How to Tell If a Tree Is Rotten Inside

How can you tell if a tree is rotten inside but looks healthy on the outside?

You can often tell by looking for a combination of ground-level signs: a fungal conk or mushroom growing from the trunk or root flare, a hollow or soft spot when you press a screwdriver into the base, a cavity, a vertical seam or crack in the bark, and dead stubs in the crown. Any one of those is a reason to look closer. Two or more together is a reason to treat the tree as suspect.

Internal decay starts where water collects, usually at the root flare, an old wound, or a broken branch stub. The tree keeps producing sound wood on the outside, so the canopy can stay green while the core is hollow. That is why a healthy-looking crown is not proof of a healthy trunk.

• Look at the base first, not the top.
• Fungal growth on the trunk or root flare is the clearest outward clue.
• A cavity, crack, or soft spot is a structural warning.
• Lean, soil heave, or a suddenly thinning crown raises the urgency.

What the signs actually tell you

A conk or mushroom at the base means decay fungi are already working inside the wood. The fruiting body appears when the fungus has enough moisture and food, which usually means the decay has been running for a while. The presence of the conk is more informative than its size.

A hollow sound when you tap the trunk with a mallet or the handle of a tool is a soft clue, not a diagnosis. Sound wood rings; decayed wood thuds. The catch is that a hollow tree can also sound dull for other reasons, and a tree with a small pocket of decay can still sound solid. Use the tap as one data point, not the answer.

A cavity you can see is a hole where decay has already broken through. The size of the opening matters less than what is behind it. A narrow slit can hide a wide hollow. A wide opening with sound, callused edges can be less serious than a small hole weeping dark liquid.

Bark seams and vertical cracks are the trunk telling you it is splitting under load. When you see a seam running up from the root flare, the tree is carrying its weight on less wood than it appears to have.

A self-check you can do from the ground

Stand back and look at the whole tree before you walk up to it. Most of what you need to see is visible from a safe distance.

• Is there a conk, mushroom, or shelf fungus on the trunk or at the base?
• Is there a cavity, hole, or dark oozing patch?
• Is there a vertical crack or seam in the bark?
• Does the base of the trunk flare outward normally, or does it look pinched or flattened on one side?
• Is the tree leaning more than it used to, or leaning toward a house, driveway, or power line?
• Is the soil cracked or heaved up on one side of the trunk?
• Are there dead branches in the top that were not there last year?
• Did the tree leaf out later than its neighbors, or is the crown thinner than theirs?

Do not dig around the root flare or cut into the trunk to check. Wounding the tree can start or speed up the decay you are trying to assess.

Why a green canopy can hide a hollow trunk

A tree can hold a full, green canopy while most of its interior wood is gone because the living part of the trunk is a thin shell just under the bark. The outer layers carry water and nutrients; the inner wood is mostly structural. Decay fungi eat the inner wood first, so the tree keeps photosynthesizing and looking normal while its strength drops.

This is why a tree that looks fine in July can fail in a windstorm in September. The canopy is not the load-bearing part. The trunk and root flare are. When those are compromised, the tree can stand for years and then come down without much warning.

Some species compartmentalize decay better than others, walling it off and living for decades with a hollow. Others rot faster and lose strength sooner. We cannot tell you which without looking at the tree, but the pattern is the same: outward health and internal soundness are two different things.

When to stop guessing and get the tree looked at

Get the tree assessed when you find a conk at the base, a cavity, a vertical seam, or a lean toward something you care about. Those are the signs that move a tree from 'watch it' to 'have someone look at it.'

A leaning tree with a fungal conk at the base is the combination that concerns us most. The lean means the root plate or trunk is already moving; the conk means the wood holding it is decaying. A tree like that over a house, a driveway, or a power line is a candidate for removal, not pruning.

Call us at (910) 555-0123 to describe what you see. We will ask about the lean, the fungus, the cavity, and what is underneath the tree. That conversation tells us whether the tree needs an on-site look and whether removal is the right call.

What a removal assessment involves

An on-site assessment means we walk the tree, look at the root flare, check for cavities and conks, and look at what the tree would hit if it failed. We are not diagnosing with a resistograph or a sonic tomograph unless the situation calls for it; most of the time the visible signs plus the target underneath tell us what we need to know.

What drives the cost of removal is not the height alone. It is the lean, the decay, the proximity to structures and lines, the space we have to work in, and whether the tree can be dropped in one piece or has to come down in sections. A hollow tree near a house is a different job from a solid tree in an open field, even if they are the same size.

We will tell you what we see and what the options are. If the tree can be pruned and monitored, we will say so. If it needs to come down, we will explain how and why.

What to ask before anyone touches the tree

Ask what the plan is for the wood, the stump, and the cleanup. Ask how the tree will be taken down if it cannot be dropped whole. Ask what happens to the lawn, the fence, or the driveway during the work. Those answers tell you more about the job than a price alone.

Ask whether the tree can be climbed or has to be worked from a bucket, and whether any part of it overhangs a structure. A hollow tree changes how a climber can safely tie in and where weight can be placed. If the tree is rotten, the rigging plan has to account for wood that may not hold a spike or a notch the way sound wood does.

Ask what the crew will do if the tree shifts while it is being worked. A plan for a leaning, decayed tree includes a way to stop and reassess, not just a cut list.

The decision, in one pass

If you see a conk, a cavity, a seam, or a lean toward something you value, treat the tree as a removal candidate until someone looks at it. If you see none of those and the crown is full and the base is sound, keep an eye on it and check again after storm season.

Do not wait for the tree to drop a limb before you act. A hollow tree that has stood for years can still fail in the next wind event, and the signs are usually visible before the failure. Look at the base, take a photo, and call us at (910) 555-0123 if what you see worries you. We serve Fayetteville, NC and the surrounding area, and we will tell you what we see when we get there.