Penny-wise Planting, Part 4 - A Primer on Pruning Azaleas

Thursday, March 19, 2009

The ubiquitous azalea bush often outgrows its allotted space. Some hybrids can reach eight feet high or more and as much in width after a few years. Fortunately, this is a shrub that is easy to prune, as Barbara Bullock can demonstrate.

She is the curator of the azalea (and rhododendron) collection at the U.S. National Arboretum and spends much of her winter renovating overgrown shrubs. Many were planted 60 years ago and have grown 12 feet tall, with upright and arching stems.

Bullock uses a hand saw to remove some of thickest stems and prunes others down to three or four feet above the ground. They are removed neatly where they connect to another branch. She favors a three-cut method, first slicing through a stem a couple of feet above the final cut. She then removes the stub by cutting halfway through the stem and finishes by sawing it on the other side. This prevents the wood from ripping and leaves a clean wound that will heal quickly.

You can cut back an overgrown azalea to just a few inches above the ground, and by watering and feeding it, you will get vigorous rejuvenation, but it will take two or three years to look attractive again.

In an arboretum garden with less shade, Bullock tackles younger azaleas that have grown too tall and wide, bringing them down from more than six feet to under five. By narrowing them, she gets them to read as individual specimens. But the key is to prune in a way that keeps the azalea's natural layered effect. "My goal," she said, snipping away with hand pruners, "is to make it look like I haven't done anything."

Drought-stressed azaleas develop a serious disease called botryosphaeria; look for dead and dying foliage on one side of a stem. The affected branch will have a brown stain in the wood, so cut low to a point where the pith looks white and clean.

Azalea pruning should be done now, before spring growth. Obviously, you are removing next month's flower buds, but that's okay. In addition, azaleas, even established ones, can be moved to a more suitable location. Oh, and there is a special place in hell for people who shape azaleas into cubes or globes.

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