You notice a crack in your tree trunk. Your first instinct is to panic. Is the tree going to fall? Does it need to come down immediately? Or is it just a cosmetic issue that’ll be fine?
The answer is: it depends on the type of crack.
Not all cracks in trees are created equal. Some cracks are serious warning signs that the tree is failing. Others are just the tree’s way of dealing with stress, and they won’t cause problems. Knowing the difference between them can save you thousands in unnecessary removal costs and help you identify real hazards before they become dangerous.
At Rock Creek Tree, Turf & Landscape in Montgomery County, we evaluate cracked trees all the time. Here’s what we look for and what you should know about the cracks in your trees.
The Different Types of Cracks and What They Mean
There are several types of cracks that show up in tree trunks and branches. Each one has a different cause and a different level of concern.
Vertical Cracks (Frost Cracks): Usually Not Dangerous
What they look like: Long, straight cracks running parallel to the length of the trunk. They’re usually pretty obvious and can be several feet long.
What causes them: Vertical cracks, also called frost cracks, happen because of rapid temperature changes. The sun warms the south or southwest side of the tree during the day, which warms the bark and the wood just below it. When the temperature drops sharply at night (which is common in Maryland winters), the bark and outer wood contract faster than the inner wood. The outer layers crack from the stress.
This is especially common in late winter when we get those weird warm days followed by freezing nights.
How to spot them: They’re hard to miss. Long vertical splits, usually on the south or southwest side of the tree. Frost cracks often open and close seasonally. They might be wider in winter and narrower in summer, but they usually come back the same spot year after year.
Is it dangerous? Usually not. A vertical frost crack is mostly cosmetic. The tree compartmentalizes the crack, and the tree doesn’t necessarily fail because of it. However, open cracks are entry points for pests and disease. Over time, if the crack keeps opening and closing and allowing water and pathogens in, the tree can decline.
What to do: If it’s a minor frost crack, you can leave it alone. If it’s severe or if the tree is showing other signs of decline, have it evaluated. In some cases, we can brace or cable the tree to reduce the stress and keep the crack from getting worse. But don’t assume a frost crack means the tree has to come down. Most trees live for decades with frost cracks.
Torsional Cracks: Concerning, but Not Always Fatal
What they look like: Spiral or corkscrew-shaped cracks that wrap around the trunk or branch. They look like the tree got twisted.
What causes them: Torsional cracks happen when the tree gets twisted, usually by strong winds. If the tree has uneven weight in the canopy or weak branch attachments, the twisting stress can cause the wood fibers to shear apart in a spiral pattern.
How to spot them: Look for cracks that spiral around the trunk or run along branches in a twisted pattern. Often you’ll see other signs of stress nearby, like broken or hanging limbs.
Is it dangerous? It depends. A minor torsional crack isn’t necessarily fatal, but it’s a sign that the tree experienced significant stress. The tree can compartmentalize the crack and survive, but it also means the tree’s structural integrity has been compromised. That tree is more vulnerable to failure in future storms.
What to do: If you see a torsional crack, especially if it’s large or if you see multiple cracks, have the tree evaluated. The tree might be structurally sound enough to keep, or it might be a candidate for removal or cabling. Either way, you want professional assessment because this isn’t a crack you can ignore.
Shear Cracks: These Can Be Serious
What they look like: Diagonal or cross-grain cracks, often appearing near the base of the trunk or where large branches meet the trunk.
What causes them: Shear cracks form when the trunk is bent or overloaded unevenly, usually during storms or heavy winds. When the wood is stressed on one side, it splits diagonally. Trees on slopes or uneven ground are also vulnerable to shear cracks because the weight distribution is naturally unbalanced.
How to spot them: Look for diagonal cracks, especially around the base of the tree or at branch junctions. The bark around the crack often shows signs of stress or peeling.
Is it dangerous? Shear cracks are more concerning than vertical frost cracks because they indicate structural weakness. A single shear crack might not be fatal, but it means the tree has been significantly stressed and may be more likely to fail in future storms.
What to do: Have the tree evaluated. A professional can determine whether the crack is superficial or if it’s compromised the tree’s structural integrity. Sometimes the tree can recover with proper care and perhaps some bracing. Other times, the tree needs to come down because it’s too unstable to leave standing.
