that I planted myself.

Perhaps part of the issue is the fact that the landscaper planted tall trees with narrow canopies where the leaves cannot shade the trunk? In addition, I suspect that tall-narrow growth pattern comes from a nursery that grew the trees close together in rows out in the field where one tree was shaded and protected by lots of neighbors. When the trees were dug and transplanted (because these were all balled and burlapped) and placed in an open, sunny situation, suddenly their trunks were exposed in a way they had not been before and the trees have struggled to cope with the sudden change.

Another interesting point is that the cracks occurred after a relatively mild winter. The trees have been in the ground a few years, but I don't recall seeing any major cracks after harsher winters in previous years

Finally, it could also have something to do with my soil (heavy clay) and the interaction between that soil and the balled-and-burlapped root ball. (I'm not a fan of the B&B method. I think the tree has problems growing out of that root ball and that it's very difficult to get enough roots to support a large tree. I think one usually gets much better results with container-grown plants -- though of course that means starting with a much smaller tree. Still, I think younger container-grown plants often have faster growth rates than the B&B trees, so they can catch up (or close to it) in a few years to their older, taller B&B counterparts. Just my 3 cents.

Watch the video: Landscape Lesson Sunscald Frost Crack