By Katie Lutz

WSU Master Gardener

As I was pruning one of our rhododendrons awhile back and brushing off a steady rain of disturbed spiders as I did my work, I thought to myself, “What exactly makes the rhododendron so popular here in the Pacific Northwest? What do I really know about them?”

To start with, over 1,000 species are currently classified under the genus Rhododendron, which also includes the equally enjoyed azaleas. They are native to much of the world, although a majority are native to locations in Asia. Rhododendrons can be found ranging from the temperate regions of North America and Asia to more tropical areas of Southeast Asia and Australia. However, it is interesting to note that no native species originate in Africa or South America.

In addition to their huge geographic range, rhododendrons can be found in a wide variety of habitats. Wild species have been discovered growing in alpine regions (up to 19,000 feet in elevation), diverse types of woodlands, rainforests and tropical jungles. Some — like our state flower, the Pacific rhododendron (R. macrophyllum) — even sprout quickly after being disturbed by fire or from being cut or damaged. Rhododendrons grow best, though, in temperate climates with a decent amount of rainfall and acidic soils, which is why the Pacific Northwest — and parts of the U.K. — make ideal habitat for these plants to grow.

In terms of growth habits, rhododendrons aren’t limited to the midsized shrubs that we know and love. Alpine forms may only grow a few inches tall and act as a groundcover. Other species can reach heights of 100 feet and more closely resemble a tree.

The leaves, flowers, and bark also display a large amount of diversity. For example, flower colors include shades of red, yellow, purple and orange. Even more astonishing, single leaves of one species of wild rhododendron (R. sinogrande) can grow as big as 3 feet.

Our love affair with rhododendrons didn’t stop at propagating the many existing wild species. Creative gardeners have been trying to “improve” rhododendrons by creating hybrids between different species. This can be done for a variety of reasons, such as trying to create a more frost- or heat-tolerant plant, larger flowers, and/or new flower colors.

The downside of creating all these hybrids is that it can make correct species identification a little difficult at times. This is why when you take a trip to the nursery to purchase a rhododendron, the hybrids that are for sale are usually only able to be listed as Rhododendron “Variety Name.” Most rhododendrons that are grown commercially are hybrids, and that’s mostly what you’ll find growing in gardens around the Pacific Northwest. Since rhododendrons hybridize so easily, over 10,000 hybrids have been registered internationally. To further confuse everybody, there are also over 10,000 azalea hybrids registered.

If you want to get to know some of the wild species of rhododendron, we have a great resource in our backyard. The Rhododendron Species Foundation and Botanical Garden is a nonprofit located in Federal Way dedicated “to conservation, research, acquisition, evaluation, cultivation, public display, and distribution of Rhododendron species.” It features over 700 of the 1,000 known species of wild rhododendron.

Even more amazing is the fact that the 22-acre property has something in bloom from January all the way through October. The Botanical Garden also features a nursery where you can purchase some of these hard-to-find wild species, hybrids and good companion plants. If you want to learn even more about rhododendrons or plan a visit, just check out rhodygarden.org/cms.

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Interested in joining the WSU Master Gardener Program? Applications for the Class of 2018 are available now at pnwmg.org.

Katie Lutz, of Hoquiam, joined the WSU Master Gardener Program in 2016 and is fortunately not bothered by spiders.

“Blaney’s blue” rhododendron offers some bright contrast to a Japanese maple.