Horizontal Cracks: Potentially Dangerous
What they look like: Cracks that run perpendicular to (across) the length of the trunk, usually appearing as lines where the bark separates or bulges outward.
What causes them: Horizontal cracks are usually caused by internal pressure building up inside the tree. This can happen from excessive growth, water retention in the wood, or fungal decay. The pressure builds until the wood splits horizontally.
How to spot them: These can be harder to see than vertical cracks because they might be hidden under loose bark. Look for horizontal lines where the bark appears to separate, bulge, or peel away from the trunk.
Is it dangerous? Horizontal cracks are more serious than vertical ones. They weaken the tree’s structural integrity significantly because they run perpendicular to the grain of the wood. A tree with a major horizontal crack is at risk of splitting or breaking, especially in storms.
What to do: If you see a horizontal crack, especially a large one, call a professional immediately. This is not a crack you want to ignore. The tree may need to be removed for safety reasons.
Radial Cracks: Check for Decay
What they look like: Cracks that extend outward from the center of the trunk or branch, like spokes on a wheel. Often there are multiple cracks radiating from one central point.
What causes them: Radial cracks are typically caused by internal decay or fungal infection that compromises the core of the tree. As the tree weakens from decay, the outer wood cracks outward.
How to spot them: Look for cracks radiating from a central point. Often you’ll also notice soft or spongy wood, or you might see fungal growth (mushrooms, shelf fungi) near the crack.
Is it dangerous? Very. Radial cracks indicate serious internal decay, which means the tree’s structural integrity is compromised. A tree with radial cracks is at high risk of failure.
What to do: Have the tree removed. Radial cracks almost always mean the tree is too far gone to save. The decay is extensive, the tree is unstable, and it poses a serious hazard.
How to Assess a Crack: The Questions to Ask
If you find a crack in your tree, ask yourself these questions:
How wide is it? A hairline crack is less concerning than one you can stick your finger into. Wide cracks indicate more severe stress.
How long is it? A small crack is less serious than one that runs several feet along the trunk.
Where is it? Cracks at the base of the tree or near branch junctions are more concerning because these areas bear more weight and stress. A crack on the upper trunk is less critical.
Are there other cracks? One crack might be manageable. Multiple cracks scattered around the tree suggest systemic stress and structural compromise.
Is there evidence of decay, pests, or disease? If you see soft wood, fungal growth, or pest damage around the crack, the tree’s health is compromised beyond just the crack itself.
Is the tree leaning? If the tree has a crack AND is leaning, that’s a bad combination. The lean plus the crack suggests the tree is unstable.
How is the rest of the tree? Is the canopy full and healthy, or is the tree showing other signs of decline (dead branches, thinning canopy, discolored leaves)? A tree with a crack that’s otherwise healthy is more likely to survive than a tree with a crack that’s also declining.
When to Panic, When to Wait, and When to Call a Pro
Panic (Call immediately):
- Large horizontal cracks
- Radial cracks with evidence of decay
- Shear cracks on large trees
- Any crack on a tree that’s close to your house, driveway, or other structure
- Multiple cracks on the same tree
- Cracks accompanied by other signs of serious decline
Wait and monitor (But get it evaluated):
- Small vertical frost cracks on otherwise healthy trees
- Minor torsional cracks without other signs of stress
- Small, single cracks with no evidence of decay
Definitely call a professional:
- If you have any doubt about how serious the crack is
- If the tree is large or close to structures
- If the crack is more than just surface-level
- If you see fungi, decay, or other signs of disease around the crack
The Bottom Line
Not every crack in a tree is a death sentence. Vertical frost cracks are common and often cosmetic. But horizontal cracks, radial cracks, and multiple shear cracks are serious and need professional assessment.
When in doubt, have the tree evaluated. A professional can look at the crack, assess the tree’s overall health and structural integrity, and tell you whether the tree is safe to keep or if it needs to come down. It’s cheap insurance against a tree failing unexpectedly.
At Rock Creek Tree, we’ve seen every type of crack there is. We can tell you whether your tree is going to be fine or whether it’s time to plan for removal. If you’ve noticed cracks in your trees and you’re not sure whether they’re a concern, call Rock Creek Tree, Turf & Landscape at 301-580-6023 or contact us for an evaluation. We’ll take a look, give you an honest assessment, and help you figure out the best next step.
