I have a 40 year old Rhododendron that needs to be trimmed back a bit.

http://homeguides.sfgate.com/prune-overgrown-rhododendron-hurting-56701.html

My 50 yr old died last year after hard sub-zero freezes and dry winter...

DO NOT prune anything you want to see blooming... the blossoms have formed at the tips of branches already...

I'd wait till blossoms are done in spring.

Rule of thumb: Almost any deciduous tree can be pruned UP TO 1/3 of all growth. Whatever is done, consider the Shape of what remains, and allow a year or 2 for new growth to fill in the prunings.

Get a new saw blade (I assume you use a bow saw)... rhododendron are among the Hardest wood in North America.

Also, I found stress on a Rhododendron may appear in its growth and foliage two Years AFTER the stress occured... Keep yours heltered, watered (especially Before the ground freezes) and if needed, wrapped in burlap.

Janet... great source, and I find agreement with near everything it has to offer!

I think thisw will help!