Once you've been tempted to venture beyond the ubiquitous varieties available at garden centers, you'll find that rhododendrons can be fussy plants. The first step to success is choosing plants that are suited to your climate. By joining the local chapter of the American Rhododendron Society (ARS), “you'll end up talking to people who know which rhododendrons will grow and flourish in your area,” says Michael Martin Mills, former president of his ARS chapter. Most chapters include on their websites a list of less familiar plants known to do well in that specific locale, including the cultivar's essential stats: name, color, height after ten years, hardiness, and bloom time. These proven performers often turn up at the chapters' annual sales, held in midspring when the majority of plants are in bloom. A 20-inch plant might fetch $25 to $30, with more exceptional specimens—the kind you aren't likely to find at your local garden center—costing more.
Photo By: Axel Oehler. Laetum Flower, The Rhododendron Park and Botanic Garden
As for planting and cultivation, a rhododendron needs three things above all else: drainage, drainage, and drainage. “They actually like to grow on top of the landscape, as opposed to deep in the ground,” says Harold Sweetman. Rhododendrons also prefer acidic soil, which is why huge swaths of the alkaline Midwest don't even bother. Amending the soil with organic matter such as leaf mulch or fine bark will help both the acidity and drainage. To check the drainage, dig a 20-inch-deep hole and fill it with water. If the water disappears in four to six hours, you're good to go. Be sure to spread out the root system before planting. Mulch with compost, bark chips, or pine needles to prevent weeds, since hoeing can easily damage a rhododendron's surface roots.
Though they're not shade plants, many rhododendrons prefer partial coverage, especially those with large leaves. To work rhododendrons into your garden plan, think beyond the foundation bed. “This plant is for people who like to look at a variety of textures and forms in the garden,” says Laura Grant, executive director of the ARS. “You can design a dynamic tapestry just out of the rhododendron's leaves.” That will provide year-round visual interest, while choosing plants with staggered bloom times will guarantee several months or more of splendid color.
Rhododendrons make wonderful companions to other acid-loving plants and trees, such as ferns and flowering dogwoods. Many bulbs, like tulips, daffodils, and lily-of-the-valley, will bloom around the same time as a rhododendron without competing for water, nutrients, or space. If you've inherited a mature shrub on your property, space may be a problem. “I take a turn manning our chapter's exhibit every year at the Philadelphia Flower Show,” says Mills (March 6–13 this year), “and I can't tell you how many people come up to me and say, “What should we do? We can't see out our dining room window anymore.” Not to worry, he says, its shallow roots make for easy transplanting.