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US National Arboretum


Azalea Blossom Watch 2011
Current Conditions

April 1 | April 8 | April 15 | April 22 | April 29 | May 6 | May 13 | May 20 | May 27

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. In 2011, the peak azalea bloom should be between April 22 and May 1. 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 1

Weston's Starburst Spring has returned to the Washington, D.C., area.  The National Arboretum staff is busily putting finishing touches on all the gardens.  Cherries and magnolias are in full bloom with the redbuds budding up in profusion. Some of the earliest of the Glenn Dale azaleas started to bloom on March 31st. With warm temperatures and sunny skies ahead, more buds should be open by next week.  Our projection for peak bloom is between April 22 and May 1, with many shrubs blooming before and after those dates.

Many people have asked if the freezes we had last weekend will affect the azalea bloom, and the answer is no.  Our temperatures have remained cool, and very few of the azaleas have started to open. Tightly closed buds can withstand our seasonal lows, but once the flowers start to show their color, they are vulnerable to spring frosts, which then will cause even slightly opened buds to freeze. Worry not, there are many more that will be fine.

This week in the collection you will find our usual early spring arrivals that bloom every year with the forsythia. Take a walk on the Henry Mitchell Cultivar Walk where you will see some early blooming rhododendrons, such as the double flowered ‘Weston's Starburst’, the deep majenta pink 'Landmark', and the pale pink ‘Llenroc’ (spells Cornell backwards), which was bred in Massachusetts by Ed Mezitt in 1939 using crosses with native Rhododendron carolinianum album and Korean Rhododendron mucronulatum.White and Pink selections of the normally lavender Rhododendron mucronulatum are also in bloom this week. These "small-leaved rhododendrons" are classified as lepidote rhododendrons, having small waxy leaves that persist through the winter.

See you in the garden!


April 8

R  Weston 'Landmark' Spring is slowly unfolding at the National Arboretum.  There are several azaleas in bloom that always bloom with the daffodils, cherries, and magnolias. They were bred to bloom early in order to extend the season of azalea bloom into early spring.

The Weston hybrids, which started to bloom last week, are still in bloom.  Weston's 'Landmark' is one to see with its striking deep magenta flowers and dark burgundy evergreen foliage. The Nearing hybrid 'Montchanin' is lovely with clusters of tiny pale pink flowers and dark evergreen leaves. Both plants are located along the trail across the road from the Capitol Columns Overlook. 

The Kurume hybrids are about to open any day, as are the Glenn Dale hybrids located on the south side of Mt. Hamilton.  One only need look closely to see colorful buds and a few opened flowers.  Several warm, sunny days will encourage more and more flowering. We hope to see you in the garden.



April 15

R  Weston Grp  'PJM Elite' April showers—you either love them or you hate them; however, it's definitely getting nicer outside. There have been ample rains and cool days this spring, so the peak bloom for azaleas will be towards the end of April. Right now, dogwoods are opening slowly, while the daffodils are still blooming gloriously. 

In the Azalea Collections, the Weston hybrids continue to blossom. Some later cultivars such as 'Olga', 'PJM Elite', and 'April Snow' have just opened. A wonderful purple rhododendron is now blooming. It is one we propagated from the late Bill Steele, a Pennsylvania nurseryman, and is a Phetteplace hybrid called 'Crater Lake'. We have several plants located in the beds of the loop area in the cultivar collection (up the hill from the Lee Azalea Garden). Since this cultivar is not typically tolerant of our Washington, D.C., summers, we're not sure how long it will survive , but for this spring, it is lovely. 

Another early azalea in bloom now is the staminate form of Rhododendron kaempferi 'Kinshibe'. This is located along our Henry Mitchell Cultivar Walk in the bed with the coral-salmon azaleas.

The Glenn Dale hillside is budding up all over and many flowers have begun to open. This will be a good week to visit and learn all about the early blooming Glenn Dale, Kurume and other azalea hybrids, too.


April 22

R stenopetallum 'Koromo Shikibu' NA24286 The cool, rainy weather we've been having this April has had the effect of slowing down the opening of the azaleas in the D.C. area. But this week the Glenn Dale Azalea Hillside is opening at a rapid pace thanks to Wednesday's 80 degrees. The National Arboretum azaleas are nearing peak bloom and will be in spectacular form by the weekend. In bloom today are the early Kurume and early Glenn Dale azaleas, as well as lilacs, dogwoods, and redbud trees.

