Sealing a Wounded Tree

Tree Wounds and Their Dangers

• Kids only have two arms and look at all the breaks and scratches they suffer, so it comes as no surprise that trees, with their myriad, outstretched branches, also suffer wounds. Trees break branches, get smacked by moving vehicles, get scraped or chewed by animals or burned by fire. When an injury breaks a tree's bark, it exposes the inner back and core of the tree to bacteria and fungi infections; the resulting decay can weaken or even kill a tree.

Wound Sealant

• Wound sealant was, for years, considered the best treatment for tree wounds and it is not difficult to locate older articles online recommending it. Given the dangers of tree infection and decay, sealing over the wound to keep the pathogens out and give the tree a chance to heal feels intuitively correct, like a band-aid on a child's knee. But horticulturists have learned that trees do not heal like children.

Trees Seal Rather Than Heal

• Trees do not heal wounds like humans do, from the inside out. Rather, a tree closes a wound by sealing it off by growing specialized callus tissue. This tissue begins growing on the edges of the wound and eventually covers the entire area. Experts at Texas A&M University say that a wounded tree will also chemically alter the wood around the injury to make it impenetrable to decay and infection.

Sealants Interfere

• No research establishes that wound dressings or sealants heal tree tissue, according to University of California experts. Rather, these products can impede a wounded tree from putting its own protections in place. Sealants can even encourage decay by creating a protected area inside the covered tree wound where pathogens can grow.

Exception to Rule

• Like every good rule, the no-sealant principal has an exception: sealant should be used on oak trees subject to oak wilt disease such as black oak (Quercus velutina) that thrives in U.S. Department of Agriculture plant hardiness zones 4 though 8. You should apply tree-wound sealant to these oaks' pruning wounds immediately after pruning. Oak wilt disease is a fatal infection spread by wood-boring beetles that are attracted to oak tree sap. Covering the pruning wounds with a sealant made especially for the purpose is one way of preventing the spread of this dreaded disease.