As we move through the end of May it becomes imperative that any pruning (think shaping and also about next year’s flower production) of spring flowering shrubs, like Rhododendrons, Azaleas, Lilacs, and Forsythias, needs to be done NOW. The rule is simple: “Prune after bloom”.
All plants that bloom before the end of May are blooming from flower buds that were produced the previous season. They are formed on what we often call “old wood”, “one year old wood” or simply last year’s growth. So early season bloomers like lilacs or Forsythia, and all spring blooming perennials like Candy Tuft, Rock Cress, and Winter Heather should be pruned once the flowers fade. If you wait and prune these spring bloomers in the fall or winter, you will cut off all the flower buds, and while the plant will be just fine, you won’t get any blooms which kind of defeats the whole purpose of growing them in the first place.
I guess I should interject at this point that not pruning your spring bloomers is not the end of the world. In the case of shrubs like Rhodies and Forsythia, they will just keep getting bigger and depending on where they are growing in the garden, that may be just fine. The problem arises when they get too big and you are forced to shear them, which in the case of a Forsythia, can end up looking incredibly hideous. Personally, I enjoy having a few sheared shrubs in my garden, but they are almost always a broadleaf evergreen like a Laurel or Japanese Holly, and I am not concerned about blooms. I use them in juxtaposition to informal and naturally shaped shrubs which do bloom and the combination is quite pleasing. Otherwise, creating what I like to call “green meatballs” out of shrubs like forsythia and rhodies (or ice cream cones out of barberries and nandinas) falls into the category of plant abuse in my opinion.
Most plants don’t need constant pruning. Lilacs for example, once they are established, should have only one third of the older stems removed every couple of years - this helps to stimulate the plant to produce new growth. That being said, if you never prune your lilac, it will still continue to bloom, but it may become a weedy mess due to all the suckers it tends to produce. At the minimum, at least keep the suckers thinned out and save a few for replacement wood.
Plants like forsythia can be managed best either by selectively removing older stems after they have bloomed or by whacking the whole bush down to about one foot tall. While this kind of drastic pruning will leave a temporary void in your landscape, it will result in vigorous growth that by the end of summer will fill up the spot with new stems that will bloom from their base all the way to their tips the following spring.
For more information on pruning spring and summer blooming shrubs like roses and the ever-confusing hydrangeas, check out our upcoming classes or go to the “Info Hub” on our Sunnyside Nursery website. Also, some of our growers, like Monrovia Nurseries, have wonderful consumer-oriented information that even a seasoned professional like myself finds useful. Just remember, while there is potential to foul up the bloom cycle of a shrub, you will rarely kill it or cause any permanent damage (other than making it look like hell and being in the dog house with your spouse). Everyone has to start somewhere and it is easier to get the hang of than you think, plus there are always horticulture experts to help you along the way, so give pruning a shot! Stay safe and keep on gardening.
