The first elm to earn the name ‘Jefferson’ is on the National Mall near the Freer and Sackler Galleries. It stands out for its shape — it has the traditional vase shape, but with a more rounded crown than the typical American Elm — and its color — it is a darker green. It also leafs out earlier and holds its leaves longer. Those are desirable traits, but more significantly, it has shown resistance to Dutch elm disease (DED).
The ‘Jefferson’ elm was previously thought to be a hybrid of the Ulmus americana and another species. However, scientists from the National Arboretum have determined the ‘Jefferson’ elm on the National Mall is a true varietal of the species instead of a hybrid. Planted in the 1930s, the original specimen had survived DED.
However, if you were to purchase a ‘Jefferson’ — and they are just becoming available commercially — your elm would be a clone of that elm on the Mall. That is the only way to assure that you would be getting the same genetic makeup — the disease-resistance, color and shape characteristics so prized in the original. The first clones were made in 1993 and are just now becoming available commercially. Small ‘Jefferson’ elms in one quart or one gallon containers are selling for $25 and $40 at the Botany Shop Garden Center in Joplin, Missouri. By contrast, a three foot tall ‘Princeton’ elm, a disease-resistant cultivar, can be purchased for $12.
I had the privilege of taking a tour of the National Mall’s elm trees with Jim Sherald, a plant pathologist with the National Park Service’s Center for Urban Ecology who helped test the ‘Jefferson’ for DED resistance. He showed how the ‘Jefferson,’ clearly a favorite of his, stands out among the many elms of the Mall. Take the test yourself this spring.