Prize Plants From the U.S. National
Theyre adding a new viburnum cultivar to the list of award winners
that have been bred at the U.S. National Arboretum.
Released in 1988, Viburnum x burkwoodii Conoy was recently
selected as a 1997 winner of the Gold Medal Award by the Pennsylvania
Horticultural Society. This annual award honors new and little known trees,
shrubs, and vines of exceptional garden merit.
The awards purpose is to promote superior plants with the
public, growers, and retailers, says Kathleen A. Mills, who is manager of
the program. We look at how hardy the plant is, especially if its
not picky about the environment. Since 1988, the first year the society
made the awards, 56 plants have been honored as Gold Medal Award winners
Conoy is a dense, low-spreading, compact viburnum that grows to 5 feet with
a 7-foot spread. Its very glossy, fine-textured, evergreen leaves are dark
green in summer and reminiscent of boxwood. In extreme cold, the leaves turn
maroon or slightly bronze; in milder climates, they do not change. "Severe
cold has caused no winter injury in over 17 years of testing," says
arboretum horticulturist Ruth L. Dix.
"Unlike many large viburnums, Conoy is suitable for mass plantings, as
a specimen plant, for hedges, or in containers. And unlike most viburnums, it
can be pruned or sheared without looking like a barbershop reject," she
Conoy blooms in April with slightly fragrant, creamy-white flowers that
appear with the young leaves. A profusion of glossy, dark red fruit follows by
mid-August; they turn black in October. Resistant to bacterial leaf spot, Conoy
has withstood temperatures of -23°C and is hardy to USDA Plant Hardiness
Conoy is considered to be one of the best viburnum cultivars introduced by
the arboretum and the first that is completely evergreen in the Washington,
D.C., area. It grows best in a heavy loam soil with a pH of 6 to 6.5, partial
to full sun, and an adequate moisture supply.
Arboretum director Thomas S. Elias says that Conoy is the ninth arboretum
introduction named a Gold Medal Award winner and the fifth viburnum
introduction chosen for this award.
Managed by USDAs Agricultural Research Service, the arboretum was
established by Congress about 70 years ago on 444 acres in northeast
Washington, D.C. Since then, its researchers have developed more than 650 new
varieties of trees, shrubs, ground covers, and floral crops that today
landscape Americas streets, yards, and gardens.By Hank Becker,
R. Pooler is in the USDA-ARS Floral and Nursery Plants Research Unit, U.S.
National Arboretum, Washington, DC 20002-1958; phone (202) 245-4568.
The Egolf Legacy
During his 30 years of research at the arboretum, ARS
horticulturist Donald R. Egolf bred, tested, and released an astonishing number
of ornamental shrubs, including all five Gold Medal Award-winning viburnums.
All told, 19 of his viburnums, 27 crape myrtles, 6 pyracanthas, and 4
rose-of-Sharons were released by the arboretum before his death in 1990.
ARS geneticist Margaret R. Pooler, who was recently hired to continue
Egolf's research, says, "He was known throughout the horticultural world
for his high standards of quality and excellence of his cultivars. His
contribution to the nursery industry and the American public will be felt for
years to come."
Horticulturist Ruth L. Dix, who worked with Egolf as a student from 1978 to
1981 and as a support scientist from 1986 to 1990, agrees. "Many of these
cultivars have become the industry standardlike Pyracantha Mohave and
some of the viburnums, like Shasta," she says.
According to arboretum director Thomas S. Elias, "Besides Conoy, Egolf
introduced Shasta, Eskimo, Mohawk, and Eriefour other Gold Medal Award
winners, along with the hibiscus Diana."
Previous Gold Medal Winners
- 1993Viburnum x burkwoodii Mohawk. In late April, abundant,
bright-redbuds open to white petals with red blotches on undersides. Compact
growth habit, reaching 7 feet with a 7-foot spread. Very resistant to powdery
mildew and bacterial leaf spot. Hardy to USDA Plant Hardiness Zone 5b.
Deutzia gracillis Nikko.
- 1993Viburnum dilatatum Erie. A large, deciduous shrub with an
upright, shrubby growth habit, it reaches 6 feet with a width of 11 feet.
Medium-green leaves turn red, orange, and yellow in the fall before dropping.
Flowers are creamy-white in 4- to 6-inch-wide, flat-topped clusters opening in
mid-May. Pest- and disease-resistant. Zones 5 to 7.
- 1992Viburnum Eskimo. Handsome, snowball-flowered viburnum
grows 4-feet tall by 5 feet wide and has glossy, dark-green, semi-evergreen
leaves. In early to mid-May, masses of 3-inch, ball-shaped flowers composed of
pale-cream, tubular florets appear. Zones 6 through 8.
- 1992Magnolia Galaxy. A single-trunked, upright tree with a
narrow crown, appropriate as a street or landscape tree. Profuse, slightly
fragrant, dark-pink flowers open late enough in spring to avoid frost. At
maturity, 30 to 40 feet tall with superior heat tolerance. Zones 6 through 9.
- 1991Viburnum plicatum f. tomentosum ShastaWithout equal
for flowering, its abundant creamy-white flower clusters cover the upper sides
of horizontal branches in double rows 4 to 6 inches wide. Low growing. Zones 5
- 1991Hibiscus syriacus Diana. Its abundant 6-inch, waxy,
heavy-textured, pure-white, single flowers bloom from July until frost.
Tolerates a variety of soil types; prefers full sun. Can be cut back yearly to
2 feet to maintain a blooming height of 4 feet. Sets relatively few fruits and
seeds. Zones 5 to 8.
- 1989Deutzia gracilis Nikko. An excellent ground cover or low
shrub that grows to 2 feet with a spread of 5 feet. Sports small, pure-white
flowers in late April to early May and fine-textured, willowlike leaves that
turn deep burgundy in autumn. Zones 5 to 8.
- 1988Ilex Sparkleberry. A large, multistemmed, deciduous holly
with aprofusion of large, bright-red fruit. In fall, golden-yellow foliage
contrasts with ripening fruit that persists until spring. Grows to 12 feet with
a 12-foot spread. Zones 5b to 9.
The Route to Release
"Although arboretum plant introductions are not directly available for
general sales and distribution, we do make a major effort to make them
available to all nurseries wishing to grow them," says Ramon L. Jordan. He
leads studies in the Floral and Nursery Plants Research Unit at the Beltsville
(Maryland) Agricultural Research Center.
After we select and evaluate potential new cultivars, ARS distributes
them for evaluation by cooperating growers in other U.S. geographic
regions, he says. Plants are then named and released to cooperating
wholesale nurseries, where they are propagated for sale. New cultivars are also
distributed to cooperating arboretums, botanical gardens, and research