Posts tagged ‘American elm’
Smithsonian Gardens manages the health and maintenance of 1,873 trees in the Washington, D.C. area. As you walk around the Smithsonian gardens and museums you may notice a common theme: many of these trees are mature specimens with historical context and connection to the museums they surround. This is extremely evident as you walk the grounds of the National Museum of Natural History, where the extensive American elm plantings bring us back to a time when Ulmus americana was the predominant street tree in America. In fact, the large specimen on the corner of 9th Street and Constitution Avenue predates the museum, which celebrated its centennial in 2010.
As Dutch Elm Disease (DED) has wiped out the majority of stately American elms throughout the U.S., we at Smithsonian Gardens work diligently to monitor and manage our trees in order to prevent the spread of this lethal disease.
It is with this management strategy in mind that we carefully select replacements when elm trees at the Smithsonian need to be removed. When one of the younger elms on the north lawn of the National Museum of Natural History was critically damaged during a storm, we once again debated and discussed which “resistant” elm to replace it with. One of the best choices for a true Ulmus americana replacement is the ‘Jefferson’ Elm (Ulmus americana ‘Jefferson’), selected through the collaborative efforts of the National Park Service and the USDA’s Agricultural Research Service (ARS).
This tree was selected for its excellent DED resistance and the fact that as a true species, it exhibits the classic American elm form, unlike some of the resistant hybrids.
‘Jefferson’ elms leaf out earlier in the spring and maintain their green color better in the summer than other U. americana specimens. We were very lucky to receive this tree from the National Park Service as it is just becoming available in the commercial trade at this time, and can be difficult to find. The National Park Service propagates ‘Jefferson’ by cuttings from the original tree, located on the National Mall, and grows the seedlings for six years at its National Capital Region Nursery. It is a long process and a difficult one, as only about 5% of the cuttings live to become mature trees. Hopefully this selection will become more common in the nursery trade so that we can once again plant these majestic trees with confidence. Until that time, we are very thankful for the ongoing collaboration between the National Park Service and Smithsonian Gardens to ensure that the American elm still graces the Washington, D.C. landscape.
-Jonathan Kavalier, Smithsonian Gardens Supervisory Horticulturist
As parents, teachers, and students wrap up the first couple of months of the new school year. Smithsonian Gardens horticulturist Christine Price-Abelow thought it would be fun to highlight a few plants with names linked to education. Keep an eye out for these plants growing in the museum gardens on your next class field trip!
1. Chinese Scholar-tree (Sophora japonica)
Chinese Scholar-tree is also known as the Japanese Pagodatree. In its native country of China the Scholar–tree was often planted near Buddhist shrines, hence the name. However it is commonly used as a city or street tree in the United States. It has a moderate to fast growth rate and usually reaches a height of 40-60’ with a nice rounded crown. Sophora trees have a compound leaf which casts a light shade and they are very tolerant to heat, drought and pollution. They produce creamy white flowers in mid-July followed by a pod type fruit. This “educational” tree can be found on the west side of the National Air and Space Museum near the McDonald’s trailer and seating area.
2. Princeton Elm (Ulmus americana ‘Princeton’)
The next time you visit Smithsonian Gardens and the National Mall, be sure to look up at the large towering trees shading the walkways. A large percentage of this tree canopy is made up of American elms, specifically the ‘Princeton’ American Elm. As you know, most plant cultivars are named for people and places and the ever popular Princeton elm is no exception. The Princeton elm was first introduced in 1922 by William Flemer of Princeton Nurseries located near Princeton, New Jersey. The Princeton elm was originally selected for its resistance to Dutch elm disease and aesthetic beauty. There are many examples of the Princeton elm planted throughout the U.S. and they can be genetically linked to a 200+ year old American elm tree formerly growing at Princeton Cemetery near Princeton University.
American elms have a beautiful yellow fall color and make excellent shade trees. They are fast growing and reach a height of about 80’ with a spread of 50-60’. The Princeton cultivar is known for its disease resistance and large dark green leaves. They are also a great choice for urban landscapes. Plant your own piece of history!
Smithsonian Gardens is using Ulmus Americana ‘Princeton’ as a street tree and in the tree box planters surrounding the museums.
3. Pencil Cactus (Euphorbia tirucalli)
In keeping with our “Back to School” theme, our next featured plant is the pencil cactus. Though often referred to as a cactus, this plant is actually a succulent and a member of the Euphorbia family. The pencil cactus is native to Africa and India, therefore it is grown as a seasonal tropical plant or a houseplant in the Washington, D.C. area. This euphorbia’s distinctive round, rod-shaped branches that resemble the familiar school implement give the plant its nickname. They are very easy to grow and can be propagated by cuttings.
*A note of caution, you should always wear gloves when working around this plant; it exudes a milky, latex-type sap that can cause an allergic skin reaction for some people.
This plant can be found growing in a large container in the Ripley Garden.
-Christine Abelow-Price, Smithsonian Gardens Horticulturist