It seems like I keep harping about the same old thing, must you need to prune your flowering shrubs just as soon as they are finished blooming. Forsythia, magnolia, azaleas and some early rhododendron have already bloomed and now is the only time of the year when they can be pruned without cutting off their flowers for next year. The way it works is like this: the winter cold weather sets the flower buds that bloom in the spring. After they bloom is the only time in which you have the opportunity to make and shape your plants to a smaller size. I know what happens...you wait until fall after your plant grows all summer and gets too big for your liking. Then you decide to prune it, cutting off all possibilities for flowers to appear in the spring. Remember this, your plants will grow after you prune them in the spring so get the job done now.
Pruning is real simple but you must be brave and confident that they will indeed grow back. Last year after the azaleas bloomed here at the greenhouse I instructed the girls in pruning them back. At first they only wanted to cut off the dead flowers and that was it. "No," I said, "you must cut back about one third of the plant." Well, needless to say, that was like cutting off ones arm. It seemed too drastic but we did it anyway and then all through the summer, with the help of plenty of water and fertilizer, the azaleas grew back into a perfect shape never to be cut back again until next year after they bloomed again.
We have already cut back our forsythias and magnolias and are ready for the azalea/rhododendrons to finish blooming so that we can cut them back. Our lilac bushes are in full bud and just about ready to bloom so we will wait on them to do their thing before pruning.
It is so obvious when not to cut back a plant that is budded and ready to bloom but when the blooming is over, there are always questions about the pruning process. You must pay attention to the simple details of what just finished blooming and then go prune that plant back, and don't wait. They sooner you cut them back, the more growing time they have before late summer and fall when the flowers set for next year.