Stewartia malacodendron blooming in the Arboretum in July.
BY RAY LARSON
Each year brings change to the gardens at both the Washington Park Arboretum and Center for Urban Horticulture (CUH) as we continue to add new plants for all to enjoy. As the collections age and mature, it is important to introduce new species and varieties—as well as younger examples of existing collections—so the gardens can stay resilient and better equipped to weather climate change, storm events, and disease pressures.
Following are highlights of some of the new plant additions from 2025 that will further our conservation and educational mission, as well as provide value for wildlife and inspiration for visitors. Your continuing support makes the care and maintenance of all the collections possible and helps ensure that our new plantings continue to demonstrate the beauty and benefit of a diverse, educational collection of plants from around the world.
Azalea Way: Dogwoods
Thanks to generous funding from Arboretum Foundation Unit 26, we were able to plant 16 new trees along Azalea Way. I’ve long wanted to add more trees that reinforce the original, historic Olmsted design of the promenade, which—in addition to azaleas—showcases flowering cherries, dogwoods and magnolias.
With many of the original dogwood plantings (primarily of flowering dogwood, Cornus florida) succumbing to the fungal disease anthracnose over the last 50 years, and just a few clusters of magnolias along the entire three-quarter-mile length of the trail, new plantings are needed to sustain the essential character and design intent of this iconic Arboretum feature.
A new Starlight® dogwood in bloom on Azalea Way in May.
We planted disease-resistant dogwoods along the middle and northern sections of Azalea Way. Of the seven specimens planted, four were Starlight® dogwood (Cornus × elwin-nortonii ‘KN4-43’), a hybrid between our native but disease-prone Pacific dogwood (Cornus nutallii) and the Asian Kousa dogwood (Cornus kousa). We have planted several specimens of Starlight® in recent years in different parts of the Arboretum, and they have performed well.
Growing to 30 feet tall and 23 feet wide, the hybrid combines the disease resistance of the Kousa parent with the large bloom size and rounded bracts (modified leaves that surround the flowers) of our native tree. We also planted three examples of Cornus kousa var. chinensis, a durable variety of the Kousa dogwood with dependably good flower production and fall color. A well-behaved tree, it grows up to 25 feet tall by 20 feet wide. The showy, white flower bracts are consistently abundant each May, look good for several weeks before fading, and are followed by red, strawberry-like fruits in late summer and fall. Autumn colors are in lovely shades of orange and red. I think it’s one of the finest small tree species for any garden.
Azalea Way: Magnolias
We added a few magnolias, including two cultivars (cultivated varieties) new to the collection. Along the lilac hillside, we planted a large specimen of Magnolia Honey Tulip™ (‘JURmag5’), a hybrid from famed New Zealand growers Felix and Mark Jury that offers large, creamy-yellow blooms on an upright, relatively small tree. The showy, spring flowers are goblet-shaped and grow up to six inches wide. Over time, the tree only reaches 15 feet tall with a narrow spread of six to eight feet.
Another selection with yellow flowers, Magnolia ‘Gold Star’, was planted at the south end of Azalea Way, close to the intersection with the Arboretum Loop Trail. Bred from selections of the eastern U.S. cucumber tree (Magnolia acuminata) and the star magnolia (M. stellata) from Japan, it produces star-shaped, creamy-yellow flowers with narrow petals. A larger grower, it will eventually reach 25 feet tall by 20 feet wide.
A new Magnolia Honey Tulip™ blooming on Azalea Way in spring.
Just north of the Rhododendron Hybrid Garden, we planted a young selection of Japanese bigleaf magnolia (Magnolia obovata) near an older specimen that has been in decline in recent years. Uncommon in gardens, this species features large, oval leaves and fragrant, white early-spring blooms.
Azalea Way: Flowering Cherries
Rounding out the new Azalea Way trees are three different cherry cultivars and one cherry species. At the north end of the promenade, we added two Japanese alpine cherries (Prunus nipponica ssp. kurlinesis). This is the northern subspecies of the tree—native to Japan, the Kuriles and Sakhalin—and it produces larger flowers and a smaller habit than the straight species. Soft-pink and white blossoms appear in abundance in April. The tree should grow to between 10 and 12 feet tall, maintaining an upright form.
Farther south along Azalea Way, west of the Witt Winter Garden, we added Prunus × yedoensis ‘Akebono’. This is a pink-flowering selection of the iconic Yoshino cherry, several mature specimens of which are growing on Azalea Way—including in the Centennial Summer Garden. One example was planted here to add some contrast to the white-flowering cherry cultivars to the south.
Just south of Azalea Way Pond, we added two cultivars that are new to the Arboretum, both of which promise good disease resistance and abundant blooms. The first is a weeping selection, Prunus ‘Snofozam’, with the trade name Snow Fountains®. Most of our older weeping cherry varieties have been hard hit by disease over the last 50 years, so we were eager to try this selection. A small tree, it only grows up to 12 feet high and wide. Fragrant, white blooms are produced in early spring, while the fall leaf color comes in shades of gold and orange.
