SPRING in the Pacific Northwest is a time of riotous garden color, thanks largely to that hardy plant whose scientific name - Rhododendron - means "rose tree." They come in virtually all sizes, from rock-garden miniatures to trees that loom over the tops of houses and in virtually every color of nature's palette.
In public and private gardens around Portland, Ore., and Seattle, Wash., hundreds of varieties now are putting on their annual spectacular display.
But with some 1,000 known species and many more hybrids, "rhodies" also are native to many other regions of the United States as well as parts of Asia, Europe, and the South Pacific. And given their beauty, and the relative ease with which they can be grown and hybridized, rhododendrons are becoming one of the most popular plants with hobby gardeners.
"Once you start, it's almost like an obsession," says Barbara Hall, executive director of the American Rhododendron Society. Mrs. Hall and her husband live in Gloucester, Va., where they've planted two acres of rhodies and azaleas (both of which belong to the genus Rhododendron). The Halls have more than 1,000 varieties on their property, and by late April and May when everything is blooming "the plants are just gorgeous," she says.
The American Rhododendron Society now includes 6,000 "rhodophiles" in 70 chapters (including groups in the Netherlands, Denmark, Scotland, and India), and their numbers continue to increase.
"In British Columbia, they're growing by leaps and bounds," says Hall. The organization's quarterly journal recently reported a new group forming in Estonia.
In Portland, Ore., the local chapter has no trouble drawing 100 people to its monthly meetings. "I don't know of any other group with that kind of vitality," says Linda McMahan, executive director of the Berry Botanic Garden here.
Located in the hills above Lewis and Clark College at the south edge of Portland, the Berry Botanic Garden has some 150 rhododendron species totaling 900 plants, spread over six acres (as well as collections of alpines, primulas, lilies, and native plants).
The garden was started in the 1930s by Rae Selling Berry, a tireless amateur gardener who was able to obtain specimens from expedition groups that had traveled to China and worked the garden herself well into her 90s.
When the Berry estate was being disposed of in the 1970s, a nonprofit group raised money to save what had become an internationally renowned species garden from development bulldozers.
Today, the garden staff makes use of a seed exchange with other gardens and a seed bank (an Amana freezer in what was the Berry family's laundry room) to help preserve species that in their native habitat are becoming endangered. In China, for example, very large rhododendron trees are often cut down for firewood.
"There are quite a few species [that] if they were to go would be irreplacable," says garden manager Will Simonds. "Some are found in only four or five other places in the United States. Passing them around to as many people as possible is a way to keep the species going."
Since rhododendrons form new hybrids so easily, Mr. Simonds and his staff must take special measures to obtain original species seeds.
This process involves tying a sheer material (usually panty hose) over flowers that have been pollinated by hand in the spring from the same plant or from one of the same species. In the fall, this simple form of protecrtion against cross-pollination by bees or hummingbirds is removed, and the seeds are guaranteed to be of the proper species.
Several hours north of Portland in Federal Way, Wash., the Rhododendron Species Botanical Garden displays nearly 2,000 different varieties of more than 500 species found in the wild from the arctic to the tropics - from an inch high to 100 feet tall. The garden is located on 24 acres at the corporate headquarters of the Weyerhaeuser Corporation.
In nearby Olympia, the Washington State capital, the Briggs Nursery is the largest producer of rhododendrons in the world. Much of the collection comes from a tissue culture laboratory that produces millions of plants a year, many for international export.
GROWING plants from tissue culture, says Hall of the American Rhododendron Society, "will relieve some of the stress on the wild stands, since there's no need to dig them up."
Hall adds, however, that "the problem now is not so much people digging them up in the woods but urban development and the loss of habitat."
One of the rarest Ericaceous (heath family) shrubs in the northwestern United States is the Kalmiopsis, found in the mountains of southern Oregon. Believed to be a prehistoric parent of all rhododendrons and azaleas, it is grown from cuttings by Baldassare Mineo, owner of the Siskiyou Rare Plant Nursery in Medford, Ore.
For garden hobbyists, one of the main satisfactions comes from experimenting with new hybrid varieties. "It's like children - you never know what you're going to get," says Hall "You may get something entirely new, or it may turn out not to be as good as either of the parents."
Simonds of the Berry Botanic Garden ticks off the characteristics that make rhododendrons so popular: hardiness, fairly low maintenance, "showy," and easy to hybridize.
"They're really not that difficult to grow if you have the right situation," he says. "And they certainly have a variety to suit just about everybody."
For further information about rhododendrons, write:
* The American Rhododendron Society, P.O. Box 1380, Gloucester, VA 23061
* Siskiyou Rare Plant Nursery, 2825 Cummings Road, Medford, OR 97501
* The Rhododendron Species Foundation, P.O. Box 3798, Federal Way, WA 98063
* The Berry Botanic Garden, 11505 SW Summerville Ave., Portland, OR 97219
* Briggs Nursery, Olympia, WA 98501