Prairie Expedition™ Elm (Ulmus americana 'Lewis & Clark')

Prairie Expedition™ (cultivar name 'Lewis & Clark') is a pure American elm cultivar released by North Dakota State University. It combines high DED resistance with exceptional cold-hardiness, making it the leading resistant American elm option for USDA zones 3 and lower-4.

Origin

Prairie Expedition™ was developed by Dale Herman and colleagues at the North Dakota State University Department of Plant Sciences as part of the university's Woody Plant Improvement Program. The original tree was a survivor American elm growing in Fargo, North Dakota, that had remained healthy through multiple DED outbreaks in the region.

After extensive inoculation and field testing, the cultivar was released in 2004 under the trade name Prairie Expedition™, commemorating the bicentennial of the Lewis and Clark expedition through the northern plains.

Identification

• Form: Upright spreading vase shape, somewhat broader than 'Valley Forge'
• Mature size: 55–65 feet tall, 50–60 foot crown spread
• 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

Hardiness and adaptability

• USDA hardiness zones: 3–7 (exceptional cold-hardiness)
• Site preferences: Adaptable; performs well in cold-winter prairie conditions and continental climates
• Stress tolerance: Drought-tolerant; salt-tolerant; well-adapted to harsh prairie winters

Dutch Elm Disease resistance

Prairie Expedition™ shows high DED resistance. The cultivar has performed strongly in regional trials throughout the northern plains, where DED has been a major historical issue in cities like Winnipeg, Fargo, and Minneapolis.

Resistance is comparable to other top-tier American elm cultivars; the cultivar's distinguishing advantage is the combination of resistance with cold-hardiness extending into zone 3.

Landscape uses

• Street trees and park plantings throughout the northern United States and Canadian prairies
• Restoration of cold-region urban canopies decimated by DED
• Plantings in continental-climate cities where Accolade™ and other Asian hybrids are also marginally hardy
• Estate and farm shelter plantings in the northern Great Plains

Limitations

• Less widely available than southern-zone cultivars
• Like all American elms, susceptible to elm yellows (a phytoplasma disease distinct from DED)
• Production initially limited; availability expanded substantially after 2010

Similar cultivars

• 'Valley Forge' — higher resistance but less cold-hardy
• 'Discovery' — Japanese elm cultivar bred for prairie conditions
• 'New Harmony' — higher resistance but less cold-hardy

Related pages

• What Cultivars Are Resistant to Dutch Elm Disease?
• Disease-Resistant Varieties Guide
• American Elm (Ulmus americana)

References

• Herman, D. E., & Eisensmith, C. R. (2006). "'Lewis & Clark' American elm." HortScience, 41(3), 845–846.
• 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.
• North Dakota State University. NDSU Research Foundation cultivar release records.