Glenn Dale Azaleas
Notes on Slides Shown and Talk Given by Dr. Roy Magruder
Collaborator of the National Arboretum, Washington, D.C.
The National Arboretum is famous for its massed display of approximately 65,000 plants massed along the north side of the road on the South Slope of Mt. Hamilton. During the height of the blooming season (mid April to mid May) guides keep the traffic moving slowly along the back top road. There are foot paths throughout the display and a large parking area nearby for the use of those who wish to stroll among the flowers.
For those who wish to study the collection of Glenn Dale varieties in particular, they will park at the nearby Parking Area and enter the Morrison Garden by the entrance shown nearest the access road from the parking area. This garden is enclosed by a brick wall waist high. It has three lengthwise paths or walks and five cross walks forming 12 beds. The side beds around the perimeter contain 3 rows of plants (staggered) so each may be seen from the walks whereas the beds on each side of the middle walk contain 4 rows of plants each of which may be easily viewed by walking around the bed. Each plant has a variety name label. Most of them are Glenn Dales (usually only one of a variety) but the south end contains some Satsuki varieties.
At the North Exit from The Morrison Garden is another planting of Glenn Dale Azaleas on both sides of an elliptical walk, known as The Loop or The Azalea Loop. The Loop contains from one to three plants (usually contiguous) of a variety and each is labeled. Plants in this area have not been pruned so it is possible to observe the natural habit developed under partial shade and overhead irrigation. It also contains groups of varieties from other breeders and sources.
Chosen as an illustration of the double flowered type in the Glenn Dale is 'Delos' - a pink - the stamens have been proliferated into petals; also known as a rosebud azalea since the unopened flowers resemble rosebuds in shape. Other Glenn Dales in this group are 'Andros', 'Aries', 'Barchester', 'Kenwood', 'Ranger', and 'Rosette'.
Semi-doubles differ from doubles in that the stamens are only partially proliferated and the anthers appear on the edges of the inner petals. 'Aries' and 'Rosette' are reported as sometimes having both double and semi double flowers on the same plant. 'Firedance' and 'Modesty' are listed as semi-doubles. Still a double but not as formal as 'Delos'. is tawny rose 'Kenwood'.
Another flower type in the Glenn Dales is the hose-in-hose, of which solid white 'Damask' is a good example of the perfect hose-in-hose, where the five sepals have been transformed into petals indistinguishable from the upper layer. In irregular hose-in-hose varieties, the lower row segments (sepals) are irregular in form.
'Fashion' is a salmon rose hose-in-hose, very popular because of its dense growth, good retention of leaves through the winter, red fall foliage and bronze winter foliage. Prized by some and despised by others, hose-in-hose varieties do not shed the spent flowers cleanly - they dry brown and hang on for several weeks making an unsightly color in the border - as do the doubles and semi-doubles. There are 35 hose-in-hose Glenn Dale varieties of which 12 are irregularly hose-in-hose. Colors are white with stripes, solid pink, rose and salmon.
Among the singles, is a group of 16 varieties, with a white or almost white throat and a colored border on the petals. 'Martha Hitchcock' is probably the most widely distributed but varies in the amount of white in the throat sometimes absent on rapidly growing shoots. 'Boldface' also varies in the amount of white in the throat and in the sharpness of the colored border.
Another striking color pattern is found in the Glenn Dale varieties with colored throats and irregular white margins. 'Refrain' is a hose-in-hose type, white margins suffused Rosalane pink and with a few rose stripes, 1½-2 inches in diameter, and early blooming season. 'Surprise' is a mid May bloomer with a redder throat color and more striking blotch area than 'Refrain'. Other varieties in this color pattern are 'Helen Fox', 'Oriflamme', 'Nobility' and 'Valentine'.
Still another large (100 varieties) color pattern group is one where the color is primarily white with sanding. flecking, striping, sectors or selfs of either pink to Eugenia red or lavender, magenta or purple. 'Dimity' may be so heavily sanded and flecked as to appear pink from a distance - and also may have attractive Spinel pink self colored sports. 'Pinocchio' is another red marked variety with great variability in the amount of color in the flower. Three plants in the Arboretum Loop planting are all different. So don't buy one of these varieties except when in bloom - so you can see whether you like it. These are not recommended to nurserymen unless they do remove the selfs or other objectionable sports at blooming time as recommended in U. S. D. A. Monograph 20 or in The Azalea Book by F. P. Lee. 'Cavatina' is one of the lavender or magenta marked varieties in the variable or ever sporting group.
