The Callusing of Wounds in Trees and Shrubs

Narrative and Photographs by Curtis E. Swift, Ph.D., Colorado State University Extension

an improper pruning cut

This pruning cut was improperly made as is seen by the lack of uniform growth of the callus tissue.
The dark stain and ooze is caused by bacterial wetwood

donut-like callus formation around a pruning cut

The donut-like appearance of callus (woundwood) around this wound indicates the pruning cut was made properly.

pruning wound on Honeylocust

The complete `healing' of the pruning wound on this Honeylocust demonstrates the woundwood that forms when the pruning cut is done correctly.

Trees and shrubs are often said to `heal' wounds. They do not, however, heal such damage. Humans and other members of the animal kingdom `heal' wounds by replacing damaged tissue. Trees, shrubs and other woody plants bury their wounds under new tissue. This creates a weak spot in the tree from which frost cracks can originate, insects and disease pathogens enter and disease begin.

Further information on the proper pruning of trees is available.

Placed on the Internet May 21, 1996; Updated on December 15, 2009