Stroll along wooded hillside trails amid a brilliant spring display of thousands of blooming azaleas while learning about the origins and culture of these popular shrubs. Thousands of the arboretum’s azaleas increased their vigor and blooms thanks to the Glenn Dale Hillside Renewal Project, a major renovation completed in 2014. More information is available below.
Admirers come to the U.S. National Arboretum’s Azalea Collections every spring to witness one of Washington’s premier spring attractions: thousands of azaleas covering the flanks of Mount Hamilton in a blaze of color. The first warm days bring out the flowers, and the slopes take on a surreal, almost luminescent glow. Few shrubs have more impact on the spring landscape–azaleas are an enduring favorite in gardens throughout the country.
Many of the shrubs in the collection sprang from the azalea breeding work of former Arboretum Director Benjamin Y. Morrison. The plants on the south slopes of Mount Hamilton in the area known as the Glenn Dale Hillside are the products of this work. Morrison envisioned the modern hybrid azalea as we know it today and successfully married the large flowers and exciting colors of tender azaleas in the Indica group with the hardiness of more northerly species. Morrison did the hybridization work in the years between 1929 and 1954. During this time, he first served as Chief of Plant Exploration and Introduction at the Glenn Dale Plant Introduction Station and later became the first Acting Director of the U.S. National Arboretum. The Glenn Dale Hillside was planted with 10,000 unnamed Glenn Dale hybrids from 1946 to 1948. Morrison went on to eventually introduce 454 cultivars of Glenn Dale azaleas.
In 1952, the walled Morrison Garden was built. It still serves as the hub that unifies the Azalea Collection today. Bricks from a schoolhouse located in what is now the Boxwood Collection were used to construct the walls of this garden and impart a sense of timelessness. As the shrubs matured in the 1950s, locals could not resist the colorful spring beacon of the blooms. Their desire to see the plants led to the opening of the U.S. National Arboretum to the public on a seasonal basis in 1949.
The Glenn Dale Hillside is perhaps the most spectacular in terms of number and variety of azaleas blooming within a short time period. Masses of some of the hundreds of hybrids developed by Morrison grow in contours on the steep slopes of Mount Hamilton. In the walled Morrison Garden, low hedges of boxwood complement the formal design that showcases individual azalea specimens. To the west of the garden, a large plaza shaded by the venerable branches of a mature lacebark pine, Pinus bungeana, serves as an ideal spot to contemplate the peace and beauty of wakening spring. To the north of the Morrison Garden, the Frederic P. Lee Garden spreads along the east slopes of Mount Hamilton to the Lee Garden Pond at the north end of the Azalea Collection. Late blooming azaleas planted near the pond extend the azalea season into May and early June.
The Lee Garden is arranged with different areas devoted to major varietal groups of azaleas that can be grown in the Washington area. The Henry Mitchell Walk, named in honor of the revered Washington Post garden writer, traverses the Lee Garden and tells the story of the development of these groups of hybrid azaleas. The diversity of colors and forms in the Lee Garden includes everything from low ground-hugging Satsuki azaleas with diminutive leaves and large blooms to bold upright deciduous native azaleas with smaller, more delicate flowers.
The best way to see this collection is on foot. A network of rustic woodland trails follows the contours of Mount Hamilton and allows you to view the blossoms at close range. If you want a bit of exercise, you can follow the trail to the top of Mount Hamilton, one of the highest points in the District of Columbia. At this elevation of 240 feet above sea image of ‘Golden Comet’ deciduous azalea level, you’ll be treated to a view of the Capitol framed by trees. If you’re planning a visit, wear shoes suitable for walking on uneven rustic trails. Park in the Administration Building parking lot and access the collection by walking a short distance south to the entrance to the Henry Mitchell walk. Most visitors want to take at least an hour to enjoy the blossoms, and many spend several hours admiring the azaleas. If you are not able to traverse the trails, a leisurely drive along azalea road is a good alternative. At the R Street Gate, take a right and bear to the right on Azalea Road. Follow this route past the Boxwood Collection to see the Azaleas. A sampling of Glenn Dale hybrids can also be seen from accessible areas around the Administration Building.
Peak bloom can vary by two weeks or more, depending on the weather, but usually takes place around the end of April. The earliest peak bloom date reported in the last decade was April 15; the latest was May 4. Keep in mind that many azaleas are in bloom long after the peak and others might bloom early–there are usually some azaleas in bloom from early in April until well into June.