Stop Rot in a Tree Trunk Hole
Roger Cook gives advice on what to do with tree-trunk holes that show decay
Q: I have a maple tree with a hole in the trunk where a limb was removed. There is some decay in the hole. Is there anything I can do to stop the rot? —William Ellington, Wake Forest, N.C.
The only way to stop rot is to prevent water from getting into the hole, either by capping it with metal or plugging it with spray foam. If the rot isn't too advanced, the tree may have a chance of recovering.
Before you do anything, call an arborist to make an assessment. He or she can evaluate the tree's overall health, see how much damage has occurred, and determine whether cables are needed to stabilize limbs.
If you decide to cap the hole, start by scraping out as much of the soft, rotted wood as you can. Then cover the hole with a piece of aluminum sheet metal, which won't rust. Cut it so that it overlaps the edges of the hole by a half inch or so, then bed the metal in a fat bead of silicone sealant and tack it in place with a few 1¼-inch stainless-steel siding nails. You can paint the patch to blend in with the rest of the trunk.
If you seal the hole with foam, remove the rotted wood first, then use a canned spray that's formulated to fill big gaps. Once it hardens, trim the excess so that it will shed water. And be sure to paint the plug; sunlight breaks down unprotected foam.
— This Old House landscape contractor Roger Cook