Unlike a tooth cavity, tree cavities are often harmless and don’t require filling. As professional arborists, we’ve seen many myths about filling tree holes. This may have come from the history of tree hole filling and its popularity. However, in today’s world, it’s recommended that you leave the tree alone and instead support it with regular tree maintenance and care.
If you’re worried about the cavities affecting your tree’s look, we’ll help identify the cause, and if it’s a good idea to fill it (safely), leave it alone, or take more serious action for your tree’s health.
What Causes Tree Cavities?
Tree cavities develop when a tree’s bark or wood is damaged. This damage can come from many different sources, including:
- Bad cuts or wounds
- Insects or animals like woodpeckers, ants, beetles, and many more
- Storm damage or lightning strikes
- Mechanical injuries from yard equipment
Over time, these wounds can create open spaces or holes in the trunk or branches of your tree. These cavities are natural, but their impact depends on the tree’s overall health. At this point, it’s best to take a step back and let your tree do its thing to protect itself if it is being harmed.
Why People Used to Fill Tree Holes
In the past, people believed that filling tree holes would protect the tree from decay and pests. They typically used harmful materials, including cement, asphalt, and even rocks. The idea was to block moisture and insects from entering the cavity. Some even drilled holes to drain water from inside the tree. Unfortunately, these methods often caused more harm than good by preventing natural movement and trapping moisture, which can speed up decay.
Expert Opinions on Filling Tree Cavities
Today, most arborists agree that filling tree holes usually does more damage than help. Trees naturally protect themselves through a process called compartmentalization, where they isolate the damaged area to prevent decay from spreading. Filling a cavity interrupts this process and can trap moisture inside, promoting fungal growth. Many professionals advise against filling tree holes unless it’s an emergency.
When Is Filling a Tree Hole Necessary?
Filling tree holes is rarely necessary. However, there are a few exceptions:
- If the hole is large and poses a safety risk, such as a hollow limb that could fall
- If filling the hole can protect a valuable or historic tree in some cases
- When a cavity is small but traps standing water, causing mosquito breeding
In cases where the cavity has led to unsafe decay or severely compromised the tree’s stability, it may become necessary to consider contacting certified tree removal services near you. Consulting with an expert tree care professional can help determine when this step is appropriate and the best course of action to protect your property.
Safe Methods for Filling (if needed)
If it’s absolutely necessary, here’s how you can safely fill a tree hole:
- Use flexible, non-toxic materials that allow the tree to move naturally. This includes expandable tree wound dressings made for tree care, flexible putty products, or natural materials like shredded bark or clean wood chips.
- Avoid hard materials like cement or foam that crack or damage the wood.
- Make sure the cavity is cleaned of loose debris, but don’t scrape away healthy wood.
- Consult an arborist for proper techniques and materials.
These methods help minimize additional harm to the tree.
Why You Shouldn’t Fill Tree Holes
While it might seem like plugging a hole would help a tree heal or stay strong, modern arborists agree that it’s usually more harmful than helpful. Getting involved with the process of compartmentalization can do more harm than good. Filling tree holes can cause:
- Increased moisture hold inside the cavity
- Damage to the tree’s natural defenses and ability to seal wounds
- Faster decay due to trapped fungi and bacteria
- Structural weakness, as the tree is unable to move naturally
Rather than protecting the tree, filling often creates conditions that speed up its decline.
The Best Ways to Care for Tree Cavities Today
Instead of sealing the hole, focus on strengthening the tree from the inside with good care practices:
- Water during dry periods to reduce stress
- Apply appropriate nutrients or fertilizers when needed
- Watch for pests or diseases and treat as needed
- Prune as needed, and with safe practices, to remove dead or weak branches
Remember: Healthy trees are better able to manage wounds on their own! That’s why it’s best to assist in a tree’s natural processes rather than interfering.
Let Nature Do Its Job
Trees are organisms that have evolved in ways to protect themselves. When a cavity forms, the tree isolates that section, preventing decay from spreading. Wildlife also benefits from cavities as homes, helping maintain ecosystem balance. Support your tree from the sidelines instead of halting its healing processes.