The

American Elm ''Ulmus americana'', generally known as the American elm or, less commonly, as the white elm or water elm, is a species of elm native to eastern North America. The trees can live for several hundred years. It is a very hardy species that can ...

cultivar A cultivar is a kind of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and which retains those traits when Plant propagation, propagated. Methods used to propagate cultivars include division, root a ...

''Ulmus americana'' 'Valley Forge' was raised by the

Agricultural Research Service The Agricultural Research Service (ARS) is the principal in-house research agency of the United States Department of Agriculture (USDA). ARS is one of four agencies in USDA's Research, Education and Economics mission area. ARS is charged with ext ...

Maryland Maryland ( ) is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. It borders the states of Virginia to its south, West Virginia to its west, Pennsylvania to its north, and Delaware to its east ...

. The tree was released to wholesale nurseries without patent restrictions by the U. S. National Arboretum in 1995 after proving to have a high resistance to Dutch elm disease. 'Valley Forge' proved only moderately successful in the US National Elm Trial, averaging a survival rate of 66.7% overall, owing largely to environmental factors rather than susceptibility to disease.

Description

The branching is typically upright and arching, creating a broad vase-shaped structure complemented by a dense canopy of leaves. However, Michael A. Dirr, Professor of Horticulture at the

University of Georgia The University of Georgia (UGA or Georgia) is a Public university, public Land-grant university, land-grant research university with its main campus in Athens, Georgia, United States. Chartered in 1785, it is the oldest public university in th ...

criticized the tree's form as 'floppy'. The bark features greyish, flat-topped ridges, separated by roughly diamond-shaped fissures. The dark green leaves are large, < 17 cm (avg. 12 cm) long by < 10 cm (avg. 7.4 cm) broad, typical of the species, turning golden yellow in autumn. In an assessment at U C Davis as part of the National Elm Trial, the tree initially grew comparatively slowly, increasing in height by 0.85 m per annum, although stem development at 2.6 cm d.b.h. was near average.McPherson, G. et al. (2008). National elm trial: Initial report from Northern California. ''Western Arborist'', Fall 2009, 32–36. Image: Valley Forge leaf and Euro coin.jpg, Leaf with 1 Euro coin Image: Valley forge autumn colour 2.jpg, Fall color

Pests and diseases

'Valley Forge' has proven the most resistant of all the American Elm cultivars (although it is not immune) to Dutch elm disease. While also very resistant to the elm leaf beetle, ''

Xanthogaleruca luteola ''Xanthogaleruca luteola'', commonly known as the elm-leaf beetle, is a beetle species in the family Chrysomelidae that is native to Europe but invasive in other parts of the world.http://cisr.ucr.edu/elm_leaf_beetle.html - Center for Invasive ...

'

like all other American Elms it is susceptible to Elm Yellows.Townsend, A. M., Bentz, S. E., and Douglass L. W. (2005)
Evaluation of 19 American Elm Clones for Tolerance to Dutch Elm Disease
. ''Journal of Environmental Horticulture'', March 2005, Horticultural Research Institute, Washington, D.C. In

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

'Valley Forge' has also been found to be susceptible to leaf curling

aphids Aphids are small sap-sucking insects in the Taxonomic rank, family Aphididae. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white Eriosomatinae, woolly ...

('' Eriosoma'' sp.) which produce honeydew The cultivar is only moderately preferred for feeding by the Japanese Beetle '' Popillia japonica'',Brady, C., Condra, J., & Potter, D. (2008) Resistance of Landscape-suitable Elm (Ulmus spp.) Cultivars to Japanese Beetle, Leaf Miners, and Gall Makers. ''2008 Research Report, Nursery & Landscape Program'', 15–16. University of Kentucky. but the species as a whole is the most susceptible of all the elms to

verticillium wilt Verticillium wilt is a wilt disease affecting over 350 species of eudicot plants. It is caused by six species of '' Verticillium'' fungi: ''V. dahliae'', ''V. albo-atrum'', ''V. longisporum'', ''V. nubilum'', ''V. theobr ...

.Pegg, G. F. & Brady, B. L. (2002). ''Verticillium Wilts''. CABI Publishing. In England, the leaves of 'Valley Forge,' along with those of other American Elm cultivars, remained completely free from Black Spot.Brookes, A. H. (2020). ''Great Fontley Elm Trial, 2020 Report''. Butterfly Conservation, Lulworth, England.

Cultivation

All examples included in 10-year trials at Atherton,

, to evaluate replacements for Californian elms lost to disease were withdrawn after a combination of rapid growth and poor structure condemned the trees as "likely to require more maintenance than most municipalities would find acceptable".Costello, L. R. (2004). A 10-year evaluation of the performance of four elm cultivars in California, U. S. ''Journal of Arboriculture'', March 2004

However, these verdicts may reflect in large measure the fact that they were grown in warm climates but with minimal weed competition. Trees raised in the nursery of the

University of Minnesota The University of Minnesota Twin Cities (historically known as University of Minnesota) is a public university, public Land-grant university, land-grant research university in the Minneapolis–Saint Paul, Twin Cities of Minneapolis and Saint ...

also proved very difficult to manage, but "settled down" as they matured, adopting a more manageable form and habit.Giblin, C. P. & Gillman, J. H. (2006). ''Elms for the Twin Cities: A Guide for Selection and Maintenance.'' University of Minnesota. 'Valley Forge' seems to develop far fewer structural problems in temperate climates further north, where the rate of growth in any given season is much more moderate. Moreover, where grown in the countryside, competing vegetation tends to keep excessively vigorous growth in chec

Interim results from the aforementioned trial at U C Davis confirm the tree's high pruning requirement. 'Valley Forge' was introduced to the UK in 2010; it is not known to have been introduced to

Australasia Australasia is a subregion of Oceania, comprising Australia, New Zealand (overlapping with Polynesia), and sometimes including New Guinea and surrounding islands (overlapping with Melanesia). The term is used in a number of different context ...

