7 Warning Signs a Tree Might Fall in Your Yard

You walk past the same maple every morning, and one day something looks off. The lean is steeper than you remember. There is a soft patch of mushrooms at the base that was not there last spring. You picture the next windstorm and start Googling signs a tree might fall. That instinct is correct. Trees almost never come down without sending warnings first. The hard part is reading them in the right order. A 30-degree lean on a healthy tree is one thing. A 5-degree lean that appeared overnight after a soaking rain is a different problem entirely.

This is the working-arborist version, ordered the way we walk a property on a hazard tree call. We use the ISA framework: risk is the target underneath, the defect in the tree, and the likely failure if it goes. The seven signs below cover the defect side. The two factors at the end tell you whether what you spotted is call-us-this-week or watch-it-through-summer.

1. A cavity or hollow trunk that takes up more than a third of the cross-section

What it looks like: A vertical opening or rotted-out pocket on the trunk, often where a major limb used to be. Squirrels and raccoons love them, which is why most homeowners spot the wildlife traffic before the cavity.

Why it matters: Trees are resilient to hollows because the outer ring of wood does most of the structural work. The rule of thumb: if the solid wood remaining is less than a third of the trunk diameter at the cavity height, the tree is a candidate for removal. More than that, and we usually keep it.

What it predicts: Trunk failure through the cavity during a wind event from the side that points the cavity at the prevailing wind. Expect splitting wood, hanging strips, and a tree across whatever is downwind.

Can pruning fix it? Sometimes. A crown reduction prune can drop the lever arm enough to keep a tree with a high cavity standing for years. If the cavity is at the base or in a major fork, prune the dead weight and accept that the tree is on a clock.

2. Mushroom conks or shelf fungus at the base or on the trunk

What it looks like: Hard, shelf-shaped fungal growths on the trunk, or soft punky mushrooms at the soil line. The two we see most often in Ontario: Ganoderma applanatum (artist's conk, big flat brown shelves at the base of maples and beeches) and Armillaria (honey-coloured mushrooms in clumps at the root flare in fall).

Why it matters: The mushroom is the fruiting body of a fungus that has been eating the structural wood inside the tree for years. By the time a Ganoderma conk shows up on a sugar maple in Etobicoke, the lower trunk and root buttress are usually already compromised. Cut the conk off, the decay keeps spreading.

What it predicts: Root or root-collar failure. The tree goes over, root plate and all, in saturated soil after rain. This is the failure mode that flattens fences and lands across driveways without warning.

Can pruning fix it? No. When we see conks at the base of a mature tree over a target, we recommend removal in nine cases out of ten.

3. A root plate lifting or soil heaving on one side

What it looks like: A crescent-shaped crack or hump in the soil on the opposite side from the lean. The grass might be torn. Sometimes you can see the top of a root that used to be buried. After a storm the heave is obvious within an hour.

Why it matters: This is the most urgent sign on the list. A lifted root plate means the tree is actively rotating in the soil. The fibres on the tension side (away from the lean) are tearing. Once that starts, the tree finishes the job during the next wind event, sometimes during a calm afternoon if the soil keeps loosening.

What it predicts: Whole-tree failure in the direction of the lean. Distance covered roughly equals the height of the tree. If your house, garage, or hydro line is in that arc, this is a same-day call.

What we do: Tape off the drop zone. If our crew can get to it the same business day, we will. Root-failure trees are the bulk of our emergency tree service work in Toronto, Mississauga, and Burlington after every major windstorm.

4. A sudden new lean that was not there last year

What it looks like: Compare a photo from a year ago with the tree today. A lean that has been there since the tree was planted is usually a static problem. A lean that appeared in the last 12 months is a moving problem.

Why it matters: Trees live with a long-standing lean because they grow reaction wood (denser wood) on the compression side to compensate. A new lean means the support system has changed faster than the tree can react. The change is almost always at the root.

What it predicts: Same failure mode as the lifted root plate above. The difference: a sudden lean often still has intact bark around the base, so it looks less alarming than a heaved root. Do not let appearance fool you. The internal damage is the same.

Quick check: Stand 30 feet from the tree on a calm day. Hold a phone vertically at arm's length and line up the screen edge with the trunk. Anything over 15 degrees on a mature tree with no historical lean is a call.

5. More than 25% of the canopy is dead

What it looks like: Walk around the tree and count the major limbs that are bare in mid-summer. If more than a quarter of the canopy has no leaves in July, the tree is in active decline.

