Dr. Lew Feldman, Garden Director
What are knots and knotholes and how do they form?
Knots are visible imperfections in wood. They are typically circular and darker than the surrounding wood area and when the knot separates from the surrounding wood a knothole form. Let’s consider how knots and knotholes originate.
The explanation begins by observing the trunks of trees, as can be viewed in the UC Botanical Garden’s Redwood Grove. You’ll notice that the lower portions of the tree trunk often show dead, branches, which as a consequence are no longer elongating (blue arrow).
As time passes and the tree increases in width/diameter the dead branch is engulfed in and covered by the expanding, newly produced wood (illustrated in the diagram below by the movement apart of the red lines).
Sawing a tree trunk parallel to its long axis (indicated above by the dashed line in the far right panel, and below) reveals the knot.
So next time you are in a knotty pine-paneled room, have a close look at the individual knots and ask yourself, what feature reveals that they are embedded branches.