Etymology

'Valley Forge' was named for the site near

Philadelphia Philadelphia ( ), colloquially referred to as Philly, is the List of municipalities in Pennsylvania, most populous city in the U.S. state of Pennsylvania and the List of United States cities by population, sixth-most populous city in the Unit ...

where Washington's forces endured the winter of 1777 during the

War of Independence Wars of national liberation, also called wars of independence or wars of liberation, are conflicts fought by nations to gain independence. The term is used in conjunction with wars against foreign powers (or at least those perceived as foreign) ...

Accessions

;North America *

Arnold Arboretum The Arnold Arboretum is a botanical research institution and free public park affiliated with Harvard University and located in the Jamaica Plain and Roslindale, Massachusetts, Roslindale neighborhoods of Boston. Established in 1872, it is the ...

, US. Acc. no. 180-2003. *Bartlett Tree Expert

US. Acc. nos. 2001-258, 2001-259, 2001-486, 2001-491, 2003-1010. *

Brenton Arboretum The Brenton Arboretum is a 141-acre arboretum and public garden in Dallas Center, Iowa, United States, established in 1997. The arboretum displays 175 native Iowa trees and shrubs suitable to the site, as well as many other tree species which c ...

, Dallas Center,

Iowa Iowa ( ) is a U.S. state, state in the upper Midwestern United States, Midwestern region of the United States. It borders the Mississippi River to the east and the Missouri River and Big Sioux River to the west; Wisconsin to the northeast, Ill ...

, US. No details available. *

Dawes Arboretum The Dawes Arboretum is a nonprofit arboretum located in Newark, Ohio. It includes nearly of plant collections, gardens and natural areas. The site includes approximately 12 miles (19 km) of hiking trails and roadways for a four-mile (6&nb ...

br>
Newark, Ohio, Newark,

Ohio Ohio ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the ...

, US. 2 trees. No acc. details available. * Holden Arboretum, US. Acc. nos. 2002-76, 2004–38, 2004-47. *

Morton Arboretum The Morton Arboretum, in Lisle, Illinois, United States, is a public garden and outdoor museum with a library, herbarium, and program in tree research including the Center for Tree Science. Its grounds, covering 1,700 acres (6.9 square kilometre ...

, US. Acc. no. 127-2008, 268-2008, 214-2012. * Scott Arboretum, US. Acc. no. 98-110. *

Smith College Smith College is a Private university, private Liberal arts colleges in the United States, liberal arts Women's colleges in the United States, women's college in Northampton, Massachusetts, United States. It was chartered in 1871 by Sophia Smit ...

, US. Acc. no. 36205. *

University of Idaho The University of Idaho (U of I, or UIdaho) is a public land-grant research university in Moscow, Idaho, United States. Established in 1889 and opened three years later, it was the state's sole university for 71 years, until 1963. The un ...

Arboretum, US. Acc. no. 2004171. * U S National Arboretumbr>

Washington, D.C. Washington, D.C., formally the District of Columbia and commonly known as Washington or D.C., is the capital city and federal district of the United States. The city is on the Potomac River, across from Virginia, and shares land borders with ...

, US. Acc. nos. 76510, 68983.

Europe

Grange Farm Arboretum The Grange Farm Arboretum is a small private arboretum comprising 3 hectares accommodating over 800 trees, mostly native and ornamental species or cultivars, notably oaks, ashes, walnuts and elms, growing on a calcareous loam.Ostler, J. (2009) ...

, Sutton St James, Spalding,

Lincolnshire Lincolnshire (), abbreviated ''Lincs'', is a Ceremonial counties of England, ceremonial county in the East Midlands and Yorkshire and the Humber regions of England. It is bordered by the East Riding of Yorkshire across the Humber estuary to th ...

, UK. Whips planted 2011. Acc. no. 1056 *Great Fontley,

Fareham Fareham ( ) is a market town at the north-west tip of Portsmouth Harbour, between the cities of Portsmouth and Southampton in south east Hampshire, England. It gives its name to the Borough of Fareham. It was historically an important manufac ...

, UK, ''

Butterfly Conservation Butterfly Conservation (BC) is a UK-wide nonprofit environmentalist organization and charity dedicated to conserving butterflies, moths, and the environment. The charity uses its research to provide advice on how to conserve and restore butterf ...

'' Elm trials plantation, Home Field, two whips planted 2010. * Sir Harold Hillier Gardens, Ampfield,

Hampshire Hampshire (, ; abbreviated to Hants.) is a Ceremonial counties of England, ceremonial county in South East England. It is bordered by Berkshire to the north, Surrey and West Sussex to the east, the Isle of Wight across the Solent to the south, ...

, UK. One planted 2010. Acc. no. 2010.0383 * Wijdemeren city council, The Netherlands, Elm collection, two planted 2016, Rading 1, Loosdrecht.

Nurseries

Europe

*Van Den Berk (UK) Ltd.

London, UK

References

External links

*http://www.extension.iastate.edu/Publications/SUL4.pdf Summary, inc. photographs, of elm cultivars resistant to Dutch elm disease available in the United States.
Saving the American Elm, by Bruce Carley
*http://www.sunshinenursery.com/elms.htm Review of current elm selections in the United States. {{Elm species, varieties, hybrids, hybrid cultivars and species cultivars , state=collapsed American elm cultivar Ulmus articles with images Ulmus