Why it matters: Crown dieback is the tree telling you the plumbing has stopped working. The vascular tissue under the bark cannot push enough water and sugar to the canopy. That is sometimes a fixable problem (compacted soil, restricted root zone, construction damage) and sometimes the start of structural failure.

What it predicts: The dead branches themselves fall first, often in 20 km/h winds that healthy branches shrug off. Once dieback passes 50%, whole-tree failure becomes likely because the live canopy on the other side is now an unbalanced lever.

Ash trees are a special case: An ash with more than 25% crown dieback in Ontario is almost certainly emerald ash borer, and the prognosis is different. Read that post first, then book the visit.

6. A crack in the trunk that continues into the soil

What it looks like: A vertical split in the bark, often hairline at the top and widening as it goes down. The diagnostic detail: the crack does not stop at the soil line. Brush the mulch aside and see if you can trace it past the root flare.

Why it matters: Trunk cracks that stop above grade are usually old freeze cracks or sun-scald injuries the tree can compartmentalize around. A crack that runs from the trunk into the soil means the failure has already started underground.

What it predicts: Whole-tree failure along the crack's plane. Often happens during the first major load event after the crack appears. Wind, ice, or a heavy summer rain on a fully-leafed canopy can be enough.

Can pruning fix it? No. We have seen removals in Hamilton and Oakville where the homeowner spotted a trunk-to-soil crack on a Friday and the tree was down across the driveway by Monday. If the crack reaches the ground, the tree is past saving.

7. Included bark at a major fork in the trunk

What it looks like: A tight V-shape where two stems meet, with a dark seam of bark pinched between them instead of a smooth U-shaped union. Common on Norway maples, silver maples, and any tree that was topped or improperly pruned when young.

Why it matters: A proper U-shaped union grows wood that knits the two stems together. A V-union with included bark grows two competing trunks sharing only a thin strip of contact wood. Once one stem leans, twists, or takes ice load, the seam splits and one half of the tree comes down.

What it predicts: Half-tree failure, usually during ice storms or wet snow events. Common after Ontario's freezing rain weeks in late December and early January. The remaining half is usually unbalanced and unsalvageable.

Can pruning fix it? Sometimes. If we catch a V-union early on a younger tree, a structural prune (cabling, weight reduction on one stem) can buy decades. On a mature tree with a 60-foot included-bark fork over your roof, the safer answer is removing one stem or the whole tree before it picks the timing itself.

Two things that change everything: what is underneath, and what the tree has already done

Target value: A 90% dead silver maple at the back of a 2-acre lot in Kitchener with nothing under it can stay for wildlife. The same tree over a driveway or a kids play structure in Whitby moves to the top of the removal list. Defect with no target is patience. Defect with a target is action.

History of failure: The single best predictor of the next limb coming down is whether one already has. If a major limb dropped in the last three years on a tree with structural issues, the odds of the next failure are higher than any textbook model suggests.

What a hazard tree assessment actually involves

On a typical visit: We walk the tree from a distance first to read the lean and canopy. Then we get close, check the root flare, sound the trunk with a mallet (a hollow thud tells us where the cavity boundary is), photograph defects, and measure the dimensions that go on the report.

What you get: A written assessment with the defect, the target, the likely failure mode, the recommended action (prune, cable, monitor, or remove), and a timeline. If the tree is above a Toronto bylaw threshold, we will tell you whether a permit is required and we can file it for you.

Cost question: Hazard tree assessments are usually a flat-fee visit, separate from the removal quote. Most homeowners book the assessment, get the recommendation, then book the work as a follow-up. Sometimes the assessment finds nothing actionable and you go back to ignoring the tree, which is the best possible outcome.

When to call us this week, and when to wait

Call us this week if you see lifted soil, a sudden new lean, a trunk crack reaching the ground, mushroom conks at the base, or any tree over a target with more than 25% dead canopy. These are the signs that move fast under load.

Watch and book within a month if you have a hollow cavity that has been there for years, an included-bark V-union without visible cracking, or a long-standing lean that has not changed. Worth a professional eye, but you are not racing the next storm.

The honest truth: Most of the calls we run turn out to be one or two defects on one tree, not the worst-case scenario the homeowner pictured at 2 a.m. The point of learning the signs a tree might fall is not to panic. It is to know which observations get you on the schedule today and which can wait.