How to look over trees near the house and lines
To tell if a tree is dangerous, walk around every large tree that could reach your house, driveway or power lines and check it for large dead branches, cracks, cavities, mushrooms at the base, leaning and recent root damage. If you see any of these, have an ISA Certified Arborist examine it. Never touch branches near power lines.
How to tell if a tree is dangerous to your house
Tree risk has two parts: a weakness in the tree and something it could hit. The International Society of Arboriculture (ISA) says no tree is completely safe, but only a small number of the trees that fall hit anything. A defect over an empty field matters far less than the same defect over your bedroom.
You can move a car or a picnic table out of the way. You can't move a house or a power line, so those trees get your attention first. ISA also says keeping others safe around trees on your property is the owner's responsibility. Ask your insurer or a local attorney if a neighbor's tree or yours is at the center of a dispute.
Your job is to spot warning signs, not to rate them. ISA says judging how serious a defect is should be left to a professional arborist. Older and larger trees are more likely to drop branches, and hidden decay may need an arborist's instruments to find.
How to tell if a tree is dangerous, step by step
- List the trees that matter
Include any tree tall enough to reach the house, garage, driveway, a neighbor's property or the wires coming to your home.
- Start with the crown
Stand back with binoculars. Look for dead limbs, hanging branches, thin patches and leaves that look wrong for the season.
- Circle the trunk
Look for vertical cracks, openings, cankers, wounds and bark that has come loose.
- Look at the ground
Check for cracked soil, mushrooms and cut roots. Ask yourself if anyone has dug, paved or changed the soil level nearby.
- Compare the lean
A tree that has always leaned differs from one that has started to. Take a dated photo from a fixed spot so you can compare next time.
- Look up at the wires
Note any branches near service lines, and report them to your electric provider. Don't prune them yourself.
- Repeat after big storms
Wind, ice and rain-softened soil can overturn trees or break them, so walk the yard once it's safe.
Signs a tree is dangerous and what to do about each
| What you see | Why it matters | What to do |
|---|---|---|
| Large dead branches, or broken ones still hanging | The most obvious hazard. Risk depends on size and what's below | Keep people and cars clear, then call an arborist |
| Long cracks in the trunk, major limbs or branch joints | A split can be where the tree fails | Arborist |
| Two main stems rising from one point | These split trunks are often failure points | Arborist |
| Cavities, rotten wood, loose bark or mushrooms at the base | Signs of decay | Arborist |
| Cracked or heaved soil at the base, especially with a lean | The roots may be moving, which can warn of failure | Treat as urgent. Stay out of its reach and call an arborist now |
| Yellowing, undersized leaves or a thinning crown | The tree is stressed or declining | Arborist at your next chance |
| Topping, heavy pruning, or recent digging, paving or soil changes | Weak regrowth, root loss and later decay | Arborist |
| Any part of a tree touching a utility line | It can cause outages, surges and fires, and the line may be live | Stay away and call your electric provider |
When to call an arborist and what they may recommend
ISA's rule is simple: one yes on its checklist means an ISA Certified Arborist should examine the tree. Use the Find an Arborist tool at TreesAreGood.org, then confirm the credential with its Verify a Credential tool. For a risk opinion, look for an arborist who also holds the Tree Risk Assessment Qualification.
An arborist may recommend pruning out the bad branches, adding cables or braces, routine care, or removal. Cables and braces add support, but ISA says they don't guarantee the tree won't fail. Poor pruning can weaken a tree, so don't let a price-only crew talk you into cutting the top off.
After a storm, resist the urge to cut anything yourself. Never go near a downed line, because it could still be carrying electricity. Keep clear and call your electric provider.
What homeowners say about a dangerous tree near the house
Look at branches touching the roof as well as roots near the foundation. One owner traced mice to a tree they were using to reach a roof vent. (DIY Stack Exchange, Hacker News)
Tree near power lines and other safety questions
Do mushrooms at the base mean a tree is dying?
They're a sign of decay, which ISA lists as a warning sign. They don't tell you how much of the tree is affected, so an arborist needs to examine it.
Who do I call if a tree is touching a power line?
Call your local electric provider. ISA warns never to remove branches or any tree part from or near power lines, and never to go near downed lines.
How do I know if an arborist is really certified?
Use the Verify a Credential tool on TreesAreGood.org. ISA Certified Arborists have passed an exam and must keep up continuing education to stay certified.
Sources: treesaregood.org
General guidance for U.S. homes, not professional advice. For gas, electrical and structural work, call a licensed pro.