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How to Fill Cavities in a Tree

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Tree cavities are holes in a tree trunk that can vary in diameter and depth. These cavities often occur naturally, but can occasionally endanger the tree structurally, or provide a home for ants, hornets or mosquitos due to the collection of standing water. Tree experts often recommend against filling a tree cavity because it can make the tree unstable over time. If you find it necessary to fill your tree’s cavities, use expandable foam to help support the tree and prevent moisture from entering the hole.

Step 1

Position a ladder beneath the hole, if necessary, to reach it. Ascend the ladder until you can comfortably reach the cavity. Check the interior of the cavity with a flashlight to ensure no animals are residing within it before you fill the hole. Any living animals may try to chew through another section of the tree and damage the trunk if the hole is filled with them still inside. Inspect the hole for any standing water. If water is present, allow it to dry before using the foam.

Step 2

Check the sides of the hole and the bottom for any rotting or dead bark. Use the tip of a screwdriver to chip away the material.

Step 3

Take off the top of an expanding spray foam can. Attach the tube to the can's nozzle and shake the can vigorously for approximately 20 seconds.

Step 4

Position the foam can tube as close to the cavity’s center as possible. Depress the top of the can's nozzle to dispense the foam. Release the nozzle once the cavity is approximately 50 percent filled with the foam.

Step 5

Use a clean rag or paper towels to wipe off any excess or spilled foam outside the cavity immediately. The foam can stain the tree once dried. Give the foam 15 minutes to expand.

Step 6

Check to ensure the foam has expanded to completely fill the cavity. If space remains inside the hole, spray small amounts of foam and wait for it to expand. Continue this process until the hole is filled.

Step 7

Allow the foam to harden overnight. Use a sharp knife to slice away any foam that may have expanded outside of the cavity.

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