Rhododendron Revisited

Rhododendron Revisited

August 15, 2012
Photo by: Rob Cardillo

Also related: Scenic Route and Grow Your Own Rhododendrons

Picture the absolute antithesis of your mother's foundation garden, and it might look something like the Milke Danda region of Nepal. Here, clapboard siding is replaced by the Himalayas' jagged, soaring peaks. Instead of wind chimes on the front porch, there's the flutter of prayer flags. And what are garden gnomes compared with the ancient carved Buddhas of the mystical Tibetan mountain people? Still, despite being worlds apart, this forested ridge in eastern Nepal and your mom's familiar front beds likely have one thing in common: the rhododendron.

The rhododendron—from the Greek rhodon (rose) and dendron (tree)—is thought to have evolved on the Asian continent more than 50 million years ago. Indeed, some Bible scholars contend that the dove returning to Noah's ark must have been carrying a rhododendron sprig, not an olive branch. It's a woody descendant of the magnolia whose habit ranges from crawling to shrubby to treelike. A member of the acid-loving ericaceae family, the rhododendron's cousins include heaths and heathers, huckleberries and blueberries.

The vast majority of wild rhododendron species still hail from Asia, including Nepal, where organized tours of “rhodies” trek for weeks each spring, like disciples of a religious order, to gaze upon rhododendron-filled woods. The cloud forest of Milke Danda is home to some 20 species that light up the hills every April with colorful flower clusters known as trusses.

Hard-core aficionados follow their devotion to the “king of shrubs” beyond guided treks to Indian Jones—like adventures: one such plant hunter, Steve Hootman, executive director of the Rhododendron Species Foundation & Botanical Garden in Federal Way, Washington, has pursued the plant throughout India and China since 1995.

“It's the thrill of the chase,” Hootman says. “You're climbing cliffs and crossing gorges on bamboo-cane bridges just to get to that one territory that hasn't been explored yet.” Harold Sweetman, executive director of the Jenkins Arboretum & Gardens in Devon, Pennsylvania, recalls an ecstatic moment in Arunachal Pradesh, a northeast Indian state wedged between Bhutan and Burma. “In a single mountain ascent we counted 50 species,” he says, ranging from ‘Exasperatum,’ with its brick-red blooms and rounded foliage, to ‘Glischrum,’ whose woolly leaves were unlike any he'd ever seen. “It fills you with awe to see that kind of diversity and adaptability.”

Really? Rapture from that leggy, front-yard behemoth where Wiffle balls went to die? As enchanting as rhododendrons may be in the wild, in captivity here in the United States they've been reduced to a default foundation filler, a supporting act for the flowering annuals and perennials we actually care about. The demotion is a classic case of the fittest surviving, with nurseries playing the role Darwin ascribed to Mother Nature.

“The big growers found a few plants in the 1970s that propagate well and are impossible to kill,” explains Hootman, “and that's what they've been growing ever since.” He estimates that 90 percent of all the rhododendrons sold in the U.S. are the same ten or so ironclads—primarily large-leafed cultivars that can shrug off the cold and heat alike, thanks to resilient root systems.

George Woodard, a hybridizer who has been crossbreeding rhododendron on a 100-acre private estate in Old Westbury, New York, for three decades, shares Hootman's view, but laces it with deep disdain. “Stick them in a pot, jam them with any commercial fertilizer, and they'll jump into plants,” he says as he surveys his 1.5-acre seedling nursery, where about 3,000 new plants are slowly coming to fruition. “Don't even talk to me about them.”

Some Bible scholars contend that the dove returning to Noah's ark must have been carrying a rhododendron sprig, not an olive branch

Market-saturating stalwarts include ‘Scintillation,’ a broad-branched shrub with sweet pink flowers that you might recognize from your bank's parking lot; ‘Cunningham's White,’ whose brown-flecked blooms and dark evergreen leaves were introduced in 1830; and the heavy-blooming group of home center regulars known as ‘PJM,’ whose reddish-purple trusses spring from glossy, elliptical leaves. True fans don't suffer these hybrids gladly. “When I mention the name ‘Roseum Elegans,’ most of our members start gagging,” says Jim Fry, president of the New York Chapter of the American Rhododendron Society (ARS), referring to the lilac-bloomed shrub known for ball-shaped trusses that average 20 flowers each and sold at big-box stores and nurseries from Monterey to Montauk. “It's sort of like the Model T of rhododendrons.”

Familiarity has bred indifference, if not outright contempt. “When I tell novice gardeners I'm into crossing rhodies,” says Woodard, “they give me this look like, ‘Who would want to mess with those boring things?’” But to rule out the entire genus based on the overused few is like avoiding fine restaurants because you don't care for fast food.

Diversity in nature elicits devotion in man. We would never have so many bird-watchers if there weren't so many birds, and so it is that the rhododendron has earned its devout following. “It's one of those plants, like hostas and daylilies and roses, that people get really into and collect lots of and form societies around,” says Michael Martin Mills, board member and former president of the Greater Philadelphia chapter of the ARS.

