Common Name: American elm
Hardiness Zone: 3 to 9
Height: 60 to 100 ft
Width: 30 to 60 ft
Description: The American elm was widely planted throughout the United States and in the 1960's came under attack from Dutch Elm Disease. Millions of these trees were lost to Dutch Elm Disease. There are now disease resistant varieties being introduced to the market, but we recommend exercising caution when planting these and not to over-plant. The new varieties have been found to grow very fast and need a considerable amount of care and pruning when young. Included are descriptions, written by Chad Giblin, of some of the new varieties that are commercially available. This includes hybrid varieties as well.
1) Accolade Elm
This Morton Arboretum introduction has been a great selection for many years. This tree has a mature form that is similar to the American elm, but is slightly more upright and a bit smaller. Accolade™ has shown excellent performance in winter hardiness tests in the Twin Cities area, and generally outperforms many other varieties in terms of insect resistance as well. In 2004 we discovered two Accolade™ elms that had Dutch elm disease. While this is disconcerting, it was a good reminder of what the term resistant means; none of these selections are immune to DED. One of the two trees, currently under observation at the U of MN, currently has no symptoms of the disease and continues to grow with incredible vigor!
2) New Horizon Elm
The New Horizon elm is a product of a cross between U. pumila and U. japonica and is an introduction from the University of Wisconsin-Madison. It has many of the desirable features required for growth in the urban forest: fast growth, good insect resistance, and good DED resistance. In some cases co-dominant leaders and heavy side-branches can develop quickly on this variety, so higher levels of maintenance are required, especially in young trees. Like the Homestead elm, New Horizon appears to be favored by elm leaf beetle and has shown moderate feeding in our research plots.
3) Princeton Elm
Princeton is a true American elm that was actually selected for “superior horticultural qualities” prior to the DED epidemic (Stennes, 2003). This tree is slightly more upright than many of the seedling American elms around and it is this habit that requires much more attention to pruning during formative years as side branches develop quickly and may become included or dysfunctional very quickly. Outbreaks of Japanese beetles will result in heavy feeding on most young American elms, including Princeton and Valley Forge. Long-term effects of this feeding are currently unknown for our region. Other areas in the USA report recovery after a new flush of foliage. Princeton is not patented and can be legally propagated by anyone! In propagation studies at the U of MN, this tree is quite easy to clone using summer softwood cuttings. This tree received a lot of press coverage in 2007 and since has seen wider availability at a major home-improvement store locally. Like most American elms, young Princetons will require a heavy dose of structural pruning to establish good form.
4) St. Croix elm
Selected from a massive parent tree in Afton, MN, the ‘St. Croix’ American elm joins the ranks of Dutch elm disease-tolerant elms with a Minnesota twist. Since its discovery by U of M alumnus Mark Stennes, researchers in the Departments of Plant Pathology and Forest Resources have cloned and screened the tree for Dutch elm disease tolerance. Young specimens grow at an incredible pace and have gracefully arching branches and dark green leaves. Like all American elms, ‘St. Croix’ can thrive in tough environmental conditions.
5) Triumph Elm
Triumph™ is another new selection out of the Morton Arboretum in Illinois. Its parentage includes Vanguard™ and Accolade™. If you are looking for a tree with larger leaves than Accolade™, this might be the one! It has been relatively carefree in the nursery setting and has all the qualities of Accolade™ without many of the drawbacks like branch inclusion, breakage and so forth. However, it is reported to have less resistance to foliage feeders like the elm leaf beetle. This selection has also shown excellent performance on brownfield sites. Several have been growing in some of the worst sites in Minneapolis and Saint Paul for over ten years and show great promise for tough urban sites!
6) Valley Forge elm
Valley Forge is a true American elm introduction from U.S. National Arboretum with outstanding DED resistance. This tree has a lot of well-earned notoriety for being hard to manage in the nursery and as a young tree in the landscape! Once it gets into larger stem caliper ranges it seems to “settle down” a little and take on a more manageable form and habit. If you are interested in trying this tree, be ready to devote enough time to pruning it for long-term health and branch structure. Young Valley Forge (less than 10in DBH) should be pruned at least every two years for the first 10 to 12 years. It is reported to be 96% resistant to DED in inoculation studies and appears to be fully hardy in USDA Hardiness Zone 4. Also note susceptibility to Japanese beetle feeding, noted above under Princeton.