Disease is the the major drawback to planting of American Elms. The elm is equally suseptible to Dutch Elm Disease, and Elm Yellows (or phloem necrosis). Ironically this tree was once overplanted to such an extent that it became a symbol for improvement of biodiversity in our cities, but now planting of elms can actually improve biodiversity in the urban forest canopy. Many elms continue to survive in urban settings today (see photo below)
A favorite on the "do not plant list", we forget that this tree is one of our most urban tolerant native trees. We often also forget that the greatest threat to a plant's survival may well be the urban site. We are often replacing trees in severe urban sites every five years; even disease sensitive American elms will last longer in these situations. Disease is realy the only drawback to planting elms in our cities. A simple sanitation program will yield a service life for American elm of twenty-five years. Today we have disease tolerant American elms available and they should live longer, and these should be considered for limited use in urban areas, especially in areas where elms previously thrived, but where other species are being replaced on a frequent basis.
Growth Characteristics
American elms can reach heights of 75-100 feet along streets, but their vase-shaped habit and natural pruning of lower branches will allow them to grow over powerlines with much less pruning than other trees such as maples. Elms tolerate heavy stresses such as soil compaction, salt, and poor drainage. When planting elms it is recommended that they be alternated with shade tolerant species from another family (such as sugar maples) to reduce root grafting which can transmit disease. Their vase shaped habits, and rapid growth rate will compete vigorously with other trees for light and root space. Fall color is good and fallen leaves are light and easy to collect.
Disease Resistance
Dutch Elm Disease tolerant cultivars include 'Valley Forge' and 'New Harmony', American elms that were introduced about five years ago from the National Arboretum. 'Princeton' American elm was introduced by Princeton Nursery around 1920 about ten years before DED was introduced. Its disease tolerance remained unknown until the 1990s, as everyone forgot about the reasons for growing American elm and concentrated on remembering why you should not grow the plant. Elms Tolerant of Dutch Elm disease have not been proven to be tolerant of Elm Yellows. cultural sanitation practices, and systemic fungicides such as Alamo® have been shown to be effective. Let us use the loss of this urban tolerant tree as a reminder of why we need diversity, and remember to plant a tree for what it can do.
