Plant of the Month - June, 2006

ARBORETUM PLANT OF THE MONTH FEATURE
by Jeff Iles
Arboretum Board Member

Professor and Chair
Department of Horticulture
Iowa State University

<P> Ulmus
'Morton'
(Accolade Elm)

Is it safe? You know, is it really safe to invite elms back into our landscapes? I must admit, whenever I recommend an elm selection for a residential or commercial property, my voice cracks just a bit, my palms get sweaty, and I have a little trouble maintaining eye contact with the client. It's not that I'm being dishonest or disingenuous. In fact, the elms I've recommended are part of a new and promising generation of disease resistant hybrid elms. I've even gone so far as to recommend a few true American elms that have demonstrated resistance to, or tolerance of the fungus causing Dutch elm disease. But no matter how hard I try, I simply can't erase the memory of that day in 1964 when the men with chainsaws came to remove every majestic, but now dead or dying American elm in my neighborhood. At first, the sound of screaming saws, cracking limbs, and stump grinders was exciting and entertaining, but as the trees disappeared, and the sun beat down on our street and houses for the first time in a very long time, it became painfully apparent our modest piece of suburbia had been transformed, and the transformation wasn't good.

So how wise are we to trust these "improved" elms? In other words, what guarantees do we have they won't succumb to some ravenous insect or super-virulent disease? Well, even with proven resistance to DED, we simply can't guarantee other problems won't come our way. But the same thing could be said for any tree species. Just look what's happening to our native ash in Michigan, Ohio, and Indiana. Who could have predicted the arrival and subsequent damage caused by the emerald ash borer? Therefore, the message is, many of these "new" elms are good landscape plants, but planting street upon street with the same cultivar or species is simply asking for trouble. Diversity remains the best hedge against unexpected and uninvited pests.

Okay, now that you're somewhat open to the idea of planting elms again, allow me to introduce you to Ulmus 'Morton' (Accolade™ elm). The original tree (dubbed the Thornhill elm) originated from seed collected at the Arnold Arboretum (near Boston, MA) in 1924, and over eighty years later the tree is still standing watch over the Thornhill Education Center at the Morton Arboretum. In fact, the elm improvement program led by Dr. George Ware (Dendrologist Emeritus) of the Morton Arboretum might never have gotten off the ground had it not been for this imposing specimen.

Ulmus 'Morton' (Accolade™ elm) is considered a hybrid between two Asian elms, Ulmus japonica (Japanese elm) and Ulmus wilsoniana (Wilson elm), but from a distance, the tree easily could pass for a venerable American elm. And if you planted Ulmus 'Morton' today, in approximately 20 years your tree would be 30' tall and 15' wide, eventually maturing into a classically vase-shaped elm, approximately 50-60' in height and spreading 30-40' wide.

In addition to its proven toughness and durability, and of course, resistance to Dutch elm disease, elm yellows, and elm leaf beetle, Ulmus 'Morton' (Accolade™ elm) has exquisite, dark green, glossy leaves that makes the foliage of most other shade trees appear ordinary and uninteresting by comparison.

Well, there you have it. I've told you what I believe to be the truth, and if you were in the room with me right now, I'd be speaking with a clear, strong voice and looking you square in the eye. But I hope you'd forgive me if I didn't shake your hand. You see, my palms are getting just a little sweaty.


About the author: Dr. Jeffery Iles presently serves as Professor and Chair of the Department of Horticulture at Iowa State University in Ames, Iowa. He holds advanced degrees from Penn State University and Iowa State University. Among many awards and honors, Dr. Iles is an Honorary Lifetime Member of the Iowa Nursery and Landscape Association. He has authored or co-authored more than twenty journal articles in such journals as HortTechnology, Journal of Environmental Horticulture, Journal of Arboriculture, and HortScience. Research projects Dr. Iles is currently involved in include Landscape Plant Evaluation, Invasive Landscape Plants, and Landscape Plant Usage. The Bickelhaupt Arboretum is fortunate to have Dr. Iles on its Board of Directors.