A new Prunus Snow Fountains® weeping cherry planted near Azalea Way Pond.
Magnolia Collection
In the main Magnolia Collection area, we planted three new magnolias to add some smaller-growing specimens to an already expansive collection. These include two examples of lily magnolia (Magnolia liliiflora), both grown from cuttings from a tree on Azalea Way. Native to southwestern China, the species grows as a large shrub or small tree, ranging from eight to 12 feet high. It produces upright, pointed flowers in early May, with petals that are purplish-pink on the outside and white inside.
We also planted a specimen of Oyama magnolia (Magnolia sieboldii), grown from seed collected in the wild. Native to Japan, China and Korea, it is one of my favorite species, forming a small deciduous tree up to 15 feet high with a vase-shaped habit. Its nodding, white flowers open from egg-shaped buds in mid-May and display dark-red filaments at their center. Cucumber-shaped fruits follow later in the season and mature to a pinkish-red color. We haven’t had a specimen in the main collection for a while, and this new one will help fill the bloom gap between the early-season magnolias and the evergreen species that bloom in June and July.
Stewartias and Silk Tree
In the upper part of Rhododendron Glen, we added three examples of the infrequently encountered Stewartia malacodendron. This species is native to the U.S. Southeast, where it forms a small understory tree. While it doesn’t have the exquisitely peeling bark of Stewartia pseudocamellia or Stewartia monadelpha, it offers beautiful white summer blooms.
Lily magnolia blooming in the Arboretum in early May.
The large, two to three-inch-wide flowers feature purple filaments and blue anthers—a unique and lovely attribute. Young shoots are downy, and this—combined with the plant’s soft, camellia-like leaves and flowers—has given rise to the common name of “silky camellia.” Since the species is hard to propagate and grows relatively slowly, I have been waiting to plant these specimens out for some time, having patiently watched them for many years in the nursery.
In the Legume Family Collection along Arboretum Drive, just south of the Sequoia Grove, we planted a young specimen of Persian silk tree (Albizia julibrissin). Commonly seen in gardens, it has been absent from the Arboretum for well over a decade. With large, fern-like leaves on broadly spreading or arching branches, it can reach 30 to 40 feet high. The stunning, late-summer flowers are bright pink, fluffy and pin-cushion like, and they remain attractive over many weeks. The tree has no fall color to speak of, but few species rival its late-season flowering show. Our new specimen should do well in its open, sunny spot.
Lower Rhododendron Glen Pathway
Thanks to a generous grant from the Seattle Garden Club, we were able to install irrigation in two additional areas adjacent to the lower section of Rhododendron Glen that was restored in 2023. This has allowed us to trial unusual rhododendron species and woodland companions from climate regions with summer rain. Some of these plants are new to cultivation or untested in our climate. The Rhododendron Species Botanical Garden, Dan Hinkley, and Far Reaches Farm all generously donated plant species that we can now effectively assess in the ground.
Along the accessible path that was added to the lower Glen in the 2023 project, close to the new bench and overlook, we planted two low-growing, yellow-flowered rhody species with contrasting habits, both of them new to the Arboretum collection and uncommon in cultivation. One is Rhododendron valentinioides, a species that Far Reaches Farm collected near the border of China (Yunnan Province) and North Vietnam. It bears deeply-veined, glossy-green leaves with fuzzy margins. The smooth, ornamental bark peels in shades of cinnamon. Worth growing for the foliage alone, it also features dark-yellow flowers that bloom in early spring. Considered a dwarf species, it may only reach up to five feet high over time.
Our new Rhododendron semnoides. (INSET: The species in bloom; Photo: John Anderson, treesandshrubsonline.org)
Planting of the area begun in late fall, 2025. New to the Arboretum collection is Rhododendron jingangshanicum, a large-leaf rhododendron with long, large, wavy-edged leaves. Closely related to the more commonly seen R. calophytum, it offers shinier leaf surfaces and a brighter, pink-purple flower coloring. We expect the species will grow between 10 and 12 feet tall in cultivation. The plant is threatened in its limited home range of Mount Jinggangshan in Jiangxi, China, and so joins the Arboretum’s Conservation Collection.
Another big-leaf addition new to our collection is the Himalayan rhododendron (Rhododendron semnoides), native to southeastern Tibet and northwestern Yunnan Province, China. A large grower, reaching up to 25 feet tall in the wild, it produces dense trusses of rose-flushed-white, bell-shaped flowers in spring. The undersides of its nine-inch-long leaves are covered in two-layered indumentum (hairs), while the upper leaf surfaces are glossy, with attractive venation.
West of the maple snag, we planted a conifer with unique and attractive foliage: Fujian cypress (Fokienia hodginsii). Native to southeastern China, northern Vietnam and Laos, it has sometimes been considered a type of false cypress (Chamaecyparis), but its scaly leaves are larger and have flattened shoots. In the wild, where it’s vulnerable to extinction, it can reach up to 50 feet tall; but in cultivation it tends to be more shrub-like in habit.
