Takes courage to cut a precious Japanese maple
We score a hit when readers report: I was afraid to cut my
Japanese maple but after seeing you prune, then helping you do it
in a hands on session and seeing pictures of other real trees that
had been cut (and lived), it all finally added up to give me
courage to prune.
This Japanese maple got its skirts lifted and crown reduced
in a Garden By Janet & Steven session during a January thaw.
Its gardener explained the need this way, "I already moved the
walkway so it could have room. I don't want to move the walk again
so we'd better prune it."
Here are before and after shots, above, with dog Maggie telling
us ""Enough, stay away now!"
We aimed to shorten all the branches by two times the growth
rate (branch extension rate). That will allow the tree to grow for
a couple of years before reaching the edges of its allotted space
once again. But first we evaluated the main branches and decides
there was an extra one here. Arrow. It did nothing but cross over
and through spaces the other three main limbs should have had all
for their own.
We tied up the target limb's branches so we could step back,
look at the string-marked wood and decide if we could live with
what could be left after taking that trunk out.
In addition, the three we eventually designated as "keepers"
describe graceful curves, like arms of a pinwheel.
Gone! The whole extra trunk, removed. 
Before, and after. Is it smaller -- less wide? Yes. Is its
structure graceful, visible, and able to be enjoyed? Yes. Did we
cut off too much? No, only 1/3 the leaf buds went into yard waste
bags.