We all are mourning the loss of so many mature elms to Dutch Elm Disease
this year. Perhaps we can think of the situation as an opportunity. Most
of the large elms were planted in 1909 for a major festival, so they have
filled the space all that time. Some new trees that will grow quickly, that
are not susceptible to disease, and that will restore our lovely urban forest
are in order.
The first point to consider is that the stump and as much of the root ball
as possible should be removed or ground out. There will be considerable
settling for some time, especially for a large, old tree. Any new tree should
be planted at least 10’ away from where an elm was removed, and the soil
should have lots of compost added to make up for the nutrients used by the
elm.
When replacing a tree, it is wise to consider more than just the growth
rate. Is this tree known to develop surface roots? Is there room at the
site for both the roots and the canopy? Is an 80’ tree really necessary?
Larger trees that are not elms are many. If you are replacing a tree from
the boulevard, be sure to check with your city forester to see which varieties
are permitted.
Choose among the following
Some new varieties of Elm (see below) are resistant
to the disease, and can be planted as replacements.
The other varieties best suited are: River Birch 40’-60’ - dappled shade, moist soils Catalpa 40’-60’ - tolerates many sites, short-lived but spectacular Kentucky Coffee Tree 50’-60’ - native, good golden fall color Ginkgo 40’-60’ - tolerant of many harsh situations, golden leaves
drop in 12 hours in fall Hackberry 50’-75’ - native, tolerant of harsh sites, source of food
for many butterflies, needs careful pruning when young Honeylocust 30’-50’ - tolerates salt and drought American or Mongolian Linden (if you can get well away from the elm
roots), 30’-60’ Oak ‘Crimson Spire’, ‘Heritage’, ‘Regal Prince’ - each is a cross
with Quercus rober, the English Oak, 45’-80’, narrower, in general, than
our native oaks, and they grow faster, as well Yellowwood 25’-40’ - fragrant flowers, moist, well-drained soil
Or perhaps look at some of the smaller trees with flowers, fruit for the
birds, or great color in fall, such as Buckeye, Amur Cherry, Japanese Tree
Lilac, Maackia, Showy Mountain Ash, Prairie Gem pear, Serviceberry, Sour
Gum, Pagoda or Grey Dogwood, or Viburnum lentago.
New Elms
Several research groups have been working to develop elms resistant to Dutch
Elm Disease (DED). There has been some success. What follows is a much abbreviated
adaptation of an article out of Iowa State University. American Elm cultivars Valley Forge - best DED tolerance; upright arching,
vase-shaped form 26’ after 12 growing seasons, Zone 5 New Harmony - not as resistant as Valley Forge,
good shape 66’tall and 72’ wide Zone 4 Independence - good shape, DED tolerant, “quite
susceptible to elm yellows (a relatively rare disease in the Midwest)”
None of these are immune to DED and there are no mature trees yet to evaluate.
Asian/European contributions Accolade - good form, good resistance to DED, elm
leaf beetle, leaf miner less tolerant of urban and clay soils Cathedral - developed at the University of Wisconsin,
good form and disease resistance, Zone 4 Frontier - zone 5-6, pyramidal form, leaves first
red, then yellow-green, then purple Homestead - zone 5-6, pyramidal, susceptible to
elm leaf beetle New Horizon - high resistance to disease, upright
form, dense crown, Zone 4 Patriot - high disease resistance, good shape,
considered Zone 4 Pioneer - vigorous, very broad crown, Zone 5-8
Prospector - vase-shaped becoming pendulous. Zone 4-7
Regal - upright oval crown, no fall color, sparse
leaves (lighter shade) mean turf does better under this one, Zone 4
In each case, these trees are not identical to the glorious vase-shaped
American elm. The moral for all of us who love it, is that perhaps we loved
it a bit too much, and planted it so regularly that we left it no escape
once disease entered the picture.
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