The passion is global, though with pockets of extremism. Germany has some of the world's largest growers, namely the Hachmann Nursery in Barmstedt, north of Hamburg. “The Germans have gotten very good at engineering compact, dwarflike plants that are just covered with huge, beautiful flowers,” says Woodard. In Denmark, private gardeners take advantage of the mild climate to cultivate their own ravishing collections. And across the North Sea, English and Scottish gardeners continue to exhibit the rabid devotion that yielded the British Rhododendron Society in the early 20th century.

The U.S., however, is home to the world's largest collection of rhododendrons. The Rhododendron Species Foundation Botanical Garden, which covers 22 acres in a conifer forest just south of Seattle, boasts more than 600 of the 1,000-plus identified species. All major subspecies of the genus are represented, starting with the most common, the elepidotes (meaning leaves without scales). These plants typically feature large foliage that is sometimes covered with fuzzy, feltlike indumentum, and iridescent flowers that tend to bloom like clockwork in or around May. If you've ever given or received a rhododendron for Mother's Day, chances are it was an elepidote. Then there are the lesser-known lepidotes (meaning leaves with scales), which tend to be more compact, often standing just three feet tall after ten years, sometimes with variegated foliage that is fragrant when crushed. Lepidotes typically tolerate more sun than elepidotes do, and some flower earlier or later, from January all the way to June.

The vireya is the rhododendron's tropical subgenera, native to such hot spots as New Guinea, Borneo, and Hawaii. A majority of the 300 known vireya are epiphytic, meaning they live on trees, rocks, or other objects, rather than in the soil.

The final two subgenera of the rhododendron are azaleas—one evergreen, the other deciduous. Given their own diversity—the best-known reference book, Fred C. Galle's Azaleas (Timber Press, 1985) describes more than 6,000 varieties—azaleas are often mistaken for a separate class of plant. The easiest way to tell azaleas apart from the rest of the genus is by their hairy leaves and the fact that blooms have five stamens compared with the ten stamens on most other rhododendrons.

Wandering the Rhododendron Species Foundation is like traversing the Himalayan crescent in a single afternoon. Here is R. forrestii, a prostrate, creeping charmer from Tibet with tiny leaves and bell-shaped flowers. Over there is R. sinogrande, which can top 50 feet in the wilds of India and has the largest leaves of any rhododendron. R. luteum is an azalea with deep yellow flowers that give way to red fall foliage, and its strong, sweet scent, described by one aficionado as “fruit cocktail,” has been known to travel for up to half a mile. The foundation's new 5,000-square-foot conservatory, meanwhile, affords a peek into the equatorial jungle, verdant with vireya and other tropical plants.

Nature's rhododendron is an endless bounty. That's why some collectors, most notably many Danes, content themselves only with the species. But other enthusiasts, the hybridizers, play a direct role in the act of creation and have added thousands of names to an already sprawling genus.

The science of hybridizing is simple enough. “You're basically taking the pollen from one plant and putting it on the stigma of another,” says Woodard, who fondly describes most hybridizers, himself included, as “amateur backyard gardeners.” One way that breeders make exact clones of prized plants is through grafting, a technique preferred and perfected by the Germans in which one plant is merged onto the rootstock of another.

Hybridizing calls for patience, since it might take five years for a seedling to mature and flower, revealing the true nature of the cross, which may or may not satisfy its creator. “Very few people get the right plant with the first cross,” says Woodard. “I've been doing this for 30 years and I'm just starting to see some of the effects I want.” He does have two successful cultivars to his credit: ‘Diana Marguerite’ and ‘Kristi Lynn.’

In the U.S., many of Woodard's top colleagues are huddled in the Pacific Northwest, where the damp, mild climate is perfect for raising rhododendrons. Harold Greer of Eugene, Oregon, was something of a child prodigy in the field. In 1961, at the age of 16, Greer created ‘Trude Webster,’ a pastel-pink rhododendron that won the American Rhododendron Society's first Superior Plant Award, in 1971. A year later, he opened Greer Gardens, a 14-acre facility that serves local gardeners and also takes mail-order requests from around the world; his book, Greer's Guidebook to Available Rhododendrons (Offshoot Publications, 1982), is considered required reading for any fan. Greer says he now does less hybridizing but still walks the nursery grounds most days, dispensing wisdom and listening for it, too. “There's always something new to discover,” he says of his beloved plant. Another well-respected hybridizer is Jim Barlup of Bellevue, Washington, who has been crossing tough, cold-hardy East Coast rhododendrons for 15 years with the more vibrant blooms that thrive in his corner of the country. Barlup's efforts underscore the challenge faced by rhododendrons in colder climes, especially the Northeast.

The list of remarkable rhododendrons goes on, and each spring brings hope of a breakout hyrbid with never-before-seen habit or hue.