With the trend to smaller gardens we have been especially interested in the varieties that grow slowly, are compact and do not need pruning, retain enough foliage to be truly evergreen and have attractive summer, fall and winter foliage. 'Pearl Bradford' at the end of 11 yrs. in the Loop was 1824 inches high by 48 inches wide, on a sloping bank with full morning sun, good for the front of the border with excellent cover summer and winter, a late bloomer, deep rose pink but bud tender some years.
'Fawn' in fairly dense shade on a sloping bank was 20 x 60 inches, after 11 years, with dense cover, good retention of leaves, a mid-May bloomer, with white throat and mallow pink margin. 'Swanee' under a huge white oak but with 50% sun was 14 - 24 x 48 inches, irregular in outline but with dense cover and good retention, blooms in late April and is rose pink. 'F. C. Bradford', in full morning sun, was 38 x 48 inches with poor basal cover so it needs to be in the second row of the border. It has ascending branches, excellent dense tiers or shelf development, good retention of leaves and is a late April to early May bloomer; deep rose to rose red in masses over the tiers.
'Red Hussar' in fairly dense shade was 42 X 72 inches, had poor basal cover, open habit, poor leaf retention, blooms early (mid April), rose red color. Not recommended for small gardens.
'Swansong' in fairly dense shade was 28 - 30 X 86 inches with dense and twiggy cover, good retention, a mid May bloomer with heavy texture, large, solid white flowers. One of the best!
'Polar Sea' another very large solid white, frilled flowers blooming in mid May in fairly dense shade, was 30 X 60 inches in size with excellent leaf cover on the umbrella and fine tiers.
A tall, naked internode type of plant 72 X 72 inches in size and a rampant grower, is 'Treasure'. It is an early white (pale pink in bud), with heavier and darker leaves than 'Indica Alba', more retentive in winter. Too large for small gardens.
Another one not for small gardens because of large size and sprawling habit (84 X 84 inches) - is 'Kathleen', a mid to late May bloomer, medium rose in color.
Another undesirable trait - in 'Vespers' - is the production of long internode shoots that should be pruned back, on an otherwise desirable plant with well developed tiers bearing white flowers with occasional stripes of lavender.
More attention should be given to the selection of varieties of azaleas that will have colorful leaves in the fall and throughout the winter. The beautiful yellows, orange, red and maroons of fall actually provide longer periods of color than the flowers in the spring. 'Glacier' and all the other whites have bright yellow summer leaves until they turn brown in late November or December and fall off leaving green leaves near the ends of each new twig. Young plant grown in Washington area shows contrast between clear yellow and dark glossy green. 'Treasure' grown in dappled shade in Covington, Georgia, on November 4 shows the same coloration as 'Glacier'.
'Jubilant', an early purplish red grown at Covington, Georgia, is almost solid red (very little yellow or orange) in the fall.
'Sebastian' shows more orange leaves and maroon edges on the tip leaves when grown at Covington, Georgia. It is an early, rose, hose-in-hose Glenn Dale.
A fine spreading plant of 'Swashbuckler' also at Covington, Georgia has orange - red summer leaves and maroon tip leaves.
'Mayflower' grown in Stuart Armstrong's garden in Takoma Park, Md. had uniformly old-gold and light orange leaves.
'Campfire' grown at the National Arboretum and photographed about Thanksgiving time, had burgundy red summer leaves and maroon tip leaves.
'Daphnis', at the National Arboretum had lost most of its burgundy red summer leaves so the predominant color at Thanksgiving time was maroon and it will stay that color until the warmer weather of spring turns it green again.
Winter leaf color Kodachromes taken in the speaker's garden on Jan. 31, 1969 showed the flat all green leaves of 'Hexe', convex all green of 'Snowscape' and small, glossy solid maroon of 'Greeting'.
Another showed the solid bronze of 'Laity' and all green of a white variety.
The all green leaves of 'Helen Close' (white), 'Glacier' (white) and 'May Day' (a light salmon pink Chisholm-Merrett hybrid) illustrated that plants with green leaves do not always have white flowers, although all the azalea varieties I've observed with white flowers, have only yellow summer leaves and green winter leaves. There is good retention of small. light to medium green leaves on 'Dayspring' and a fine development of successive tiers characteristic of this variety.
Solid maroon color shows on Rhododendron carolinianum hybrid 'P.J.M.' and Glenn Dale azalea 'Anchorite' and grade 2 maroon (edges only) on Satsuki cultivar 'Hi Gasa'.