I recently told a novice pruner to go get the latest update of WI's
extension publication on how to make proper pruning cuts, because it was an
outline of Alex Shigo's recommendations. Yes, I got the Blank Stare, but
the pruner acquired the publication.
Shigo is (was?) an arborist who decided to research & figure out why some
pruning cuts "heal over" while others turn into big gaping rotten hollow
branches & trees. You've really got to be interested in this to read one of
his books entirely, but shorter pamphlets & publications illustrating the
highlights are popping up everywhere. If your local extension publication
mentions branch bark ridge, branch collar, included bark, & excluded bark,
you're probably on the right track.
Shigo's general recommendation on timing of pruning is "not while the leaves
are forming or falling"-- rapid spring growth and autumn senesence.
Tanis Cuff, who is noticing how much faster the pruning cuts close since
I've tried to follow Shigo's recommendations