You approach the overgrown forsythia on hands and knees, cutting out
perimeter canes lying on the ground, and thus forcing it to flow upward
like a fountain. Cut out old, dead stubbed-off canes at the base.
You'll know they are dead because they don't have any side branches
growing off of them. Mostly they are so old as to be punky and you
can just yank them out with your hand. Sometimes I just step on an
old dead stub and lean into it. It just snaps out. (In trees
the removal of dead limbs is sometimes referred to as Oregon Boot
Pruning.) Continue pruning by working your way up and out, moving
in a roughly spiral fashion. Take out dead wood, and crossing/rubbing
branches. Take out a few canes that crowd up the center, sometimes
sawing with just the topics of your blade. Spend a lot of time moving
around getting into position for the best cut. Crawl outside the
shrub and walk around it every so often to judge your progress and plan
your next avenue of attack. Why? One, you may see how much
things are improving already and be encouraged to continue, or Two,
you may see that things are getting very thin on one side and decide
to move to the other before you over-thin the entire shrub. Remember,
you never can get it to look perfect from all sides, so quit while you're
ahead. In point of fact, almost all branches in a forsythia are
rubbing and crossing. This generally discourages the new pruner.
Often he or she just gives up, cuts off the top and goes back inside the house
to fix a nice hot cup of cocoa. But remember the job is not to
eliminate wrong branches, just reduce the number of them. It doesn't
even really matter which ones you choose. You could blindfold
yourself, throw six darts into the forsythia bush, cut out the darted ones,
and it would miraculously look a lot better. So don't worry about which
cane is the right one, just make yourself cut, and keep moving around.
There is nothing that you can do to a mature forsythia (heading or over
thinning) that you can't get back. So be brave. As an old client
of mine says, "Prune with vigor." Forsythias are really, really tough,
and can always renew themselves with new canes.