By Len Phillips, ASLA Emeritus
Photos provided by J. Frank Schmidt & Son Co.The Society of Municipal Arborists has chosen Accolade™, a hybrid selection of Japanese elm, Ulmus japonica x Wilson elm, U. wilsoniana as its 2012 Urban Tree of the Year. The Society of Municipal Arborists conducts the Urban Tree of the Year competition every year to illustrate the importance of selecting the right tree for the right spot. The intent of this program is not to indicate that this is the perfect tree that can grow anywhere, but is to make arborists aware of this tree, and they should use it if they have a site suitable for it. The Urban Tree of the Year also provides extra publicity to excellent trees that need planting more often. Our cities often contain too many of the common maples and ash that are cheap, easy to grow and are short-lived. A quality urban tree is a better investment for the future of the city and the urban forest.
Accolade is a hybrid elm with an attractive, upright spreading habit and shiny leaves that provide good fall color. Plus it is resistant to Dutch elm disease; is reminiscent of the American Elm, U. Americana; is excellent as a street tree or a shade tree for larger landscapes; and is very adaptable to adverse site conditions. Accolade is an introduction from The Morton Arboretum near Chicago, and introduced through the Chicagoland Grows Plant Introduction Program.
Size and features
Accolade will grow to be about 50 to 60 feet tall at maturity, with a spread of 30 to 40 feet. The tree does not grow as large as the American elm. It has a high canopy with a typical clearance of 7 feet from the ground, and it should not be planted underneath power lines. The tree grows vigorously at first, gaining as much as 3 feet per year, but slows to less than half that rate with maturity.
The original tree at The Morton Arboretum is noted for its resemblance to the American elm, its upright-arching branches creating the familiar vase-shape. Accolade has dark-green, glossy leaves that turn gold colored in the fall. The bark, flowers and fruit have no ornamental value.
Genetics and development
Accolade began at The Morton Arboretum from open pollinated seed of Japanese and Wilson elms received from the Arnold Arboretum in 1924. It was selected for its Dutch elm disease resistance, the vase-shaped form, vigorous growth, excellent drought tolerance, and good strong yellow fall color. Accolade is available from many local garden centers and nurseries.
Accolade grows best in USDA Hardiness Zones 4 – 8. It is slightly less hardy than the American elm and won’t grow to be as tall or intimidating, but this may actually be an advantage in terms of general home landscape use.
In artificial freezing tests at The Morton Arboretum, the LT50 (temp. at which 50% of tissues die) Accolade was found to meet the – 32 °F (- 35.5 °C) level.
Pest and disease resistance
Accolade has excellent disease resistance to both elm yellows and Dutch elm disease. The original tree, in its 80-plus years, has survived three epidemics of Dutch elm disease unscathed. Two trees included in trials at the University of Minnesota were found to be afflicted by the disease in 2004, but recovered completely. It has also proved to be highly resistant to the elm leaf beetle Xanthogaleruca luteola, but not to the Japanese beetle, Popillia japonica. It is currently being evaluated in a National Elm Trial coordinated by Colorado State University.
Accolade begins flowering after 8 years of age. Under ideal conditions it can be expected to live for 90 years or more. This tree performs best in full sun. It is very adaptable to both dry and moist locations, and should do just fine under average home landscape conditions. It tolerates most soil types and pH values, and it is able to handle environmental salt. It will not tolerate extremely wet soils.
The tree is commercially propagated by tissue culture and by grafting onto U. pumila rootstock.
Like all new hybrid elm selections, Accolade develops the best structure with pruning every couple of years during its youth. Prune the tree so trunks and branches will not rub each other. Remove secondary branches with included bark at the main branches. This reduces the likelihood of the main branch splitting from the tree later when it has grown to become an important part of the landscape. Locate the tree properly, taking into account the ultimate size, since the tree looks best if it is not pruned to control its size.
The wood is considered ring-porous which means that there is a large difference in size between the spring wood pores and the summer wood pores. Elms are among those susceptible to summer branch drop according to surveys in California. Summer branch drop is a phenomena resulting in failure and breakage of large-diameter, live branches, typically on calm summer days. All elms reportedly produce allergenic pollen.
It is a relatively low-maintenance tree. It has no significant negative characteristics. It is highly tolerant of urban pollution, and will even thrive in inner city environments. Accolade roots can break sidewalks and raise pavement if the trees are not properly located.
Many of us remember the stately elm lined streets of the past and this tree brings back that elegance, while offering the disease resistance that will provide a healthy tree for generations to come. Accolade is an extremely tough, fast-growing tree that has a distinctly native look and feel. This tree is sure to satisfy and reminds us all why nearly every town in America has an Elm Street.
Len Phillips can be reached via email at firstname.lastname@example.org.
Editor’s Note: Arbor Age magazine and author Len Phillips have no role in the selection of the Urban Tree of the Year, and are merely reporting this year’s selection, as well as supporting details and observations about the selection, here.
Special thanks to Keith Warren from J. Frank Schmidt & Son and Kris Bachtell from The Morton Arboretum.
“Accolade, Ulmus ‘Morton’”, Nature Hills Nursery, Inc., Omaha, NE, 2011.
Chicagoland Grows®, Inc., Accolade, Plant Introduction Program, Plant Release Bulletin #11, 2002.
“Handsome new hybrid elm answers need for tough shade tree”, J. Frank Schmidt & Son Nursery, 2011.
Northscaping, “Ulmus Accolade,” “Northscaping.com, 2011.
Urban Tree of the Year at a Glance
Botanical Name: Ulmus ‘Morton’
Trade Name: Accolade™
Parentage: U. japonica x U. wilsoniana
Year of Seed Development: 1924
Year of Introduction: 1996
Height: 50 to 60
Spread: 30 to 40
Form: Upright spreading habit
Bloom Period: March
Fruit: Round samara
Summer Foliage: Dark green in summer
Autumn Foliage: Bright gold in autumn
Winter Color: Bark provides winter interest
Bark: Furrowed gray bark
Habitat: Tolerates most soils, pH, and environmental salt
Culture: Prefers rich, moist soil
Hardiness Zone*: 5 – 8
Growth Rate: Fast, more than 3 feet per year in youth; 45 feet in 20 years
Pest Resistance: Resistant to Dutch elm disease and elm yellows, highly resistant to the elm leaf beetle
Storm Resistance: Good
Salt Resistance: Tolerant
Planting: Easily transplanted bare root or B&B, suitable for use in CU-Structural Soil, quickly recovers from transplanting
Pruning: Prune in late winter after the threat of extreme cold has passed
Propagating: Own roots with tissue culture and by grafting onto U. pumila rootstock
Design Uses: Good for homes, streets, parks, and commercial landscapes
Companions: Looks good with most general landscape plants
Other Comments: Fast growing tree which has a distinctly native look
Available: Most large nurseries
* For information about the USDA Hardiness Zone Map, visit www.usna.usda.gov/Hardzone/index.html