Improving Nebari
Coping with "flying buttress" roots on hornbeam


European Hornbeam (Carpinus betulus) have sinuous trunks which become fluted with age.
But they do have an annoying tendency to throw out long, straight, rigid roots
from just above the original seed roots. This is particularly common with nursery-grown plants,
after they have been planted too deep in their containers.


 

Top right:
Although the roots on this hornbeam are well-distributed and a good thickness considering the age of the tree (about 25 years), they are horribly straight and rigid. Two other factors made matters worse. First, there was a heavy, horizontal root below the trunk, and second, as the mass of roots within the pot increased, they thrust the tree higher and exposed even more root. Something had to be done.

Bending hornbeam roots is out of the question. "Hornbeam" in ye olde English meant "hard wood" - and they weren't kidding! The solution lies beneath the soil.

Centre right:
Before embarking on any major surgery, it was important to ascertain precisely how much lower in the pot the tree needed to be to make the roots acceptable. I made a frame of light wood and began filling it with pine bark chips until the new "soil" level was right.

Hmmm! 40mm (one and three quarter inches) - that's a lot! I resolved to give it my best shot. After all, the pot was perfect for the tree and replacing it with a deeper one would be less than ideal (as well as expensive).

Bottom right:
This picture shows the cut area of heavy root.

Trees grown from seedlings frequently display this characteristic. Seeds are almost never sown the right way up - nature doesn't work that way and commercial propagators certainly don't! As the seeds germinate, the root responds to geotropism and curves downward and the stem curves to grow upward. This causes a horizontal section of root/stem below the soil.

I should really have cut this root off entirely when I first repotted, but I judged there was insufficient root remaining to sustain the tree. Even now, after twelve or so years, total removal of the offending root would be taking an unacceptable risk. So I shaved the required 40mm off with a reciprocating power chisel (Ryobi). This tool is perfect for working with wet wood as it cuts beautifully cleanly and won't clog like rotary carving bits.

In fact, I cut away rather more than the required 40mm, because I knew that during the next few years the healing callus would wrap around the exposed wood and, once more, begin to push the tree out of the pot. Next repotting time, I'll see if enough new root had been generated from the ends of the visible nebari to allow me to dispense with the offending chunk once and for all.

Below:
The hornbeam's new nebari.