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Marin IJ Articles

Mastering the art and science of pruning

  • James Campbell
  • The best way to learn how to prune is to watch someone who knows what he’s doing. I learned the hard way; not understanding the art and science of aesthetic pruning can lead to problems.

    It started when I pruned my pittosporum tree. Despite good intentions, I was actually damaging my tree and unwittingly creating housing for owls and squirrels. I thought I was being neat and tidy by cutting branches flush to the bark, but I was unintentionally removing the very tissue the tree needs to heal itself and close the wound — like cutting your finger and waiting for a long and painful time for it to scab up.


    By leaving gaping wounds that could not callus over, I invited decaying fungi or phytophagous insects to move in and stay a while. These nasty invaders eat plants, ultimately killing the wood that then rots and forms a hollow in the tree — perfect for furry or feathered guests. I’m certainly not opposed to our friends that say “who,” but I prefer that it’s not in a tree that I’ve weakened to the point where it could fall on my house or, worse, on my neighbor’s home.

    I discovered my mistake — and how to correct it — from professional pruner and master gardener Gary Bartl. Bartl has a knack for teaching pruning so that it’s both educational and fun. Should you use loppers or a saw? Are there other tools worth buying? Which branches should you cut? When? Where? How? To learn all you need to know to prune anything from roses to redwoods, come to Bartl’s “Basic Pruning” talk at 10 a.m. April 29 at the Tamalpais Valley Community Center at 203 Marin Ave. in Mill Valley. The cost is $5. Participants learn what tools and techniques to use and what cuts to make — and not make.

    Using live samples and plenty of visuals, Bartl shows where the all-important branch collar is, the pruning sweet spot. As trees branch, part of the vascular system follows the branch and the remainder continues around the branch to serve other branches higher up. The overlap zone where all this happens creates a swelling. According to Bartl, this branch collar is the “circular, curved, wiggly tissue at the base of a branch.” This perfectly describes what to look or feel for when deciding where to make a pruning cut. If only I had known this before I pruned my pittosporum. In some cases, the branch collar is noticeable and in others it is hardly detectable and may be more easily felt.


    The branch collar contains active tissues that have the ability to callus over a wound and seal it off. Branch collar tissue also contains anti-microbial chemicals and phenols, which help inhibit decay while the plant heals. Think of the branch tissue as a kind of first aid kit for a tree, a Band-Aid and Neosporin all in one.

    Cutting too far out from the branch collar is almost as bad as cutting too close, but not quite. A pruning cut that leaves a stub that is beyond the reach of the tissue, that is, the opposite of cutting into the tissue like I did, means the wound is exposed too long. Fungus and bugs can move in anytime they like. Bartl shows how this is more easily corrected than a flush cut, instructing participants to simply go home and prune stubs to the outside of the branch collar where they should have been cut in the first place. Double the work? Yes. A smart preventative measure? Absolutely.

    Count on Bartl to be entertaining as he helps you get comfortable with identifying the branch collar, sheds light on other key pruning techniques and unveils how proper pruning can enhance the health and beauty of your trees and shrubs.