Gentle giants – The American Elm Story
It is with a great deal of nostalgia and a heavy heart that we look back at the days when kids rode their bikes down streets lined with majestic American Elm Trees. Most of those gentle giants are gone now—victims of the dreaded Dutch Elm disease that hit our shores in the 1930s. The disease lingers on, continuing to threaten the survivors. But contrary to what many people think, there are Elm survivors, and where there are survivors there is hope. The last chapter hasn’t yet been written on our beloved American Elm. Here is the Great American Elm story!
The American Elm (Ulmus americana) is native from southern Canada to central Florida and from the Dakotas to the Atlantic Ocean. Its seedlings may be found all over this vast area even today. The Tree flourishes in the rich soil of riverbanks and tolerates periodical flooding, but the resilient Elm adapts to all sorts of growing conditions, which is one reason why it has made such a great street Tree. It can even handle salty soil, making it useful where de-icing salts are used.
You’ll recognize American Elm by its elliptical leaves with jagged margins that appear to have been cut with pinking shears. If you look closer, you’ll notice the ovals are lopsided, in typical Elm fashion. In fall, the foliage turns a rich, luminous golden yellow before dropping to reveal the Tree’s strong architecture.
The classic vase shape
You’ll also recognize American Elm by its architecture, but you might be surprised to learn that Elm doesn’t always take that iconic vase shape. Occasionally, it takes the “Oak Tree” shape, with powerful horizontal limbs, or the “Weeping Willow” shape, with graceful, long, slender branches that sweep the ground. Once in a while, an Elm seedling develops a “plume” shape, with a super-slim, vertical habit and a feathery tuft of foliage adorning the top.
Most often, though, American Elm is a classic vase, and this is what made many of our Elm-lined neighborhood streets so idyllic in days gone by. The trunks would stand, straight and stoic, rising free of limbs for 20 feet or more before splitting off into finer and finer branching high overhead. When planted on both sides of the street, the canopies would meet in the middle, forming a living arch and turning the space into an immense, open-air cathedral. On a sunny summer’s day, to walk in the dappled shade cast by the leafy ceiling high above was soothing—if not downright magical. We took this experience for granted until a nefarious fungus changed all that.
Dutch Elm disease strikes
Dutch Elm disease (Ophiostoma ulmi) arrived in Cleveland in 1930 as a stowaway in European Elm logs that were destined to be sliced into veneer to dress up fancy furniture. The logs housed both the devastating fungus as well as the Elm bark beetle, an insect which serves as an efficient vector to spread the disease from Tree to Tree. (Dutch Elm disease can also jump from one Tree to the next directly through the root system when the roots of two Trees naturally fuse or graft together.) To make matters worse, in the 1960s a more aggressive strain (Ophiostoma novo-ulmi) developed in the U.S. that was even harder to control. The disease along with the beetle marched through the country, killing the majority of the grand old American Elms it encountered in its path—some 77 million of them. Most of the destruction occurred during the 1940s through the 1970s.
Dutch Elm disease plugs up the vascular system of the Tree, and the first symptoms are the tips of single branches dying out. The leaves will wilt and turn yellow or brown, and they may fall prematurely. You may also see small holes in the bark where the beetles have emerged. Infected Trees often die within a year or two, although some hang on for several years.
Fighting and preventing Dutch Elm disease
Elm Trees that show the first signs of Dutch Elm disease can sometimes be saved by prompt removal of the diseased branches. Pruning must extend well into healthy wood, as the fungus can travel far beyond the point of infection in a short amount of time. Tools must be disinfected after each cut, and all infected wood should be cleared away and destroyed immediately.
To protect specimen Elm Trees that haven’t contracted Dutch Elm disease, it’s possible to inoculate them against infection. An arborist does this by injecting a fungicide directly into the root system on an annual basis. Treatment isn’t cheap, but in many cases it’s worth the expense if the Tree would be costly to remove or if it has immeasurable sentimental or aesthetic value.
Disease-resistant American Elm Trees
Some American Elm Trees have survived the onslaught of Dutch Elm disease with no protection whatsoever, other than their own natural resistance to the fungus. These Trees have caught the eye of nurserypeople, who have selected the best ones and tested them to see if they’re truly resistant. (Some mature Elms are still around simply because they’re growing in isolation from other Elms, and thus have not been exposed to the disease.) Elm researchers inject promising clones with high doses of the disease to determine if they can fight it off. Here are a few standouts:
The Princeton American Elm was selected as a superior shade Tree back in 1922 at Princeton Nurseries in New Jersey. Only much later was it realized that it happened to be very Dutch Elm disease resistant to boot. The original Tree did finally succumb to the disease, but not until it had reached the ripe old age of 278 years, which is exceedingly old for an Elm Tree. Princeton is a fast-growing Tree with that classic upright vase shape and radiant golden fall color.
Valley Forge has been the most Dutch-Elm-disease-resistant American Elm selection to date. It was introduced by the U.S. National Arboretum in 1995, after 20 years of diligent testing. As a tribute to its toughness, it was named ‘Valley Forge’ in reference to the tenacity of General George Washington and his troops during the brutal winter of 1777–78 at Valley Forge, Pennsylvania. This large Tree has the iconic, upright-arching Elm habit. It grows very quickly and may need a fair amount of pruning when young to keep it from getting unruly.
The New Harmony American Elm is also an extremely fast-growing Tree, though its shape is neater and more rounded than that of Valley Forge. It is also a National Arboretum introduction. It’s resistant to Dutch Elm disease, but not quite as resistant as Valley Forge or Princeton. New Harmony’s glossy, dark green leaves turn yellow in autumn.
The Prairie Expedition® (a.k.a. ‘Lewis & Clark’) American Elm is relatively new on the market and was named for the Lewis and Clark Expedition Bicentennial in 2004. Discovered in North Dakota, it has the added benefit of being extra cold hardy. This fast-growing Tree was the sole survivor of a Dutch Elm disease outbreak that killed all of the other American Elms around it. It takes on an umbrella shape and is clothed in lustrous deep green foliage that turns golden in the fall.
The American Elm lives on
We may no longer have streets lined with mighty American Elms, but this noble shade Tree is not merely a relic of the past. Some resilient specimens persist, and steps can be taken to keep them healthy. For new plantings, several selections of American Elm have emerged that boast a natural resistance to the Dutch Elm disease that wiped out so many Trees in the past. Battered but not defeated, this proud example of our natural heritage will live on for generations to come.