Your browser does not support script.
US National Arboretum


Azalea Blossom Watch 2010
Current Conditions

March 19 | April 2 | April 9 | April 16 | April 20 | April 29 | May 5 | May 21


Experience the National Arboretum's treasured Azalea Collections.

Spring is upon us once again. The National Arboretum is once again a place rich with bloom – from the spring ephemerals to the daffodils, magnolias and cherries planted through out the grounds. This column which begins today and will change each week for the next eight weeks will focus specifically on our Azalea Collection 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. In 2010, the peak azalea bloom should be between April 24 and May 2. 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 Blossum Watch will give you insight into the range and diversity of Rhododendron species and cultivars growing at the National Arboretum, as well as help you with arranging your plans for a visit.

Images of azalea blossoms

The best time to schedule your visit is on a week day, 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 and take a walk, it is worthwhile. Park in the nearby M Street parking area, and walk to the Morrison Garden. Pick up a brochure there, 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.


March 19th

image of 'Allure'

This winter’s heavy snow did not hinder the azalea bloom time whatsoever. Other than a few split branches, the azaleas are fine. We will probably be working on pruning out these splits for months to come, because they don’t always die, and will still produce blooms if the buds are there.

When is the peak?
Folks who wish to target their visit for the peak azalea bloom can choose between the weekends of April 24-25 or May 1-2. I think this year in particular, we are on the later side of normal, and so May 8-9 (Mother’s Day is the 9th) will also be a great bloom weekend.

When do the earliest azaleas start blooming?
As early as April 1, but the Kurume azaleas and those that have a southern exposure such as our Glenn Dale Hillside, will really start blooming en masse by April 15.

The earliest of our rhododendrons is in bloom today. Rhododendron mucronulatum, the Korean rhododendron, may be seen around the Morrison Garden (lavender flowers) and throughout the cultivar collections (toward the Lee Garden).


April 2nd

Cherry treesThis week, the Azalea Collection has many buds showing a hint of color forecasting the brilliant display to come in the next few weeks. Beautiful flowering cherries and magnolias are in bloom throughout the National Arboretum grounds. Daffodils and other spring flowering bulbs also adorn the gardens. Weston Group Azaleas

Early species such as Rhododendron mucronulatum and the Weston hybrids are in bloom today and can be counted on to bloom every year with the forsythia.

Breakage from this February’s snowstorms continues to be on the top of our to-do list. It is important to prune out below these breaks EVEN IF IT LOOKS LIKE THEY ARE GOING TO SURVIVE. The cracks may appear to heal but can become infected with fungal diseases such as Botryosphaeria (azalea dieback) which will eventually spread throughout the plant and are also vulnerable to breakage later on.

Azaleas can be planted at this time of the year, but will not tolerate wet or saturated soils. Rainy weather and water seeps have saturated our turf areas throughout the arboretum, so care must be taken to park only in designated areas. The weekend is predicted to be sunny and mild. We’ll see you in the garden!


April 9th

R. Kurume 'Aya no Kamuri'
Temperatures soared to the low 90’s Tuesday and Wednesday this week at the National Arboretum. This is quite warm for the first week of April. Many of the early daffodils, cherries, and magnolias have quit blooming for the year due to the heat and warm temperatures will speed up the opening of early azaleas too. But they won’t like it and may wilt if planted in full sun. This is one of the reasons we like to recommend planting azaleas under the shade of tall oaks or along the north side of your home or building. They need sunlight to set bud and bloom, but dappled light in our region is best. Azaleas that are showing color and opening up this week include many on the historic hillside of Glenn Dales (between 5-10%, early for our area), the Kurume azaleas, and the Weston hybrids which were flowering last week are still in bloom this week.



April 16thMitchell Walk

The azalea collection is looking spectacular this week with opened Kurume hybrid azaleas along with hundreds of early Glenn Dale hybrids. The Glenn Dales, hybridized by the first director of the National Arboretum, B. Y. Morrison, are featured in the Morrison Azalea Garden, a formal bricked garden, lined with boxwood hedges and ornamental trees. Surrounding this garden are acres and acres of azaleas. Morrison used many Kurume azaleas as parents of his Glenn Dale hybrids, which impart the early blooming characteristic. This is where the similarity ends. Most Glenn Dale azaleas have large flowers (greater than 2 inches) while the Kurumes typically have 1 to 1½ inch diameter flowers, produced in abundance.

Sprinkled among the evergreen azaleas are selections from our own North American native azaleas such as the Florida Flame Azalea (Rhododendron austrinum) and the Pinxter Azalea (Rhododendron periclymenoides) which can be found growing in woods in the Washington D. C. area.


April 20th
R  GD 'Advance'

The azaleas are in full swing at the Arboretum this week and should look great by the weekend. The cool weather predicted will really prolong the blooms. We have an important notice, however, before you get in your car to come visit.

