Help your favorite woody plants look their best, whatever the time of year, with this helpful manual.
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Rhododendrons make a beautiful addition to any landscape. Their evergreen foliage provides year-round interest and their spring flowers are simply spectacular, says Scott Hemler, a professional landscaper who manages the sprawling estate at Colonial Williamsburg. "The genus Rhododendron is a large group with many different plants within it," he explains. "Many are cultivars of Rhododendron catawbiense, such as the old 'ironclad' varieties like 'Boursault,' 'Nova Zembia,' and 'Roseum Elegans.'"

Best of all, they are typically easy to raise—so long as they are in the right spot—and have a long lifespan. "They grow best along the Pacific Northwest coast and the eastern United States, where several kinds are native to the Appalachian Mountains," says Hemler. "They are generally hardy in USDA zones four through eight, but hardiness can vary by species." As for how to keep these woody shrubs looking their best? Tackle their care on a season-by-season basis, he notes.

pink Rhododendrons and Picket Fence
Credit: dndavis / Getty Images

Spring

Rhododendrons traditionally put on their biggest show during the spring, when they burst into purple, white, pink, and red flowers. "Early spring is also a good time to plant them," explains Hemler. "A partly-sunny, north, or east-facing spot around your house with well-drained soil is ideal." These shrubs don't like hot afternoon sun, and can often thrive in the woods, under tall growing pines or deciduous trees in a gently sloped area. "Rhododendrons are not heavy feeders, but you can fertilize in the spring with a formula for acid-loving plants," he says.

Summer

After your plant finishes its bloom cycle for the year, it's time to get to work. Begin by carefully remove spent flowers and seed pods: "This helps the plant put its energy into growth and flower bud production for next year's bloom show," notes Hemler. Since rhododendrons don't require much pruning, you won't have to cut them back much; if some snipping is needed, you have a short window—after the final bloom period all the way up to bud production—to do so. "Usually, they are not pruned after July Fourth," he says, adding that rhododendrons produce their buds in the summer, which overwinter and then open the following spring. "The large buds are produced at the end of the branches and are easily noticed when they are fully formed."

Rhododendrons have shallow roots and don't like drought, so deep watering once or twice a week during this season is best. "They will let you know when they are dry by drooping," he explains. If you want to propagate your variety, get slicing in mid-summer. "Although they are not easy to root, cuttings taken in August and put in damp potting soil in the shade have the best chance of establishing," he explains, adding that this process can take months. "The newly-rooted cuttings can be overwintered in a shady cold place or in a cool greenhouse." It's a long haul, though: Plants will be ready for your garden after two to three years hardening off in a pot. As for summer pest control? "Rhododendrons are usually pest free, however, root rot can be a problem if the soil is not well drained," he says, adding that stem borers can bore into a branch stem causing it to die above the entry point. "To remediate this, cut out the dying branch above where this insect entered the stem, and destroy the infected branch."

Fall

Fall is another apt time to plant new varieties—or to apply pine bark mulch or pine needles to your existing plants. "Pine bark mulch and pine needles are a good choice of mulching material, as they do not mat down and get compacted like some other options," Hemler explains. "As they decompose, pine bark mulch and pine needles acidify the soil, which is great for rhododendrons. Continue to water in the fall if your plants are dry."

Winter

Since rhododendrons are very cold hardy, and usually do not need any winter protection, there is little to do during this time of the year. "Water them well, though, if it is particularly dry," Hemler says, adding that it's always a good idea to make sure any evergreen plant is well-watered ahead of a freeze. "Evergreen rhododendrons are a living thermometer! As the temperature falls below freezing, the leaves begin to droop and curl up, which is a natural response to the cold." The colder it gets, the tighter the leaves will curl up, giving you a good idea of what the weather is like outside your window. "When the temperature rises above freezing, the leaves will uncurl and go back to their normal position," he says.

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