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New Approach to Pruning

Shigo has found that as trees grow, they form natural barrier zones at the base of each branch that, should storm damage or branch removal by pruning occur, provide built-in protection from such invading organisms as decay and cankers.  This barrier zone is not at the exact point where branch or trunk (stem) appear united when viewed from the outside.  The barrier zone actually is a short distance (usually less than one inch) away from the trunk.  Thus, when a branch is "flush cut" as previously recommended, the natural barrier is removed.

To identify the barrier zone, look at a branch closely.  Near the base of the branch will be a distinct swelling or "collar" and often a ridge of bark that is distinct from the bark areas on either side.  This ridge varies according to the angle of the branch as it is attached to the stem.  The barrier zone is located in the collar area outside of the branch bark ridge.  Thus, when you prune away a branch, always cut just outside of this collar to preserve the barrier zone.

Some trees do not have a distinct collar and ridge that completely circles the branch.  In these cases, locate an area on the branch that is distinct and make your cut at a right angle to the branch.

Depending upon the tree type, this procedure often will leave a knob or very slight stub.  Do not, however, leave stubs beyond the collar.  Such stubs will die back and allow decay organisms to get a "foothold" and enter the tree.

Not All Branches are Branches

Most trees have a central trunk, but this trunk often divides into several stems that appear to be branches.  These are referred to as codominant stems.  If a stem cut must be made, always cut outside of the bark ridge.

It is important to avoid removal of stems, where possible, because no natural barrier zone is present where two or more stems join.  Organisms have an easier time invading such cuts.  Pruning out codominant stems also tends to promote weak sucker growth (water sprouts).  Avoid topping or pollarding any tree!

Large Branch Removal

When removing large branches, first make an undercut several inches outside of the collar.  Next, remove the limb with a second cut an inch or so outside of the undercut.  This removes the limb weight and prevents stripping of the bark when the limb falls.  The third cut should be made just outside of the collar as described above.

Safety First

If you need to climb more than a step ladder, or the tree limbs to be removed are large or may fall onto utility wires or a structure, it is best to hire a bonded, professional tree company to do the job.

Wound Dressings Not Useful

Wound dressings have been shown to interfere with the natural development of callus tissues that eventually close the pruning wound.  In some cases, wound dressings can even harbor disease organisms much like what occurs when a Band-Aid is left on a skin cut too long.  It is far more important to make the cut smooth, outside of the collar and allow the wound area to dry.

If a would dressing is desired for aesthetic purposes, use a very thin coat, just enough to darken the wound area.  The best are the aerosol sprays of water-emulsified asphalt sold in garden centers.  Do not use oil-base paints, thick tars, or other materials containing petroleum solvents.

Maintain Tree Health

The key to good wound closure following pruning is to maintain a healthy tree through proper watering, fertilizer application and pest control.  Trees under stress from drought, over watering,  pest attack, lawnmower and other mechanical damage, and poor nutrition cannot successfully fight off invasion of organisms.

For other information on maintaining tree health, managing pests and proper watering practices, consult the Colorado State University Cooperative Extension office in your county for other Service in Action sheets.

Courtesy of the Colorado State University Cooperative Extension (6/85)

    by James A. Feucht