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 2009, the peak azalea bloom should be between April 20 and April 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

Today the Korean Rhododendron (Rhododendron mucronulatum) and hybrids using it as one of the parents are in full bloom. It blooms every year at the same time as forsythia. We are grateful for the recent rainfall after a fairly dry winter season. With this dry winter, we are noticing a lot of branch dieback due to winter injury. This is caused by winter sunlight and drying winds that cause desiccation (drying out) of the foliage and this in turn results in winter injury seen as brown patches on the leaves or entire branches of your evergreens. While some plants such as rhododendrons will put up new growth in the spring and hide the winter damage, other plants would prefer to have the winter damaged limbs removed by pruning.

At this time the bud formation on the azaleas is normal. That is, they are beginning to swell, and a few early blossoms are opening up along the ground line. By this time next week we should see much more color on the south side of the collection. The peak period of bloom should occur between April 20 and April 30 unless we have a sharp turn in temperature towards the freezing mark. The Magnolia Collection is in full spectacular bloom this weekend is a must-see.

April 9th

Today, several of the earliest Glenn Dales are showing their color. 'Festive', 'Allure', and 'Dayspring' are already showing opened flowers. The massed azalea hillside is ready to pop with color. Buds are showing color throughout the Azalea Collection. Many of our Weston hybrids are in bloom today. Selections such as ‘Llenroc’ and ‘Peach Blend’ and 'PJM' are full of opened blossoms right now. Adding their colors to the splendor, later-flowering Cherries, magnolias and daffodils have also just opened this week.

Worried about the effect the cool temperatures are having on your springtime azalea buds? Worry not. As long as our night time temperatures remain above 33 degrees F, your buds should be fine. If temperatures drop below freezing (32 degrees F), the buds may suffer and not bloom this year. We call this “bud-blast” and it will not harm the overall plant.

The cool weather we’ve been having this week has had the effect of halting the azalea bloom in its tracks. Today, there are expanding buds showing color all over the Azalea Collection with about 5% open. Give us a couple of warm, sunny days, and we should start seeing the collection open up-maybe by the weekend.

In bloom today are redbuds, late magnolias, late cherries, and many tulips are up. In the azalea collection is an unusual form of redbud in bloom, (Cercis canadensis var. albiflorum) which is white, located near the Frederic P. Lee Azalea Garden. Also in that area is a pinkish-lavender deciduous azalea, Rhododendron reticulatum, native to Japan but happily growing in the Lee Garden.

If you are able to make it to the garden this week, please excuse our mess as we are nearing the end of installing a brand new irrigation system into the collection. This is a much needed improvement. This week the Morrison Garden will be closed while work is being done.

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 we are seeing bud color and opened azalea blossoms throughout the collection today. The dogwoods are only just opening their showy white bracts. This year we may witness the rare phenomenon where the early and midseason azaleas are in full bloom at the same time. Dogwoods and daffodils, usually past at this time, will still be out in all their glory with the azaleas. This will only get better by the weekend.

In bloom today are the early Kurume azaleas and the early Glenn Dales, such as 'Dream', 'Allure', and 'Dayspring', which can be found in the Morrison Garden, as well as lilacs and redbud trees. We are nearing the end of the installation of our new irrigation system in the Azalea Collection. Signs will be posted where work is in progress causing minor detours but the collection will remain open.

Note also that this weekend the Friends of the National Arboretum (FONA) plant sale is being held on Saturday, so parking will be at a premium.

If you’re from the metropolitan area, you know we just emerged from a minor heat wave – very unusual for April. Temperatures between 80 and 90 degrees Fahrenheit for four straight days (Saturday through Tuesday) caused many an early bloomers to open and finish in just a few days. The azaleas, however seemed to weather the weather just fine. If there was any doubt about the peak bloom for azaleas before, there is no doubt now – it is right now.

The normally early Kurume hybrids have come into full bloom. Early and mid-season Glenn Dales are in bloom now. The Kurume azaleas have been used in American gardens for almost a century, while the Glenn Dales were hybridized by Benjamin Morrison, the first director of the National Arboretum, and introduced to the nursery trade by 1952. You will encounter the Kurume 'Ima Shojo' which is the same azalea as 'Hinode Giri' or 'Christmas Cheer' depending on its origins. The mid-season Glenn Dale 'Dauntless' is just opening up today with its deep purple blossoms. Many more Glenn Dales can be seen in the Morrison Garden.

Speckled amongst the lavenders, pinks, and reds are orange blossoms of one of our native azaleas, the Florida Flame Azalea, Rhododendron austrinum. Found in the uplands of Florida and into Georgia, this fragrant azalea grows perfectly well in our area. Most of what you see have been raised from seed, but we also have a few named cultivars bred for larger flowers or an unusual color. 'Aromi Sunrise', 'Millie Mac', and 'Variegated Austrinum' are among the selections of this native you will find in bloom in the azalea collections this week.

With many days of rain this weekend and still predicted for the next few days, the early azaleas have pretty much finished up their bloom cycle for the year. The mid-season bloomers such as the Glenn Dales 'Chanticleer', 'Morning Star', and 'Echo' are in full bloom along with many others.

Many of the deciduous azaleas are blooming now and loving this rain. This can be a good time to make your visit to the azaleas as the trails will be less crowded. Some deciduous azaleas to see now are Rhododendron atlanticum, the fragrant white Coast Azalea, and Rhododendron austrinum, the Florida Flame Azalea, which is still in full bloom with its many forms and shades of orange to yellow. Some interesting deciduous azaleas come from the University of Minnesota and are called The Northern Lights Group. We have 'Mandarin Lights', and 'Lemon Lights' among others. While these were selected for cold hardiness, they do very well here in our area. Like the Northern Lights Group, the Aromi Group of deciduous azaleas does very well in our area, but these were bred and selected in Alabama. 'Aromi Sunrise' and 'Sunny Side Up' are two very beautiful cultivars you will find in bloom this week.

The main display of azaleas in the collection have passed. Now the later bloomers are showing their colors. Come out and see the Glenn Dale 'Elizabeth', 'Pink Star' or 'Copperman' light up a lush green area of the garden. The entire Satsuki hybrid group is in full bloom now. Visit the Frederic P. Lee Azalea Garden and see over 100 Satsuki hybrid azaleas in bloom. For dense low growing ground cover types, the North Tisbury Hybrids have numerous late bloomers in their ranks and many of them grow no taller than 12 inches.

Rhododendrons and Mountain Laurels are well-represented in the Azalea Collections as well. Rhododendron cultivars are planted in and around the Lee Garden and mountain laurel (Kalmia latifolia) are located along the wooded edge facing the Flowering Tree Walk.

This will be our final installment of the 2009 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.