The Shigo 3-Step Tree Pruning Method

Prune Tree Limbs with Confidence and No Damage

Dr. Alex Shigo developed many concepts now used by practicing arborists. Most of his work was developed during his professorship and work with the United States Forest Service. His training as a tree pathologist and work on new concepts of compartmentalization ideas eventually led to many changes and additions to commercial tree care practices.

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Understanding Branch Connection

worker pruning tree
A worker during pruning on the Atlantic Forest. (Diego Lezama/Getty Images)

Shigo pioneered the now accepted way to prune a tree using three branch cuts.

He insisted that pruning cuts should be made so that only branch tissue is removed and stem or trunk tissue is left undamaged. At the point where the branch attaches to the stem, branch and stem tissues remain separate and react to a cut differently. If only branch tissues are cut when pruning, the stem tissues of the tree will probably not become decayed. The living cells surrounding the wound will heal quickly and ultimately the injury will seal properly and more effectively.

To find the proper place to cut a branch, look for the branch collar that grows from the stem tissue at the underside of the base of the branch. On the upper surface, there is usually a branch bark ridge that runs (more or less) parallel to the branch angle, along the stem of the tree. A proper pruning cut does not damage either the branch bark ridge or the branch collar.

A proper cut begins just outside the branch bark ridge and angles down away from the stem of the tree, avoiding injury to the branch collar. Make the cut as close as possible to the stem in the branch joint, but outside the branch bark ridge, so that stem tissue is not injured and the wound can seal in the shortest time possible. If the cut is too far from the stem and leaving a branch stub, the branch tissue usually dies and wound-wood forms from the stem tissue. Wound closure will be delayed because the wound-wood must seal over the stub that was left.

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Prune a Tree Branch Using Three Cuts

Tree Prune Method.

You are attempting to create or maintain a complete ring of callus or wound-wood results from a proper pruning cut. Flush cuts made inside the branch bark ridge or branch collar result in the production of a desirable amount of wound-wood on the sides of the pruning wounds with very little wound-wood forming on the top or bottom.

Avoid cuts that leave a partial branch called a stub. Stub cuts result in the death of the remaining branch and wound-wood forms around the base from stem tissues. When pruning small branches with hand pruners, make sure the tools are sharp enough to cut the branches cleanly without tearing. Branches large enough to require saws should be supported with one hand while the cuts are made (to avoid pinching the saw). If the branch is too large to support, make a three-step pruning cut to prevent the bark from ripping or peeling down into good bark (see image).

The Three Step Method for Properly Trimming a Tree Limb:

  1. The first cut is a shallow notch made on the underside of the branch, up and outside but next to the branch collar. This should be .5 to 1.5 inches deep depending on the size of the branch. This cut will prevent a falling branch from tearing the stem tissue as it pulls away from the tree.
  2. The second cut should be outside the first cut. You should cut all the way through the branch, leaving a short stub. The bottom notch stops any stripping bark.
  3. The stub is then cut off just outside the upper branch bark ridge and down just outside the branch collar. It is not recommended by many arborists that you paint the wound as that can impede healing and, at best, is a waste of time and paint.

The quality of pruning cuts can be evaluated by examining pruning wounds after one growing season. The callus ring enlarges and encloses the wound over time.