To start, let’s get one thing straight: all azaleas are rhododendrons, but all rhododendrons are not azaleas.
How to Prune Rhododendrons and Evergreen Azaleas
By Robin Haglund
Scientifically, they all belong to the genus Rhododendron. From there, they break down thousands of species, varieties and cultivars. Fortunately, the same basic pruning principles apply to all of them. So, even if you aren’t sure which kind of rhodie was planted in your garden, perhaps generations ago, these tips should help you keep it healthy and blooming beautifully for years to come.
Rhododendrons can range in size from tiny miniatures like R. impeditum, which gets no bigger than about a foot tall and wide, to towering, bushy trees that create colorful spring canopies above our heads. Their leaves may be shiny or dull, green, grey or variegated, fuzzy beneath or bare, curled at the edges or flat. Plus, you’ll find a rhodie blossom in nearly every color of the rainbow. And, although we generally think of these plants as spring bloomers, some varieties like the ‘Christmas Cheer’ cultivar will bloom in the dead of winter. And those that bloom the earliest in the year will sometimes surprise us with a second bloom later in the fall. Plus, the adaptable evergreen rhodendron provides great year-round interest in just about any garden – just be sure to match your plant choice to your planting zone when buying your plants.Rhodies are fairly simple to prune. Although many can bounce back from a heavy cutting to the ground, it may take years to regrow. Instead, pruning a little bit each year is the ideal way to keep your rhodies and azaleas looking good all the time.
Take note: Rhododendrons will bloom even if you don’t deadhead them. Deadheading, or removing flower clusters after they have begun to fade, is really more of an aesthetic choice. Think about it: plants have flowers that bloom, are pollinated and become seedpods. In nature, nobody is out there cutting spent flowers off wild shrubs. And those plants bloom year after year in an attempt to replicate themselves by forming new seed, which it hopes will form new plants. The same is true in your own garden. If you do choose to deadhead, try to remove spent flower heads right after blooming and before the tender branching buds begin to grow, or you may find yourself breaking lots of new growth accidentally.
Ideally, rhodies and azaleas are pruned like small, woody trees. If your rhodie hasn’t been pruned in a while, you may find you have lots of small cuts to make. Once you do this first big clean up on your shrub, the work required in subsequent years should be much less. Although some would argue that evergreen azaleas can make a lovely sheared hedge, I will caution that if sheared incorrectly azalea hedges will not bloom. Ideally, these plants are pruned to their natural form rather than sheared into some arbitrary shape.
Before beginning to prune your rhodies, consider spreading a large tarp or old sheet under the shrub where you can drop all of your cuttings. This will allow you to work more quickly, and it will make cleaning up all the trimmings easy at the end of the day.
To begin -- at just about any time of year -- remove any dead material from the interior of the plant. Azaleas, in particular, are notorious for building up lots of dead twigs on their inside branches. This happens because the evergreen leaves shade the interior of the plant. When those interior leaves become so shaded that they are unable to photosynthesize, the plant lets them whither rather than continue to draw valuable assets from the rest of the plant. Clearing out this material will improve the look of the plant while also allowing more light and airflow into the interior of the plant, which helps keep down potential disease issues.
The next pruning steps are best performed as the rhodie is blooming or just after it has finished its primary bloom. If you prune just before the plant blooms, you risk removing that year’s flowers. If you prune several months after flowering, you risk removing the flower buds forming for the next year’s bloom.
Once you have removed the dead material, you should be able to see if the plant has any broken branches, branches rubbing against each other or branches growing in directions other than away from the trunk of the plant. These are the next to be removed. When cutting these branches out, be sure to remove the entire stem to the junction where it meets another stem, leaving the little raised ridge at this junction intact on the plant. Most cuts can be made with your bypass hand shears, but be sure to have a folding handsaw in your pocket for any larger branches. And, ideally, remove no more than one-third of the plant’s living branches in one year.
Once you have finished with the initial cleaning of the interior of your rhodie, the last thing to do is prune for shape. You may notice that when rhodies open new branch buds after flowering, they often send up several new branches at one time from below the flower. This can make for heavy, drooping shrubs. In these cases, consider removing one or two of the outermost branch extensions, leaving one or two in place. Always select the weakest or most oddly branched options for removal. And, with all cuts on rhodies, make sure to remove the entire shoot, leaving no stumpy growth behind.