Experience the National Arboretum's treasured Azalea Collections.
Experience the explosion of color when thousands of azaleas at the National Arboretum light up the forest with their subtle shades and colors. In 2008, the peak azalea bloom should be between April 20-30. 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.

April 2nd

Spring has returned to the Washington D. C. area. The National Arboretum staff is busily putting finishing touches in all the gardens. Cherries and magnolias are in full bloom with the redbuds budding up in profusion. Several of our first Glenn Dale azalea cultivars have already started blooming – specifically 'Allure' (see image at left) and 'Dayspring'. One has to search the massed Glenn Dale Azalea Hillside, but there are plants nearing full bloom scattered among the thousands of azaleas facing Azalea Road.

Daffodils and other spring flowering bulbs adorn just about every corner of the National Arboretum. Check out the brand new perennial planting located on the south entrance to the Morrison Garden. Once a monochromatic mat of juniper and vinca, this new planting features hundreds of new perennials and a few thousand bulbs, mainly in the blue and orange color scheme which will continue to interest and delight the visitor as they pass.

The number one question we have been asked this year is whether the stresses of last year’s terrible drought will affect this year’s spring bloom. The answer is two fold. We have had to prune out a lot of branch die back resulting from the drought stress, (see pruning FAQ) but we are happy to report that the remaining healthy branches are budding up and slated to bloom as usual. In our area, it is always possible that a late freeze could damage buds that have already begun to show color. For the time being, plan on the peak bloom of the azaleas at the National Arboretum to be between April 20 and April 30.

April 9th

The warm weather we’ve had this week is bringing out more and more azaleas. The Glenn Dale Azalea Hillside, planted in 1946 with thousands of Glenn Dale azaleas, is showing all sorts of color at this time. Some of the early Kurume azalea cultivars have also started to open.

Take a walk on the Henry Mitchell cultivar walk where you will see some early blooming Rhododendrons such as 'PJM' (see image at right) and 'Llenroc' (spells Cornell backwards) which were bred in Massachusetts by Ed Mezitt in 1939 using crosses with native Rhododendron carolinianum album and Rhododendron mucronulatum or Rhododendron dauricum – these species are represented and blooming in the collection today. These are classified as lepidote rhododendrons, having small waxy leaves which persist through the winter.

There was a freeze warning predicted in our area for the night of April 15, and so the azalea blossoms that are showing any color could be damaged. If we could, we’d put a blanket over the whole lot for the night. Let’s hope for the best. The Glenn Dale Azalea Hillside is showing a lot of color. The very early Glenn Dales in the Morrison Garden such as 'Dream', 'Allure', and 'Dayspring' are still in full bloom. The daffodils are nearing the end of their blooming season, but the dogwoods are ready to open very soon – they just need a couple of warm days.

The Kurume azaleas with their small hose in hose flowers of all colors are coming into bloom now. Visit the Wilson Kurumes (first brought into this country in 1917 from the Oishi Gardens at Hatageya, north of Tokyo), located along the Henry Mitchell cultivar walk. The Weston Rhododendron selections such as 'PJM', 'Landmark', 'Vallya', 'Pink Discovery', 'Olga' are in spectacular bloom and should still look great for the weekend.

Many cultivars of the Japanese Andromeda (Pieris japonica) are in bloom through out the collection. There is even a white flowering form of our native redbud, Cercis canadensis in bloom this week.

This week, the National Arboretum azaleas are nearing peak bloom and will be in spectacular form by the weekend. The Friends of the National Arboretum (FONA) plant sale is being held on Saturday, so parking will be at a premium. Our tip to all of you is to come early and to park at our M Street parking and picnic area where there is usually plenty of parking. It is a short walk to the Azalea Collection; and when you return, there is a restroom close by and plenty of picnic tables for you to use. There is also going to be a shuttle service to the plant sale from this parking lot.

One of the features of the National Arboretum’s Azalea Collection is how we have arranged groups of azaleas by their hybridizer with the Glenn Dales featured in and around the Morrison Azalea Garden. The Henry Mitchell Cultivar Walk is marked on the trail brochure, and will guide you through collections of Robin Hill azaleas bred in New Jersey by Robert Gartrell; the Kurume azaleas which came into the United States early in the last century during plant exploration trips to Japan and the Far East. There are other later blooming hybrid groups which I will feature in later Blossom Watches.

