July 20th, 2016
Also known as a White Elm, Water Elm, and Common Elm.
American Elms are long lived, usually growing to be about 18 – 24 metres tall and their crowns (the top of the tree with the leaves and branches) often have a spread of 9 - 18 metres. These trees have tall, straight trunks and multiple branches that start high up and grow into an umbrella or vase shape. The tree's bark is thick and rough, and usually dark grey to greyish-brown in colour with a distinctive diamond pattern on the trunk. The leaves are dark green and turn yellow in the fall. The edges of the leaves look jagged or toothed and the undersides of the leaves are rough.
American Elms are highly susceptible to Dutch Elm Disease (DED), a fatal disease caused by a fungus that is spread by a beetle. Alberta is fortunate to currently be Dutch Elm Disease free, but due to this disease, pruning of elms should only be done between October 1 and March 31, when the beetle that spreads the fungus is in its dormant stage. Visit the Alberta Agriculture and Forestry website [stopded.org] for more information on the disease.
Along with DED, elms can also suffer from aphids, borers, bark and leaf beetles, caterpillars, Japanese beetles, leaf hoppers, leaf miners, canker, leaf spot, or powdery mildew.
Best Care Practices
American Elms grow best in full sun to part shade. They prefer rich, well-drained soil but can grow well with poor drainage or compacted soil. If you notice that your elms' leaves are drooping during periods of very hot or dry weather, it may be time to give it some water. American Elms have large root systems, so it is best to water the whole area under the tree and even some of the surrounding ground, rather than watering just at the trunk.
Pruning is recommended every five to seven years to promote strong tree structure. Dead, dying, and diseased wood should be removed as soon as possible and as soon as allowed by local by-laws and legislation.
Interesting Facts about American Elm
- The City of Edmonton has one of the largest concentrations of DED-free American Elms in the world.
- A total of approximately 219,350 elms, worth around $634 million dollars, grow in Alberta's urban areas.
- American Elms are the largest species of elm.
- The Latin name is Ulmus americana.
- There was an American Elm in Ontario that was removed in 1968. It was discovered by counting the rings in its trunk that it had germinated in 1701.