NATIONAL ARBORETUM’S SCIENCE, BEAUTY, AND IMPACT
Photo courtesy of the U.S. National Arboretum
OVERVIEW
The U.S. National Arboretum is a world-class center for horticultural research, education, and innovation. It spans 451 acres in Northeast Washington, D.C., and is administered by the U.S. Department of Agriculture Agricultural Research Service. The National Arboretum serves as both a horticultural research facility and a public garden.
For almost 100 years, the National Arboretum has played an important role in preserving germplasm, developing and introducing improved plants for the American nursery industry, bridging cultural connections through plant collections, restoring habitat, and more. Continue reading to learn more about key accomplishments that highlight the Arboretum’s science, beauty, and impact.
ROOTED IN RESEARCH: FLOWERING CHERRY TREES
The iconic flowering cherry trees around the Tidal Basin in Washington, D.C., explode into bloom all at once each spring. Nearly all of the trees are the same white-blooming cultivar, Yoshino (Prunus ×yedoensis), so the stunning display fades just as simultaneously after a few days.
Fortunately, the blooming bonanza continues at the U.S. National Arboretum. Here, hundreds of flowering cherries — 70 different species and cultivars — bloom at different times with varying colors, shapes, and sizes. The diversity of the Arboretum’s collection makes it truly unique. In addition to offering nearly a month of cherry blossoms, these captivating bloomers also store important genetic material for plant breeding and research.
Prunus ‘Dream Catcher’, an Arboretum introduction, in full bloom. Photo courtesy of the U.S. National Arboretum.
Roland Jefferson (left) and Donald Egolf (right) transformed the National Arboretum’s flowering cherry program into a world-class center for breeding genetic preservation. Photo courtesy of the U.S. National Arboretum.
For decades, the Arboretum has maintained one of the largest and most significant cherry collections in the world — with more than 1,500 genetically diverse trees. Some are squat and wide. Others are tall and narrow. There are weeping varieties with branches that drape like curtains to the ground. Bloom time brings an eye-popping array of blossoms, ranging from delicate single petals to dense, ruffled, multi-petaled clusters in colors from pure cloud white to deep, vibrant pink. The Arboretum’s horticulturists and scientists preserve these unique genetic resources, keeping them safe and available for research and breeding.
The National Arboretum’s flowering cherry breeding and preservation program is just one example of the high-impact scientific research conducted here. Arboretum scientists work to develop improved varieties of shrubs, trees, and turfgrasses to support the nursery industry. The work helps ensure that future generations can continue to enjoy the beauty of flowering cherries and other beloved plants — not only in Washington, D.C., but in communities across the country.
Much of the Arboretum’s scientific stewardship of flowering cherries was shaped in the 1980s through the collaboration between research geneticist Dr. Donald Egolf, who led the Arboretum’s shrub-breeding research program, and botanist Roland Jefferson. Egolf’s breeding expertise, combined with Jefferson’s collecting expeditions abroad and propagation work, expanded the Arboretum’s flowering cherry collection and strengthened its genetic diversity. Their efforts also helped position the Arboretum as a global player in ornamental cherry research.
For decades, the Arboretum’s cherry breeding program prioritized trees that are as structurally sound as they are visually striking. Researchers evaluate and select for features such as earlier bloom times, larger petals, and distinctive blossom colors. Plant geneticist Dr. Margaret Pooler built on this foundation in recent years, using modern genetics to enhance aesthetic traits, disease resistance, and environmental stress tolerance in flowering cherry, crapemyrtle, and redbud trees. This work directly supports plant nurseries and provides communities nationwide with trees better suited to thrive in today’s landscapes.
Arboretum scientists have selected and released four flowering cherry tree cultivars into the American nursery industry. The rigorous selection, propagation, and trial process may take 15 years or more before a new tree is considered ready for the trade.
Prunus ‘Dream Catcher’
The first cultivar introduced from the Arboretum’s flowering cherry program in 1999, it features large, light-pink, single blossoms in early spring. Its initial upright, vase-shaped form gradually develops a broader, more rounded crown at maturity.