Planted in beds between the hybrid groupings are azaleas planted by color groups such as a hillside of cultivars that bloom in shades of purple, lavender, or pale violet. In this bank, we have planted Rhododendron macrosepalum var. linearfolium, a very unique spider azalea, and 'Koromo Shikibu' another unusual form of the Japanese species, Rhododendron stenopetalum. 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.

The azaleas are still at their peak this week. There is something new in the azalea collection this year and that is the presence of fragrance. During the past 5-6 years, we have been adding native azalea species and cultivars to the collection and with that has brought the fragrance of the coast azalea, Rhododendron atlanticum, and the Florida flame azalea, Rhododendron austrinum as well as their hybrids and cultivars. Some of the cultivars to see are the Bovee hybrid 'Balls of Fire', a hybrid of Gene Aromi, 'Aromi Sunrise', and the old Knap Hill hybrid 'Blizzard', among others.

The Glenn Dale azaleas, which were introduced by the National Arboretum in the mid-1950’s are in full display on the hillside that you would drive by if you take Azalea Road. If you have the time to take a look, they are labeled and displayed in the Morrison Garden, a formal garden situated in the center of the Azalea Collection and a short walk from the M Street parking and picnic area.

The Kurume and Robin Hill hybrid azaleas are also in bloom. This week will be the last week for the Kurume blooms but the first week for the Robin Hills. Other hybrid groups of azaleas represented are Gable, Hirado, Beltsville, Pericat, and Shammarello. Come for a stroll or take a look at the labels and compare to what you have in your garden.

Azaleas are still opening this week at the National Arboretum's azalea collection. The Morrison Garden (see image at right) is in peak form featuring the Glenn Dale azaleas which were bred particularly to extend the spring azalea blooming season. B.Y. Morrison concentrated on the selection of later blooming azaleas using crosses he made with Satsuki hybrids brought back form Japan in 1939. The larger flowered Glenn Dales are a result of his work. Over half of the 454 introduced Glenn Dales are later blooming and planted in and around the Morrison Garden.

Rhododendrons and Kalmia selections are also coming into bloom at this time. While all azaleas are botanically classified as Rhododendrons, the larger leaf varieties are later blooming than many azaleas, with huge ball trusses of bell-shaped flowers and larger waxy leaves. Planted among the thousands of cultivated azaleas are native azalea species grown from seed collected from the Southern Appalachians, such as Rhododendron austinum, Rhododendron atlanticum and R. calendulaceum.

The main peak of azalea bloom has passed for yet another spring. Today, however, many late bloom Glenn Dales are opening up after waiting for all that rain to pass. We also have many other late blooming azaleas such as our Satsuki, North Tisbury, and Robin Hill hybrids coming into their season of bloom, which is typically after the peak season.

The azalea collection did not escape the heavy winds of this past Sunday unscathed. We had three huge trees come down in the storm, causing us to have to close certain sections of collection trails. While work is being conducted to remove these trees, we have placed barricades to notify our visitors to steer clear of the areas. The Henry Mitchell Cultivar walk is still open, and is accessed easily from the north trail opposite the Friendship Garden and Gift Shop.

Late blooming azaleas continue to color our collection with brilliant hues. There are reds, pinks, lavenders, whites of all shapes and growth habits blooming in the azalea collection this week. The Robin Hill hybrid azaleas are nearing their peak period of bloom while the North Tisbury and Satsuki hybrids will be opening over the next few weeks. Large leaf rhododendrons such as the ever popular 'Roseum Eleagans' are in full bloom this week with their 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 also have added a collection of cultivated mountain laurel (Kalmia latifolia). These have interesting flower variations from plant to plant; some have dark pink or red buds before opening up to a lighter hued flower.

The ample rains of this spring have been great for our azaleas, but alittle rough on our trails. Be sure to wear sturdy shoes when you plan your visit. This will be the final installment of our Azalea Blossom Watch for this year.