How to tell if a tree is dangerous
A dangerous tree does not always look dangerous. Some of the clearest warning signs are at the base, hidden by shrubs, or high up where you rarely look. This guide covers what to check and when to stop looking and call someone.
Look at the ground first
The most important thing to check is where the trunk meets the ground. A sound tree flares out where the roots spread, and it does not move when the wind blows. A tree with a problem often tells you at that point before anywhere else.
Look for a mound of soil lifting on one side of the trunk, or a crack in the ground running away from the tree. That is usually the sign of a root plate that has begun to move, and it is common after a wet season. Look too for a hollow at the base, soft or crumbly wood, or mushrooms growing from the trunk, all of which point to decay inside.
Look up the trunk
Scan the trunk for splits, especially where it forks into two or more stems. A fork that has a crack running down the middle, or a deep fold of bark forming between the stems, is a weak point. Where two heavy stems grow from the same fork, the weight of a full crown rests on a joint that may be failing.
Look for dead wood: bare branches with no leaves in season, or bark that has fallen away. Look for a limb that has already broken and is caught in the crown, which is both a sign of weakness and a hazard waiting to drop.
Look at the crown
A tree that is thinning at the top, or losing leaves earlier than the trees around it, is often under stress. A crown that has grown noticeably one-sided, or a tree that has leaned further than you remember, is worth a second look. So is a tree that has shed several large limbs in the recent past.
If a tree has just shed a heavy branch without any obvious reason, do not assume the problem is over. What is left behind in the crown may be weaker than it looks.
Think about what is under it
The same tree can be safe in an open field and dangerous in a garden. What decides it is not just the tree's condition but what it would hit. A tree leaning over a bed of shrubs is one thing; the same tree leaning over a bedroom, a driveway or a power line is another matter.
Do the plain calculation: if this tree failed on a windy night, what would it land on? If the answer worries you, the tree deserves a proper look regardless of how healthy it appears.
What not to do
Do not cut a dangerous tree yourself, and do not climb it. Do not cut a limb that is leaning or under tension, and do not use a ladder near a tree that is unstable. Most serious tree accidents involve homeowners and chainsaws, and the tree that ends up hurting someone is usually the one that looked manageable.
If a tree is touching a power line, do not go near it at all. Treat the line as live and phone the utility.
When to get a contractor out
Get a contractor to look at any tree with a lifted root plate, a split trunk, a hollow base or a lean that has changed. Get one out for a tree that has shed large limbs, and for any tree standing over a building, a driveway or a boundary. Before the storm season is also a sensible time to have mature trees checked, because the work is easier in calm weather than in the middle of a storm.
This page is general information, not a substitute for a professional inspection. A contractor can judge what you cannot see from the ground, and can tell you whether the tree needs pruning, removal or nothing at all.
Frequently asked questions
What is the clearest sign a tree is dangerous?
A root plate that has lifted, leaving soil mounded or cracked at the base, is one of the clearest. A split fork or a hollow base is also serious.
Can a tree be saved if it is leaning?
Sometimes, if the root plate is sound and only the crown leans. If the lean followed heavy rain, have it looked at soon.
Should I prune a dangerous tree myself?
No. Cutting a limb under tension is one of the most common causes of serious injury. Leave it to someone with the right gear.
How often should mature trees be checked?
It is sensible to have large trees looked at before the storm season each year, or sooner if something changes.
Is a tree with dead branches always dangerous?
Not always, but dead wood in the crown will fall eventually. Removing it is usually a straightforward pruning job.