Prunus ×incam ‘First Lady’
An upright, deep-rose pink flowering hybrid. This early bloomer, officially released by the Arboretum in 2003, was selected for its cold-hardiness.
Prunus campanulata ‘Abigail Adams’
Features rare dark pink, semi-double flowers. It was released in 2013 primarily to make this genetic resource available to growers and breeders, particularly for developing cherry trees suitable for warmer climates.
Prunus ‘Helen Taft’
Named for First Lady Helen Taft, who championed the original 1912 cherry plantings at the Tidal Basin. A clone of a tree she planted at the historic event was crossed with a Taiwan cherry to create this hybrid. This early bloomer features large, pale-pink flowers and tolerates warmer Southern climates. It was released in 2012.
SHAPING AMERICAN LANDSCAPES: AZALEAS
Each spring, Mount Hamilton at the U.S. National Arboretum erupts into a sweeping tapestry of color. Azalea shrubs stud the hillside with flowers bursting in pinks and purples among shocks of light yellow and snow white. The National Arboretum’s Azalea Collections provide a breathtaking display — but behind the blooms are decades of research that shaped American horticulture.
In the 1930s, the National Arboretum’s first director, Benjamin Y. Morrison, set out to solve a practical problem: how to expand the range of large-flowered azaleas available to American gardeners in colder climates like Washington, D.C.
Azaleas belong to the genus Rhododendron in the broader heath family (Ericaceae). Many of the popular varieties with large flowers that thrived in the southern United States struggled to survive winters north of Virginia. Morrison believed beauty and hardiness could coexist. He launched an ambitious breeding program that ultimately transformed the nursery industry — and America’s landscapes.
Azalea Collections hillside in full bloom. Photo courtesy of the U.S. National Arboretum.
Benjamin Y. Morrison, the National Arboretum’s first director, began the azalea hybridizing program in the late 1920’s. Photo courtesy of the U.S. National Arboretum.
Over time, the program produced 454 named Glenn Dale hybrid azaleas — a remarkable achievement in ornamental plant breeding. Carefully bred from diverse hybrids and Asian species, they featured larger blooms and expanded colors beyond what had been previously available in cold-hardy azaleas. The Glenn Dale azaleas opened new possibilities for gardeners across the Mid-Atlantic and beyond. They now inspire gardeners and support nurseries throughout the region. These plants are proof that the research happening behind the scenes at the National Arboretum is about much more than flowers — it’s about offering a wide array of plants that can transform American gardens.
The Azalea Collections quickly became one of the Arboretum’s defining features. These striking blooms spurred the National Arboretum to open its gates to the public on select weekends every spring beginning in 1949. Over the next decade, the National Arboretum continued to develop its research collections with the added purpose of public education and enjoyment. Visitors could finally see firsthand how federal plant research is translated into living landscapes. Today, the azaleas are a highlight of the Arboretum’s blooming calendar, drawing families, photographers, gardeners, and plant lovers each spring. Peak bloom can vary due to weather and variety. Fortunately, the wide array of azaleas includes later-flowering varieties that stretch the impressive show into June.
Rhododendron ‘Pied Piper’
A compact shrub with white blooms that are flushed with pale amaranth pink and streaked with heavy magenta stripes and flakes.
Rhododendron ‘Fashion’
Vivid salmon-orange to red flowers feature one set of petals inside another, creating the appearance of double flowers. This popular Glen Dale hybrid blooms heavily in spring and often reblooms in fall.
Rhododendron ‘Ambrosia’
An early-spring bloomer with interesting salmon-pink to light orange-yellow flowers.
Rhododendron ‘Glacier’
A compact shrub with white blooms that are flushed with pale amaranth pink and streaked with heavy magenta stripes and flakes.
Azalea introduction photos courtesy of the U.S. National Arboretum.
BRIDGING CULTURES THROUGH BONSAI
Stay tuned — this section is coming soon!
SPRINGHOUSE RUN RESTORATION
Stay tuned — this section is coming soon!
