Callus

Callus is what plants use instead of bandages.

​What are tree wounds?

Tree wounds can occur on purpose, by pruning, or by accident, from heavy winds or by being overladen with fruit. Most pruning cuts are relatively smooth. Accidental wounds tend to be jagged and the bark may be torn down the trunk. In these cases, the tree will benefit from the branch being cut back to a place where a flat wound is possible. This gets rid of insect hiding places and speeds the healing process for the tree. In both cases, interior tissue is exposed to the elements.

​Traditional wound treatment

For decades, people have said that we should protect tree wounds with paint, pastes, and salves, which are generally petroleum based. 

Tree callus (Krzysztof Ziarnek, Kenraiz) CC BY-SA 4.0

The idea behind these treatments was that an open wound was vulnerable and that we could ‘help’ our trees by painting the cut surface with tar, asphalt, wound paint, or some other sealant. Instead of providing protection, these treatments actually seal in harmful bacteria and fungi, increasing the chance of disease or decay. Also, there are certain disease-carrying organisms that love to feed on or are otherwise attracted to the sealant!

Natural remedies

It ends up, trees already know how to protect themselves. Just as our skin forms a callus in response to hard work and friction, trees create tissue over wounds to protect themselves from pests and diseases. The word ‘callus’ is from the late Middle English Latin word ‘callosus’ which means ‘hard-skinned’. Trees are able to generate their own ‘hard skin’ to cover a wound. If that process is interrupted with oil-based sealants, the internal processes of decay prevention may also be interrupted.

An exception to the rule

One case where wound dressing is a good idea is in regions (like ours) where oak wilt is a problem. If an oak in these areas is damaged or requires pruning, a sealant that contains insecticide and fungicide can prevent loss of the tree.