The Azalea Collection will be closed either Wednesday April 21st or Thursday April 22nd (depending on weather conditions) in order to treat them with a fungicide for preventing petal blight. The application of this spray is something we do every year at this time. We strongly recommend that you call first to find out the status: (202) 245-4523. The roads will remain open for driving past the display, but the trails and paths will all be closed for the day. We apologize for this inconvenience.

Thousands of cultivars are planted in the 30+ acres of the azalea collection. We have them labeled for study and comparison. Most azaleas grow very well in the Washington D. C. area due to the abundance of oak leaves and acid soils in our region. They usually need to be given extra water during drought summers, but otherwise are relatively easy to grow. Large-flowered Glenn Dales and diminutive Kurume azalea hybrids comprise 90% of the display this week; and we have several deciduous azaleas in bloom as well. 'Aromi Sunrise' is a brilliant orange and can be seen from the road. Be safe, call first. And enjoy this nice weather!



April 29th
R. RH 'Nancy of Robinhill'

It is the end of April and the mid-season azaleas are in bloom early this year. This past week’s rainfall knocked off the flowers from the early azaleas which had been blooming for two weeks, and now the mid-season bloom is upon us. We are about ten days ahead of normal this year because of the two extremely warm days we had in early April. Thanks to above-freezing cool nights, the bloom has been spectacular with more to come.

Coming into bloom now are the Glenn Dale hybrids selected for their later season of bloom. Cultivars like ‘Oriflamme’, ‘Refrain’, ‘Elizabeth’, and ‘Mary Margaret’ will always bloom just after the Kurume azaleas. The Robin Hill azalea cultivars are also coming into bloom with their large Satsuki-like flowers. Selected for smaller landscapes, these cultivars will ultimately grow lower than the Glenn Dales, but will have large glowing blossoms during the mid and late seasons of spring. Choose cultivars such as ‘Nancy of Robinhill’, ‘Jeanne Weeks’, ‘Corry’, or ‘Sara Holden’ to brighten up your gardens. Come to the National Arboretum to see the whole spectrum of Glenn Dale and Robin Hill cultivars.


May 5th

R. atlanticumIf you drive around Azalea Road this week, you may think, “the azaleas are over!!” but this is not the case! The mid-season azaleas are still in bloom but you will need to take a short walk in order to find them. There are thousands of flowers still showing beautiful color throughout the cultivated section of the Azalea Collection which is the section that faces the Capitol Columns or the east. This includes the Morrison Garden, The Lee Garden, The Henry Mitchell Cultivar Walk, and the surrounding areas. We have azaleas grouped by color or by hybrid group. The Glenn Dales, Back Acres, Robin Hills, and the large color groups (red, purples, whites, pinks, and salmons) are in full bloom this week.>

Dotted through these displays (which are for the most part selected from Japanese species azaleas), are several native azalea species raised from seed collected from our own eastern United States. The Flame Azalea (Rhododendron calendulaceum) is orange and is coming into bloom this week. The Coast Azalea (Rhododendron atlanticum) is white, extremely fragrant, and native to the eastern parts of Deleware, Maryland, Virginia, and the south.


May 21st

Lee GardenThis will be the last entry for this year's azalea blossom watch because most of them have finished blooming. There is a reason for an entry at this time, however, and that is because there are still hundreds of azaleas in bloom now. These are the late-blooming North Tisbury hybrids, the Robin Hills, and most importantly, the Satsuki hybrid azaleas.

Most of them can be seen in full bloom in the vicinity of the Frederic P. Lee Azalea Garden, located up the hill from the Friendship Garden on the north side of the collection. I have spread them around and fanned them out from the Lee Garden to entice you into the garden.

You will find the low-growing, ground-hugging North Tisbury azaleas to be perfect for the front of a perennial or mixed border bed. Right now, the flowers of ‘Trill’, ‘Gabrielle Hill’, ‘Alexander’, and many others decorate key turns and entrances in the collection.

The Robin Hill azaleas combine the lovely floral features of the Satsuki and Glenn Dale azaleas on a more reasonably sized plant. Growing to less than 5 feet in 20 years, the Robin Hills are a perfect plant for the smaller garden. Cultivars such as ‘Sara Holden’, ‘Mrs. Villars’, and ‘Lady Robin’ even have multi-colored sports of white/pink flowers in various combinations.

And talk about combinations of colors, shapes, and sizes, the Satsuki hybrid group which comprises 100 - 300 cultivars, and were brought to the United States from Japan, contain many unusual forms, sizes, and colors. Now is their time for show in May, “the fifth month”. The Azalea Collection has about 100 cultivars in bloom now in and around the Lee Garden. I’ll see you in the garden!


Click here for other images of the collection.

 Back to the Arboretum Home Page
Arboretum Information || Events & Education || Gardens & Horticulture || Research Activities
Support the Arboretum || New Plant Introductions || USDA Plant Hardiness Zone Map || Comments
Search Our Site

Last Updated   May 21, 2010 2:12 PM

Please address any comments or questions regarding any portion of this web page by e-mail to the FNPRU site administrator