American elm (Ulmus americana) is a medium to large deciduous tree, typically growing to 60-80 feet tall with a vase-shaped, broad-rounded crown. It is native to eastern and central North America. Once widely planted as a street and lawn tree, its populations have been decimated by Dutch elm disease (DED) over the past century. Numerous pure-bred selections are being produced at nurseries. (List of Cultivars follows).

In landscape circles, American elm is recognized as the perfect shade tree to shade a home or backyard. This native tree has the classic vase-shape branching. Although cultivars may be selected for DED-resistance, they may still be at risk for other elm diseases, such as elm yellows and verticillium wilt. DED-resistance does not mean a cultivar is immune, but specific ones have significantly improved survival rates compared to seedling elms.

Insignificant small green flowers appear in spring before the foliage emerges. Flowers give way to single-seeded wafer-like samaras (each tiny seed is surrounded by a flattened oval-rounded papery wing). Seeds mature in April-May as the leaves reach full size. Rough-textured, ovate-elliptic, dark green leaves (to 6” long) have toothed margins and asymetrical bases. Leaves typically turn an undistinguished yellow in fall.

There are dozens of named cultivars of Ulmus americana. These are hybrid pure-blood selections.

‘Princeton’ was released by the Princeton Nursery in northern New Jersey in 1922 for its resistance to DED. demonstrates excellent resistance to DED. This variety is susceptible to phloem necrosis and wetwood. It is still planted in urban streets, parks, and on residential properties.

‘New Harmony’ was discovered in Ohio in 1922 and exhibits the old American Elm form and resistance to DED. Upright, vase-shaped tree with an arching form. Dark green leaves turn yellow in fall. Vigorous growing and slightly narrower than Valley Forge.

‘Valley Forge’, introduced by the U.S. National Arboretum, has the highest known DED resistance to date. Valley Forge’ seems to be more tolerant (96% resistant rate) of Dutch elm disease compared with ‘New Harmony’ (86% resistant rate). ‘Valley Forge’ demonstrates good cold hardness as far north as zone 4a.

‘Jefferson’ is a surviving clone found growing on the National Mall in Washington DC and introduced by the National Park Service. ‘Jefferson’ has excellent resistance to Dutch elm disease. However, the cultivar is susceptible to phloem necrosis, a disease that attacks the food-conducting tissue of the tree and susceptible to a bacterial disease called “Wetwood” that results in slow tree dieback.

Colonial Spirit® is another introduction from Princeton Nursery high DED resistance and has the classic American elm vase shaped branching habit. (65 feet high x 50 feet wide).

FYI — Hybrids of European and Chinese elms are Dutch Elm-resistant are available and grow shorter than American elms.