“We often envy people out West because they can grow things we can't,” says Philadelphia's Michael Martin Mills. “A lot of Asian species and their hybrids can't survive our cold winters.” Barlup hopes that two of his more recent creations, ‘Copper Dust’ and ‘Saralynn,’ will prove hardy to at least −10°F. These and other hybrids could end up benefiting gardeners in the West as well. “Plants on the East Coast have root systems that have evolved to handle hot soil,” Barlup says. “I'm hoping the root system inherited from these plants will result in a hybrid that can survive a hot summer on either coast.”

Temperature hardiness is one thing, but when it comes to pushing the limits of breeding, hybridizers tend to focus on color, namely coming up with a vibrant yellow that will stand up to weather extremes. “With a lot of garden plants, there's one color that's absent or almost absent,” says Mills. “There are no blue roses, for example, or red tall bearded irises. To the extent that yellow rhododendrons have been developed, none are robust enough to make really good garden varieties on the damp East Coast.” It's not for lack of trying. There's the pale-yellow ‘Hong Kong’ hybrid that Mills managed to keep alive for 17 years. “But it needed more drainage than you would have thought possible,” he says. ‘Capi-strano,’ a truer yellow bloomer developed by the same breeder, the late David G. Leach—who was once commended for his efforts to diversify the genus in “the somewhat unfavorable climate of western Pennsylvania”—had a lot of Zone 5 and 6 folks excited, but it doesn't seem to be standing the test of time. “The response I hear most is, ‘Oh, yeah, I've killed four of those,’” says Mills.

A color-saturated yellow rhododendron may simply be out of reach for East Coast growers. But rhododendron hybridizing is a religion with more than one holy grail. Case in point: the “species look,” which Jenkins Arboretum's Sweetman dubs the future of hybridizing. “You're combining the hybrid vigor with the diverse foliage, texture, and color of wild species,” he says.

The species look is noticeably smaller than the bulked-up, cabbage-head-truss hybrids of recent decades, reflecting the trend toward smaller gardens. “In the past, it was all about getting the biggest, showiest flower,” says Hootman. “Now it's all about dwarfing things down.” Downsizing has been made easier by one particular species, R. yakushimanum, named after the island in southern Japan where it grows in high, windswept elevations. Though an elepidote, the yak (or yaku), as it's known, is compact with beautiful blooms, distinctive indumentum, and tolerance to both cold and heat. The most commonly used parent in hybridizing for the past few decades, yaks are passing down their fine features to the latest generation of rhododendron.

“It used to be that everything would be six feet and taller after ten years,” says Mills. “Nowadays, you can even find elepidotes that will be no more than three feet tall in that time.” That includes ‘Ken Janeck,’ with its compact truss of pink-flushed flowers, and Cinnamon Bear, whose thick indumentum starts silver before turning a pleasant spicy brown.

The list of remarkable rhododendrons goes on, and each spring brings hope of a breakout hybrid with never-before-seen habit or hue. Most of the general public will miss these new marvels, seeing instead the same old ironclads. For true devotees, that may be just as well. “It used to be that not everyone could grow a rhododendron, so those who could tended to be a little snobby about it,” says Fry. “I often wonder if instead of opening up our chapters, we shouldn't go back to being more snobby. That might bring some of the appeal back.” Either way, on a craggy hilltop high in the Himalayas, a forest of rhododendron will soon explode in bloom, indifferent to the whims of man.

Daniel DiClerico is a New York-based writer who lost many a Wiffle ball during an otherwise idyllic suburban New Jersey childhood.


Cinnamon Bear
Photo By: Rob Cardillo.

'Cinnamon Bear'

Flower: White bell-shaped blooms, about 20 per truss.
Habit: Compact. 
Height after ten years: two feet.  
Leaves: New growth has white cast; at m aturity, a heavy cinnamon-brown indumentum.  Hardy to 0°F.

Roseum Elegans
Photo by: Rob Cardillo.

'Roseum Elegans'

Flower: Funnel-shaped and lavender pink with up to 20 blooms per truss.  
Habit: Dense and spreading.
Height after ten years: six feet.  
Leaves: Dark olive green and rounded, with cupped edges.  Hardy to -25°F.

Princess Elizabeth
Photo By: Rob Cardillo.

'Princess Elizabeth'

Flower: Eye-catching deep crimson blooms that turn paler at the base.  Forms tall conical trusses. 
Habit: Upright and taller than it is wide. 
Height after ten years: five feet.
Leaves: dark matte green.  Hardy to -15°F. 

Berg's Hardy Form
Photo By: Rob Cardillo.

'Berg's Hardy Form'

Flower: Vibrant Dark shade of blue that appears in clusters of three and four. 
Habit: Upright and compact. 
Height after ten years: four feet.
Leaves: small (this is a lepidote) and dark green.  Hardy to -10°F.

Ken Janeck
Photo By: Rob Cardillo.

'Ken Janeck'

Flower: Deep pink funnel-shaped blooms form on a large truss.  
Habit: Compact and mounding.
Height after ten years: three feet.  
Leaves: curved dark green with striking toast-colored indumentum.  Hardy to -15°F.


This article was first published in Garden Design March 2011