How to Tell if a Tree is Rotten Inside - Your Complete Guide

Published on February 3, 2024

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how to tell if tree is rotten inside

Trees seem strong and steady, firmly planted in the ground. But when decay fungi and wood-boring insects attack, they can secretly hollow out the insides, leaving merely a thin shell of wood. By the time major signs appear, the tree may already have extreme structural weakness and risk of failure. 

So, how can you tell if a tree is rotten inside? Look for subtle early clues of interior rot, including holes, oozing sap or liquids, fungal growth, insect infestation, or root issues. You can complete tests to learn more, but you should also seek the advice of an arborist.

When safety and property protection are paramount, arming yourself with inspection knowledge is key. Read on to learn the best methods for tree care for unseen rot to keep your landscape trees standing tall.

Look for Signs of Decay on the Outside

The first place to check for rot is on the outside of the tree. Look for these signs:

  • Holes or hollow spots in the trunk or branches - This can indicate fungal decay or carpenter ants tunneling inside. Gently poke the holes with a stick to see if there is soft, crumbly wood inside.
  • Oozing liquid or sap—Dark-colored wet areas indicate slime flux or bacterial wetwood decay, which causes foul odors.
  • Fungal growth—Mushrooms or conks growing on the bark are caused by fungi that decay wood. They often indicate major rot inside.
  • Cracks or splits in bark—Long vertical cracks or peeling bark can indicate a hollow trunk. These allow entry points for fungi.
  • Dead branches - Look in the upper crown for dead twigs and branches, which indicate the tree is under stress.

If you see these warning signs, continue inspecting the tree for further signs of interior rot.

How to Tell if Tree is Rotten Inside? Check the Tree Trunk

Examining the wood of the tree trunk is important for determining soundness.

  • Drill test - Use an increment borer to extract a sample wood core. Crumbly, soft-core wood means advanced decay.
  • Poke test - Use an awl, screwdriver, or pickaroon to poke the trunk. If you meet no resistance, it’s mostly hollow inside.
  • Rocking test - Push the tree gently from different angles to see if the trunk rocks at the base. Movement indicates root or butt rot.

Use these methods around the trunk circumference, checking higher up as well. Take note if certain areas seem more degraded.

Inspect the Soil and Roots

Signs of advanced rot often manifest around the soil line and roots. Look for:

  • Conks or mushrooms - Fungal fruiting bodies here indicate butt or root rot. The fungus may permeate the roots and heartwood.
  • Insects - Termites, carpenter ants, or beetle grubs chewing on roots or the trunk base. Their presence almost certainly means rot.
  • Old wounds include cankers, scars from past branch rips, or damaged root flares. Over time, these allow decay to enter the interior wood.
  • Root issues - Girdling roots choking other roots or dead/absent roots on one side. These situations restrict nutrient and water flow, leading to canopy dieback.

Major root or soil line defects suggest structural instability and deficiency throughout the tree.

tall tree trimming

Assess the Tree Canopy

The crown area should be full, proportional, and show no more than 10% dieback.

  • Dead branches - Look for dead tips and whole branches that indicate rot or hollowness progressing from the main stem.
  • Sparse foliage - thin overall crown or single bare branches signal disease or nutrients unable to reach those areas.
  • Off-color - yellowing or browning leaves reveal stress and reduced vascular flow.
  • Leaf undersides are chewed by leaf miners or spotted by fungus and bacteria, which relates to poor tree vigor.

Take note if foliage loss is on just one side. That area of the trunk likely contains advanced rot.

Consider the Tree Species

Certain tree species are more susceptible to decay fungi and environmental hazards. Assess your risks based on type.

High-Risk Trees: Ash, Aspen, Beech, Birch, Black Locust, Cherry, Cottonwood, Elm, Hemlock, Maple, Spruce, Willow

Medium-Risk Trees: Fir, Oak, Pine, Black Walnut

Low-Risk Trees: Cedar, Honeylocust, Magnolia, Mulberry, Redwood

Species with naturally thin bark and water/insect vulnerabilities tend to rot easiest. However, inspect any tree with caution, regardless of tendencies.

Bring in a Professional Arborist

If your tree shows multiple signs of extensive decay, the safest option is to consult an ISA-certified arborist. They have the specialized tools and expertise to diagnose internal deterioration fully.

They can provide a resistance drill test, decay mapping, trunk sounding, aerial inspection, fungus identification, and CT assessment. An arborist does a full risk analysis before recommending treatment or removal.

professional arborist assessing tree

Wrapping Things Up

Catching decay interior decay in trees early is critical for preventing tree failures that damage property, vehicles, and people. However, understanding health signs versus disease symptoms takes dedicated observation and awareness. Utilize all your senses while systematically checking trees from the soil to the canopy for deficiencies. Make it a habit to walk around your landscape after storms, seasonal changes, or annually. 

When you spot downward trends, take prompt restorative action or call an arborist. Keep trees vigorous with proper care and pruning. Though all trees eventually weaken with age, arm yourself with detection skills so you can intervene at the first stage of decline. Stay proactive in your stewardship over the towering life in your yard. With regular inspection and responsiveness, you can maximize trees’ longevity as assets that enrich your property.

About West Bloomfield Tree Service & Removal

At West Bloomfield Tree Service & Removal, we have seen firsthand the damage rotting trees can cause. With certified arborists on staff and specialized tools at our disposal, West Bloomfield Tree Service offers comprehensive inspections to diagnose internal decay in your landscape trees. If you notice any concerning signs in your trees, don't hesitate to pick up the phone and call our team today at (248) 487-1721 for reliable rot detection and treatment.


How can you tell if a tree is hollow inside?

Obvious external signs like holes, cracks, or missing bark often indicate interior hollowness and decay. Performing a "poke test" by pressing a pole into the trunk can reveal whether you meet resistance or easily enter an internal void. Trees that rock back and forth at the base when pushed gently are likely hollow inside the butt area or suffer from severe root rot underneath.

How do you test a tree for rot?

An increment borer extracts a wood core sample so you can directly examine the wood condition and the presence of fungus. The "drill resistance" method uses a power drill to assess how easily the bit penetrates suspected areas of decay. Additionally, an arborist can perform a sonic tomography test, using sound waves to create an image that maps decay pockets within the tree.

How do you tell if a tree is truly dead?

A dead tree will have no signs of growth, no foliage or mushroom formations, and the bark easily peels away to reveal dry, brittle wood underneath. Scrape off some outer bark with a knife - living cambium layer wood should be moist, greenish, and resilient rather than crisp and brown. Tap or push on dead trunks and larger branches to determine if they remain rigid, as degradation will make them saggy; any portion that stays upright on its own still contains sound wood.

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