Expressions and terms can hang on for generations (even in the pruning world), passed down and accepted without question.
Good news for those who haven't heard: Trees do not bleed. That expression refers to instances, mostly in early spring, when pruning often releases liquid from cuts . If a pruning cut is a "wound" then, naturally (in human terms) "bleeding" would follow. What this actually is, in plant physiology terms, is sap flow, a normal part of a plant's defense system. No harm is done when this occurs.
Feel better? I did.