One of the special features of the National Arboretum's Azalea Collections is the grouping of azalea cultivars by their hybridizers. Featured in and around the Morrison Azalea Garden are the Glenn Dales, developed by the arboretum's first director, Benjamin Y. Morrison. Just beyond the Morrison Garden is the Henry Mitchell Cultivar Walk. Follow the interpretive signs along this trail to discover groups of Robin Hill azaleas bred in New Jersey by Robert Gartrell; Kurume azaleas, which came into the United States early in the last century during plant exploration trips to Japan and the Far East; and more.

Planted in beds between the hybrid groupings are azaleas arranged by color. For example, we have a hillside of cultivars that bloom in shades of purple, lavender, or pale violet. On this bank, you will find specimens of Rhododendron macrosepalum var. linearfolium, a unique spider azalea, and 'Koromo Shikibu', another unusual form of the Japanese species Rhododendron stenopetallum. We have shades of red azaleas planted along both sides of the steps at the north end of the collection. Here you will find Gable's 'Flame', Harris's 'Midnight Flare', and the Beltsville Dwarf 'Flash', among others.


April 29

Azalea CollectionThe azaleas are now at peak. This means that the first ones to bloom are still looking great while the mid-season bloomers are bursting into full bloom.  The weather has been a little hotter than we would like (mid 80’s) and is causing some of the blossoms of the earlier varieties to drop early; however, with ample moisture from all of our spring rains, we are enjoying a banner spring season this year.

The coming week promises to be as beautiful as the previous two. The Kurume azaleas are finished blooming for the year, but now is the prime time to see what the Glenn Dale azaleas are all about. These hybrids were bred to have larger flowers and to extend the season of bloom for spring-flowering azaleas.  Some Glenn Dale azaleas such as ‘Nubian’, ‘Roundelay’, and ‘Quakeress’ will reach heights of over six feet and have flowers that are three inches in diameter. You can see over 200 specimens of Glenn Dale azaleas in and around the Morrison Garden, named in honor of the breeder of the Glenn Dales, and the arboretum’s first director, B.Y. Morrison.

The Robin Hill azaleas are starting to come out as well. Bred for shorter stature and beautiful blossoms, the Robin Hills are located in the Loop Area Collections along the Henry Mitchell Cultivar Walk.  Over 1,975 accessions of labeled plants are located along this walk, designed to teach people about the richness and variety of hybrid azaleas.

Located to the south of the Morrison Garden are eight acres of over ten thousand Glenn Dales planted between 1946 and 1947.  Seeing this colorful array of mature shrubs in person is a breathtaking experience. 


May 6

Morrison GardenThe Azalea Collections are still looking fantastic this week.  By the middle of the week, the temperatures cooled (mid 60s), and the rains stopped. The rain was good not only because the plants needed it, but also because the showers caused the spent blossoms to drop. The cool temperatures have slowed the opening of the mid- and later season cultivars.

Open now are some of our native azaleas. The coast azalea (Rhododendron atlanticum), native from Delaware south to Georgia, is one of the most fragrant of the North American species.  You will find it just outside the Frederic P. Lee Azalea Garden and along the Henry Mitchell Cultivar Walk just north of the Morrison Azalea Garden.  The coast azalea is extremely fragrant, so you can follow your nose to find it.  The yellow-orange native Florida flame azalea (Rhododendron austrinum) is in full bloom along the roadside in the Fern Valley Native Plant Collection—be sure to include a stop here when you visit.

Seen along the eastern entrance to the azaleas is 'Koromo Shikibu', which has a unique strap-like flower form and can grow to be a very large-sized plant.  A specimen of this cultivar can be seen in the Gotelli Dwarf and Slow-Growing Conifer Collection near the teahouse that is over 10' tall and 15' wide.  Another beautiful azalea at the eastern entrance to the Azalea Collections  is a yellow deciduous azalea called 'Sunny Side Up'. It was hybridized in Alabama by Gene Aromi, but grows perfectly well here in the mid-Atlantic region.


May 13

R. 'Martha Hitchcock' The weather this week has been superb for gardeners and plants alike. When the daytime temperatures are in the mid-70s and the nighttime temperatures are between the mid-40s and the mid-50s, flowers stay on longer and experience less stress. But be sure to water newly planted plants: While we have had ample rainfall this spring, the breezy, sunny days quickly dry out the soil.

The National Arboretum azaleas are definitely not over. The earliest bloomers have faded, but now is the time for the mid- and late-season azaleas. The Glenn Dales were bred to extend the season of bloom. The Morrison Azalea Garden—designed to showcase B.Y. Morrison’s Glenn Dale hybrids—is in its full glory. Come into the walled garden to see some of the best mid-season bloomers: ‘Buccaneer’ is covered with large red flowers, each with a distinctive blotch that makes the overall shrub sparkle. The mature shrub is only about 5' tall.  Red and white ‘Ben Morrison’ and purple and white ‘Martha Hitchcock’ both show off their beauty from a great distance. 