Center for Urban Horticulture
Last winter, we began a major renovation of the large bed at the west side of the Elisabeth Miller Library at the CUH. This area had been greatly impacted by the 2004–05 reconstruction of Merrill Hall (following the 2001 arson incident), which caused a lot of soil compaction. In the immediate years after the building opened, only a few tree plantings took place. Irrigation was limited to a narrow strip of ground adjacent to the large trellis covering the west side of the library.
Our new Fujian cypress in lower Rhododendron Glen.
For much of the first decade after construction, the site contained simple plantings of Himalayan white birch (Betula utilis var. jacquemontii), Amur maple (Acer ginnala), some roses and twig dogwoods, and a few other random shrubs and perennials. But the site receives bright sun for much of a day, so it was calling out for more cohesion, year-round interest, and diversity.
In 2016, we renovated the westernmost, sunniest part of the bed with new plantings of several types of manzanita (Arctostaphylos species and cultivars) and other sun-loving shrubs, such as escallonia, bush anemone (Carpenteria californica), and mountain pepper (Tasmannia lanceolata), as well as amenity plantings of grasses and groundcovers.
The renovation was mostly successful. However, the birches had started to fail due to the effects of the bronze birch borer, and the amur maples had become increasingly ungainly and oversized next to the building. I had long wanted to showcase more of the Arboretum’s historic horticultural introductions at CUH, and this spot seemed a perfect place to do that—as well as to highlight some more unusual but garden-worthy plants in a prominent setting.
The renovated planting bed by the Miller Library, with Magnolia ‘Wada’s Memory’ in the middle ground.
As a first step, we improved the soil. Digging out the largest of the old tree roots actually helped break up the underlying soil and relieve compaction. Then we spread 25 yards of a well-draining soil mix and used donor funding to add irrigation lines with water-efficient heads. By March 2025, we were ready to begin planting.
We acquired a nine-foot-tall specimen of Magnolia ‘Wada’s Memory’ and planted it on the north side of the bed, where it could easily be viewed and admired. Introduced by the Arboretum in 1958, this stunning hybrid of two Japanese species (Magnolia kobus and M. salicifolia) remains one of the best white-flowering, small-to-medium magnolias for any landscape. It produces abundant, large, fragrant blossoms in mid-April before the leaves emerge. Ultimately reaching up to 35 feet high and 20 feet wide over several decades, it combines a dense habit with a slender, pyramidal form.
Closer to the library, we added a specimen of another Arboretum introduction, Nothofagus antarctica ‘Puget Pillar’. This selection of the deciduous Antarctic beech from Chile is significantly narrower than the straight species, due to its upright branching pattern. Its tiny, oval-shaped leaves have crinkly margins. In the fall, they turn attractive shades of yellow to red before dropping. The tree grows steadily to 35 feet tall and 15 to 20 feet wide.
At the southwest side of the bed, near some existing manzanitas, we added a specimen of our native mountain hemlock (Tsuga mertensiana). This remains one of my favorite small conifers for gardens of any size, with blue-green needles densely covering its short branches. Mountain hemlock is a slow grower and prefers sunny conditions. It can live for hundreds of years, but in cultivation it rarely reaches 20 feet tall by six feet wide, even after several decades.
Magnolia ‘Wada’s Memory’ in the flower.
Among the new trees, which were widely spaced to allow them to reach their full growth potential, we planted a mix of different shrubs. At the west side of the bed, adjacent to the manzanitas, we planted two cultivated varieties of chaste-tree from the Climate Ready Landscape Plants trial, recently completed at the CUH by UW researchers: Vitex Blue Diddley® (‘SMVACBD’) and Vitex Summertime Blues™ (‘Helen Froehlich’). Both are compact (growing up to five or six feet high) and drought tolerant, once established. They also offer handsome, compound foliage and spikes of lavender-blue, late-summer flowers.
I was also excited to plant a new species of osmanthus for the collections, Himalayan sweet olive (Osmanthus suavis). This was collected by Dan Hinkley in Nepal some years ago, at an elevation of nearly ten thousand feet. It forms a shrubby tree up to 12 feet high in the wild and bears clusters of fragrant, trumpet-shaped white flowers in April.
We also planted an example of Metapanax davidii, this one collected for Heronswood in the late 1990s in Sichuan Province, China, by Eric Hammond. A broadleaf evergreen, it is a tremendous foliage plant, featuring glossy-green, variably-shaped leaves—usually either simple (unlobed) or tri-lobed, but sometimes bilobed. In the wild, the species can become a small tree up to 20 feet tall, but in cultivation, it’s usually smaller and shrubbier. ❦
Ray Larson is curator and associate director of the University of Washington Botanic Gardens and a contributing editor for the “Bulletin.”
PHOTOS: Niall Dunne
The new mountain hemlock specimen by the Miller Library.
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This article is reprinted from the winter 2026 issue of the Arboretum Bulletin, our quarterly botanical and horticultural magazine. Published since 1937, the Bulletin is a benefit of Arboretum Foundation membership and features in-depth articles on the Arboretum collections and history, as well as general information of interest to plant lovers in the Pacific Northwest and beyond. Join/subscribe today.
