Valley Forge Elm (Ulmus americana 'Valley Forge')

'Valley Forge' is a pure American elm cultivar released by the USDA National Arboretum in 1995. It is among the most DED-resistant American elm cultivars commercially available and is widely used in urban canopy restoration where a return to the classic American elm form is desired.

Origin

'Valley Forge' is a pure Ulmus americana selection. It descends from a survivor tree identified during a large-scale screening program at the National Arboretum led by USDA plant pathologist Alden Townsend. The program subjected hundreds of American elm selections to repeated inoculation challenges with virulent Ophiostoma novo-ulmi strains and advanced only the most resistant individuals through successive trial rounds.

After more than 20 years of screening, 'Valley Forge' was released alongside 'New Harmony' in 1995. The two have remained the benchmark for pure American elm resistance and serve as parents and reference standards for ongoing breeding programs.

Identification

  • Form: Classic American elm vase shape — single trunk dividing into upright spreading scaffold branches
  • Mature size: 60–70 feet tall, 50–70 foot spread at maturity
  • Leaves: Standard Ulmus americana foliage — 3–5 inch oval, double-serrated, asymmetric base, dark green
  • Bark: Light gray, deeply furrowed at maturity
  • Growth rate: Fast (2–3 feet per year)

Hardiness and adaptability

  • USDA hardiness zones: 4–9
  • Site preferences: Adaptable to most soils; tolerates urban conditions, compaction, and moderate flooding
  • Stress tolerance: Drought-tolerant once established; relatively salt-tolerant

Dutch Elm Disease resistance

'Valley Forge' shows exceptional resistance to DED. In USDA inoculation trials it demonstrated minimal vascular discoloration and high survival following challenge with virulent Ophiostoma novo-ulmi. Townsend et al. (2005) reported survival rates above 85% in artificially inoculated trees, among the highest in the screening program.

Field performance over the past three decades has supported the trial results. The cultivar is widely regarded as the most reliably DED-resistant pure American elm in commercial production.

Landscape uses

  • Street trees in cities restoring traditional American elm canopies
  • Large estate and park plantings
  • Restoration of historic elm-lined avenues
  • Mixed cultivar plantings to maintain genetic diversity within the resistant pool

Limitations

  • Form is somewhat irregular when young; the mature vase shape develops over 15–25 years
  • Like all American elms, susceptible to elm yellows, a phytoplasma disease distinct from DED
  • Requires structural pruning during early establishment
  • Production was limited initially; availability improved substantially after 2005

Similar cultivars

  • 'New Harmony' — USDA companion release, similarly high resistance
  • 'Princeton' — older selection, moderate-to-good resistance
  • 'Jefferson' — hexaploid American elm with high resistance

Related pages

References

  • Townsend, A. M., Bentz, S. E., & Douglass, L. W. (2005). "Evaluation of 19 American elm clones for tolerance to Dutch elm disease." Journal of Environmental Horticulture, 23(1), 21–24.
  • Townsend, A. M., & Douglass, L. W. (2001). "Variation among American elm clones in long-term dieback, growth, and survival following Ophiostoma inoculation." Journal of Environmental Horticulture, 19(2), 100–103.
  • Griffin, J. J., Jacobi, W. R., McPherson, E. G., et al. (2017). "Ten-year performance of the United States National Elm Trial." Arboriculture & Urban Forestry, 43(3), 107–120.