The blossoms of the Robin Hill and Satsuki hybrids are beginning to open. The Robin Hills are extremely hardy, have large single or double flowers, and tend to grow to five feet in height. They and other cultivar groups may be seen along the Henry Mitchell Cultivar Walk, located on the east side of the collections.

Large-flowered rhododendron hybrids are also in bloom this week. These are the ones with the larger evergreen leaves, such as Rhododendron fortunei (from China), R. yakushimanum (from Japan), and R. catawbiens (from North America).


May 20

R. 'Purpureum Elegans' Although most of the mid-season azaleas have dropped their flowers for the year, late-blooming azaleas continue to color our collection with brilliant hues, and many have flowers that are 2 to 4 inches in diameter. There are reds, pinks, lavenders, and whites of all shapes and growth habits in bloom this week.

The North Tisbury hybrids are selections of Rhododendron nakaharai, a late-blooming and predominately low-growing species from Japan. These azaleas will always bloom in mid- to late May and most are available at local nurseries. Look for ‘Joseph Hill’, ‘Pink Pancake’, and ‘Mt. Seven Star’ along the Henry Mitchell Cultivar Walk.

The Robin Hill azaleas are nearing their peak period of bloom, and the Satsuki hybrids are still surprising us with their unique and delightful blooms.  Large-leaf rhododendrons, such as the ever popular ‘Roseum Eleagans’, are in full bloom this week with it’s large purple flower trusses . 

Now is the time for the Flame Azalea (Rhododendron calendulaceum) to make its appearance with brilliant orange flowers.  Originally found in the Southern Appalachian Mountains, seed was collected from this deciduous native azalea and found to be perfectly hardy in our gardens.   We have planted them in various locations throughout the cultivated section of the collection.  We also have added a collection  of cultivated mountain laurel (Kalmia latifolia). These have interesting flower variations from plant to plant; some have spectacular dark pink or red buds before opening up to a lighter hued flower and can be found near the north entrance to the Azalea Collection near the Visitor’s Center Trailer.

The ample rains of this spring have been great for our azaleas, but a little rough on our trails. Be sure to wear sturdy shoes when you visit.


May 27

R. Satsuki 'Shinyomo no Haru' The fragrance of honeysuckle is drifting through the air. This week the Azalea Collections still offer a lot of color, but for the most part, one is struck by the lush greenness of it all, and other plants begin to draw our attention. In the stately Morrison Garden, the blooming climbing hydrangea softens the edges of the garden, and the yellow variegated dogwood 'First Lady' stands out against the dark red 100-year-old brick.

For the azaleas, now is the time for the larger-flowered and double-flowered varieties to begin their blooming. One needs only to climb the steps at the north entrance to the Azalea Collections to the Frederic P. Lee Garden and surrounding beds to discover the full color spectrum of the late-blooming azaleas. This garden was designed to showcase these season-extending shrubs.

The North Tisbury 'Eiko San', with its salmon-red double flowers, is the first of the North Tisbury hybrids to bloom. The doubled-flowered form of the Japanese Riverbank azalea, Rhododendron indicum 'Balsaminiflorum' and the Satsuki hybrid 'Beni Kirishima' are two doubles one may see today. The Robin Hill hybrids 'Whitehead', 'Corry', 'Mrs. Villars', 'Mrs. Emil Hager', and 'Sara Holden', as well as many others, are in full bloom. Their flower diameters reach 3½ inches or more across. Several of the Robin Hill azaleas feature sporting branches, or branches that carry blossoms of a different color from the dominant one. This is due in part to the Satsuki azaleas used in their breeding—Satsuki azaleas are prized for the appearance of multiple colors on a single plant. Many of the Satsuki hybrid azaleas in our collection are also blooming.  The North Tisbury, Robin Hill and Satsuki hybrid groups are planted in and around the Frederic P. Lee Azalea Garden.  With the hundreds of cultivars in flower around the Lee Garden, one could think it’s early spring all over again.

This will be our final installment of the 2011 Blossom Watch.  But this doesn’t mean the azalea collection stops blooming.  We have perennials such as daylilies, phlox and others to enhance your woodland walk through our trails.  We hope to see you in the garden.

Click here for other images of the collection.

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Last Updated   May 27, 2011 2:17 PM

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