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US National Arboretum


Azalea Blossom Watch 2015
Current Conditions

April 3 | April 20 | April 27 | May 14

Experience the National Arboretum's treasured Azalea Collections

Spring is upon us once again, and the National Arboretum is rich with bloom from the spring ephemerals to the daffodils, magnolias and cherries planted throughout the grounds. This column which begins today and will change each week for the next eight weeks will focus specifically on our Azalea Collections and the status of bloom.

Experience the explosion of color when thousands of azaleas at the National Arboretum light up the forest with their subtle shades and colors.However, the first azaleas begin to bloom in early April with the daffodils and the forsythia, and still others are blooming as late as July with the daylilies. We hope that this Azalea Blossom Watch will give you insight into the range and diversity of the Rhododendron species and cultivars growing at the National Arboretum, as well as help you with planning your visit.

Images of azalea blossoms

The best time to schedule your visit is on a weekday, but if weekends are your only option, a stroll through the garden before noon or during a light rain offers an enviable second choice. A drive around Azalea Road can be exhilarating because of the views of the collection, but if you can afford the time to take a walk, it is worthwhile. Pick up a brochure at one of the three major entrances to the collections or at the Visitor Information center and begin your journey into the world of azaleas.

Learn more about the Azalea Collection here. For more in-depth information on growing and caring for rhododendrons or azaleas, check out the FAQ pages here. Visit our Azalea Photo Gallery where you will find over 200 images of the flowers of more than 100 of the Glenn Dale azalea varieties.

In the meantime, check back here each week as we update you on the current conditions in this year's Azalea Blossom Watch.

April 3

Greetings to our friends and guests!
Today we begin our weekly azalea blossom watch updates. For the next eight weeks, Azalea Collections Curator Barbara Bullock will describe the azaleas as the season unfolds.

Peak Bloom Prediction
Spring is taking the slow approach this year. With temperatures hovering on the cool side, (daytime averages in the mid-fifties throughout the month of March), the azaleas are not quite ready to show their colors. As long as temperatures remain cool, we predict peak bloom to be around the end of April or early May. 

Current Conditions
Very few early Rhododendron species are beginning to show color in the Azalea Collection.,  This week R. mucronulatum (lavender), swollen buds of R. keiskei (pale yellow) and R. reticulatum (pinkish-lavender) are ready to open any day.  This spring, cherries, magnolias, and daffodils are blooming later than usual due to the cool temperatures. 

Bald Eagle Nest On Glenn Dale Hillside
We are excited to report that a family of bald eagles have built a nest in a tall poplar tree situated among the Glenn Dale azaleas.  To learn more about the eagles,  you can visit our website: We have temporarily closed a portion of the Azalea Collection (about 30%) to preserve and protect them while they raise their young.  When visiting the collection, you will not be able to drive around Azalea Road until early summer, but you can easily view most of the garden if you walk from one of the Arboretum parking lots.

April 20

azaleaThis week, the Azalea Collection has many buds showing a hint of color forecasting the brilliant display to come in the next few weeks. Last week, temperatures soared to the low 80’s. This is quite warm for the early flowering plants like daffodils and many of the cherries and magnolias, speeding up their blooming period. The warm temperatures will also speed up the opening of early azaleas.  

Early species such as Rhododendron mucronulatum, and the Weston hybrids are in bloom today. They consistently flower at the same time that forsythia in is full bloom.  The evergreen azaleas that are showing color this week include many of the Glenn Dales which are planted in and around the Morrison Azalea Garden, and the reliable but beautiful Kurume azaleas found along the Henry Mitchell Cultivar Walk.  A few of our native deciduous species such as Rhododendron austrinum (the Florida Flame Azalea) will be in bloom by the end of the week. 

For information on when and how to prune azaleas, when the best time to plant and transplant azaleas and much more, check out our FAQ link at:

See you in the garden.


April 27

Peak bloom for the Azalea Collection will be the weekend of May 2nd and 3rd, producing a spectacular show of color. Cool temperatures in early April delayed many of the earlier blooming plants such as the dogwoods, the Weston hybrid azaleas, and lilacs.  Additionally , the cooler temperatures we’ve experienced this week has extended  their  blooming period along with the earlier evergreen azaleas known as the  Kurume hybrids. 

The Kurume azaleas were brought to North America from Japan. The  Kurumes are hybrids of numerous species from Japan, and according to E. H. Wilson [Plant Hunting, Vol. II, and A Monograph of Azaleas,] they were developed by Mr. Motozo Sakamoto, a Japanese samurai, in the 19th Century.  In the early 20th Century, they were widely cultivated and given new cultivar names like ‘Snow’, ‘Hino-Crimson’, and ‘Coral Bells’. They became a mainstay of American gardens where azaleas thrive.  They were also used extensively in the breeding of the National Arboretum’s Glenn Dale azaleas.  Earliest to bloom, and having a nice form, they are in bloom today in the Azalea Collection.  Pictured here, ‘Osaraku’ is lavender with a white center, tinged with greenish yellow for a lovely garden effect. 

The Glenn Dale Azalea Hillside is filling in after the azaleas were rejuvenated several years ago.   This year, about 60% of the hillside is closed off to the public due to a family of bald eagles nesting there for the first time in over 60 years.   With Azalea Road closed and a large section of the hillside closed, we recommend that you consider parking in the main lot, and walk into the collection of hybrids we have been assembling as a reference collection since the late 1950’s. 

See you in the garden!

R. Kurume 'Oogocho'R. Kurume 'Azuma shibori' syn. 'Snow'R. Kurume 'Osaraku'

May 14

The time to visit the Azalea Collection is now!  The collection is in spectacular form.  Our later spring, combined with the mild temperatures we are experiencing, has made this one of the better years to view the later blooming azaleas. 

The mid-season azaleas are currently in bloom.  In addition to breeding for larger flowers, a primary goal of the Glenn Dale azalea hybridization project was to extend the blooming season. The Glenn Dale group tolerates the warmer temperatures occurring in May.  They and the Robin Hill hybrids represent the majority of the mid-season bloomers, which are located thoughout the collections  A few of the azaleas in bloom this week include ‘Ben Morrison’, ‘Glacier’, ‘Boldface’, ‘Mayflower’, ‘Galathea’, ‘Kobold’, and ‘Fawn’. There are many others as well. Larger leafed rhododendrons and deciduous cultivars and species are also in bloom, including R. austrinum, R. calendulaceum, R. atlanticum, R. oblongifolium, and R. molle. ‘Zoe Graves’ and ‘Caroline Gable’ are representative of the large-leaf rhododendrons.

In the next few weeks, the late-season blooming azaleas will be coming into their prime. Many of these are planted in and around the Lee Garden.  Other later blooming evergreen and deciduous azaleas, rhododendrons, and mountain laurels will also be in bloom during the next few weeks.

Enjoy the display and take time to appreciate the wide variety of color, form, and size of these wonderful shrubs.  See you in the garden! 

See you in the garden!

Click here for images of the collection.

You can also read the Azalea Blossom Watch from
2014, 2013, 2012, 2011, 2010, 2009, 2008, 2007, 2006, 2005, and 2004.

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Last Updated   May 14, 2015 3:23 PM

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