Cracks, Cavities & Leaning Trunks: What These Tree Warning Signs Actually Mean

Every mature tree has imperfections. A little bark damage from a mower, an old wound that's healed over, a hollow spot that's been there for twenty years and never caused a problem — trees live with all kinds of flaws and keep right on standing. That's actually one of the more remarkable things about them.

So when does a flaw stop being just a flaw and start being a real concern? That's the question we get asked most often when we walk a property — and it's a good one, because the honest answer is: it depends on a handful of specific factors that aren't always obvious from the ground. Here's how to think through it.

Cracks: Location and Direction Matter More Than Length

Not all cracks are created equal. A short, shallow seam in the bark that's been there for years and shows signs of healing (new bark growing in around the edges, called "callus tissue") is usually just cosmetic — the tree has sealed it off and moved on. What changes the picture:

Cavities and Hollows: Old News or Active Problem?

Hollow trees are more common than people think, and a lot of them are perfectly stable — there's actual science behind why. A tree's strength comes mostly from the outer rings of wood (the living, structural layer), not the dead heartwood at the center. A tree can be hollow in the middle and still be structurally sound, the same way a metal pipe doesn't need to be a solid rod to hold weight.

What matters is how much of that outer structural wall remains intact, and whether the cavity is actively growing. As a rough rule of thumb that arborists often use: when the remaining solid wall of wood drops below roughly a third of the trunk's radius, the structural risk increases significantly. You can't measure that precisely from the ground, but you can watch for the signs that point toward "this cavity is a problem" versus "this cavity has been here for decades and isn't going anywhere":

Signs the cavity may be a real concern: the opening is large relative to the trunk's overall diameter, you can see active decay (soft, discolored, crumbling wood) rather than smooth, dry interior surfaces, the cavity is paired with other issues like a lean or cracking nearby, or the tree is in a spot where failure would land on a structure, driveway, or area where people regularly are.

Signs it's likely stable: the cavity has clearly been there a long time (you can see old, weathered wood and healthy bark growth around the edges), the tree shows no other signs of decline, the canopy is full and healthy, and there's nothing nearby that would be impacted if the unlikely happened.

This is genuinely one of the harder calls to make, and it's exactly the kind of judgment that comes from years of looking at trees in person — what looks alarming from the driveway sometimes turns out to be completely stable, and what looks fine from a distance sometimes isn't. If a cavity is bothering you, it's worth having someone take a closer look rather than guessing either direction.

Leaning Trunks: New Lean vs. Old Lean

This is the one we want homeowners to pay closest attention to, because the distinction is genuinely simple even though the underlying cause can be complex.

An old lean is a tree that has grown at an angle its whole life — often reaching for sunlight, growing around an obstacle, or just developing that way from a young age. The trunk has typically thickened and reinforced itself on the side that needs the extra support (you'll sometimes see a slightly flared, reinforced look at the base on the lower side of the lean). These trees can stand that way safely for generations.

A new or progressing lean is different — and it's one of the more urgent signs on this whole list. If a tree that was standing straight (or at a stable angle) is now visibly tilting, or if a long-standing lean appears to be getting more pronounced, that usually means something underneath has changed: root failure, soil saturation and erosion, root rot, or storm damage to the root system. The clearest red flag of all is soil that's lifting, cracking, or mounding on the ground on the side opposite the direction of the lean — that's the root plate beginning to separate from the earth, and it can mean the tree is at risk of toppling. That situation should be treated as urgent, not something to keep an eye on over the next few months.

Putting It Together: When to Call and When to Relax

Here's the most honest summary we can give you: a single issue, on its own, on an otherwise healthy tree, usually isn't an emergency. It's the combination — and the trend over time — that tells the real story.

A tree with one old, healed-over cavity and nothing else going on has probably been fine for years and will probably be fine for years more. A tree with a fresh crack at a branch union, fungal growth at the base, AND a lean that wasn't there last spring is telling you the same thing three different ways, and that's not a "wait and see" situation.

If you're standing in your yard looking up at something that gives you a bad feeling, trust that instinct enough to get it looked at — even if it turns out to be nothing. We'd much rather drive out, take a look, and tell you "that tree's going to outlive both of us" than have you find out the hard way during the next windstorm. That call costs you nothing and it might save you a much bigger headache down the road.