The Rhododendron Collection at the University of Washington Arboretum
J. A. Witt, Assistant Director
Size of Collection:
Approximately 300 species and varieties, 165 named clones, and probably 200 unnamed hybrids, with a total of over 4,000 plants. These range in size from nearly prostrate R. prostratum to 18' tall R. discolor.
Location of Collections:
The main collection is in Rhododendron Glen, a valley facing predominantly west with an over story of old native trees. The species are found here for the most part, and are planted in series groups. Interspersed with the species are numerous hybrids including a large collection of Dexter hybrids sent to the Arboretum in 1938 and 1939. North of Rhododendron Glen there is a more or less continuous planting of both species and hybrids, which extends for about one-fourth mile and includes many plants of considerable size and age as well as some raised from seed since 1955, while to the west there is a bed planted with a number of hybrids of local origin. (Fig. 21)
Fig. 21. The University of Washington Arboretum. Looking down the
south bank of Rhododendron Glen.
E. F. Marten photo
The north end of this planting is another west facing valley, Loderi Valley, that contains our collection of Loderi hybrids and a large group of very handsome seedlings raised from them. Several of the more outstanding of these seedlings have been chosen for propagation, and one, 'Mrs. A. F. McEwan', has been named.
Other rhododendrons are planted in such places as the Japanese Garden, the Winter Garden, where some of the early spring flowering hybrids and species are kept, and in the lath-house which contains some of the rarer and smaller species unlikely to survive in the Arboretum proper.
Time of Flowering:
Flowering actually starts with R. mucronulatum in winter or early spring, continues with some of the earliest of the Fortunei series in late February or early March, reaches a climax in late April and early May with masses of species and hybrids in full flower from then until June when the blooming begins to taper off, finally ending the season with R. auriculatum in late July or early August.
During the Conference there should be a fine display of the 'Loderi' group in Loderi Valley. These plants, seedlings of rhododendron 'Loderi', are now about twenty years old and are mass planted beneath native firs and hemlocks in this sheltered valley. Despite the similarity among them of foliage and habit there is a striking difference in the flowers of this hybrid group. Many of the blooms resemble the parent plant, but the colors range from yellow-cream through pink blends, with some very striking whites and several with definite green eyes.
In Rhododendron Glen visitors will find a magnificent display of the Himalayan Rhododendron wardii group, plants about six feet tall and as much across, covered with soft yellow cuplike flowers, some with a splash of bright crimson in the throat. Below the R. wardii group is a bed devoted to members of the Fortunei series where one species or another will be found in flower from early March until late June. This magnificent collection contains some of the largest rhododendrons in the Arboretum, and one may expect to see R. houlstonii and R. orbiculare flowering during the first half of May.
In early May the south bank of Rhododendron Glen is a mass of pastel colors from the rhododendrons of the Triflorum series growing there. Predominant are the blues of Rhododendron augustinii, with white, soft pink, purple and pale yellow furnished by other species of this series.
Another area of interest to the rhododendron enthusiast is Azalea Way a broad grassy walk about 3/4 of a mile long bordered with rhododendrons of the Azalea series, both species and cultivars. From early May until late June one group of azaleas follows another in making this walk a "must" for any visitor to the Arboretum.