White (American) Elm
This is a beautiful tree that was once one of the most abundant trees in the North American landscape. However, with the introduction of the Dutch Elm disease (DED) the elm was almost wiped out of existence. From this tragic story comes hope – – the elm has a right to be in our landscape!
This is a tough, early succession, shade intolerant tree with an unmistakable form. In the forest, it forms a tall, straight trunk which rises to a considerable height before branching, but in the open like we are used to seeing now, it often divides near to the ground into several limbs which gradually form a fan shaped crown.
This tree has great wildlife value for birds – especially orioles. Orioles love the pendulous branches for nesting. Also, the spiny elm caterpillar prefers the elm and willow as its host (larval) food. Eventually, spiny elm caterpillars morph into the beautiful Mourning cloak butterfly.
The biggest problem facing the elm tree is that most elms in the wild are young trees living to about 20 – 30 years of age. They become sexually mature and then DED finds them and they die.
Dutch Elm disease arrived in North America in the 1930’s. By the 1950’s, outbreaks occurred until almost all the elms succumbed. This disease is actually a 2 phase system. The first phase involves the elm leaf beetle. They are now found everywhere in North America where ever elms grow. Larvae devour the lower surface of the leaves causing them to die and drop prematurely. Heavy defoliation weakens the trees and makes them subject to attacks by bark beetles and borers.
The second phase is the elm bark beetle. 2 kinds of bark beetles commonly attack elm trees in Canada and the US. One is our native elm bark beetle and the second is the European beetle. Today, both bark beetles are principal pests that spread the fungus to elms which results in DED. The disease interferes with the water transportation and stops nutrients from circulating within the tree.
I know, after reading about DED it makes you rethink your choice to plant this majestic tree. Do not be afraid to plant this tree. There is natural resistance in the population where 1 in 100,000 will survive. Because of this natural resistance, there is a massive recovery program happening in the United States and Canada where disease resistant elm are now being offered for sale to the general public and in reforestation projects.
Elms can be planted in a variety of soil conditions from fertile soils to drier, poorer sites. Since elm will grow and thrive on hotter, drier, drained sites – why not plant elms on these sites and save the richer, fertile areas for trees with more specific needs?
Because the elm can grow in poor conditions – it makes a great urban tree. We still need to plant with caution and wisdom. Do not be scared to plant the elm – it is a tree that deserves a chance. The expected life span of these disease resistant trees is estimated at 80 -135 years. But who really knows? – we are in uncharted area.
Our recommendations for planting are NO MASS PLANTINGS. Limit plantings to 3 – 5 trees per area. Very important – space trees over 50 feet apart to avoid root grafting. Large trees within 50 feet of one another are likely to have roots cross over in the soil and eventually fuse. The DED fungus can move from infected tree to adjacent tree through these root grafts. This root graft was a very significant cause of tree death in urban areas where trees were planted too closely together.
- full sun
- dry, drained, poorer soils
- space at least 50 feet apart
- 3 – 5 trees per site. No mass plantings.