For some reason I can't access rhodyman's site.
My Rhododendrons have buds, one is starting to bloom.
I usually apply an acid fertilizer each year, but I forget if now is the time to do it, or if I should wait until the end of May.
He suggests May, and no later than July.
In my naturally acidic soil, my own don't require fertilizer - they are top dressed with compost each Spring and that's been all they've needed.