Succession planting of disease resistant Princeton elm, 2003.
American Elm Restoration
For more than half a century, the National Arboretums' Senior Plant Genetisist, Dr. Alden Townsend has rigorously tested 50,000 American elms for natural DED resistance. Though not immune, moderate to very high resistant cultivars such as New Harmony, Valley Forge and Princeton are now commercially available. The Jefferson, selected by the National Park Service from the mall in Washington D.C is also a reliable American elm cultivar for elm restoration. It displays a broad canopy with wide u-shaped branch structure which provides greater strength.
Of the dozens of elm cultivars available, many are propagated from Asian or European elms. These non-American elms may have excellent DED resistance. However, crown size and shape will vary. Accolade shows classic form with very high resistance, though mature size maybe smaller than the American elms.
Longevity of these cultivars is enhanced with proper sanitation practices and good tree-care maintenance, including early pruning and training to create a dominant leader and better branch structure.
Please see the slide provided to Elm Watch by Dr. Alden Townsend illustrating the culmination of some 50 years of testing of American elm cultivars and their resistance to Dutch Elm Disease (DED).
Please download the "Elm Restoration Report" form to help evaluate and document the process of siting, ownership, approvals, etc. for new plantings of Community trees.
How to plant your elm
To site and plant your American elm, think long and large. You are planting a hundred year tree, maybe a hundred fifty year tree if you do it right and favorable conditions prevail. The average life of street trees is seven to fourteen years. This is the result of insufficient site preparations, casual planting practices, and inadequate tree maintenance. The elm restoration form and checklist will help you think through the siting and planting process.
Soil conditions for most roadside and public tree sites consists of miscellaneous fill, various debris, and little topsoil. Planting setback from the roadside is generally more root friendly, lawns are better yet, but often can be improved with soil augmentation.
Early childhood development is as important to trees as to humans. Realize that ninety percent of feeder roots are severed when trees are spade dug. Container trees often have roots binding against the container wall. These are best cut away if they cannot be teased out of their entanglement, and should be pointed away from the tree trunk when setting the root ball.
Planting a tree is an investment. The best dollars spent are on planting pit preparations. Soils support root growth, root growth supports tree growth. The following procedures have resulted in the doubling of tree size in five years. For example, a relatively inexpensive 1½ inch caliper container elm, 12 feet tall becomes a 3-4 inch tree, 24 feet tall with a value of a thousand dollars.
Planting pits should be sized to accommodate large root zone development, even if planting a small tree. We recommend a minimum of three times the diameter of the root ball. A six to eight foot diameter pit is desirable to a depth of 24-36 inches, depending on the height of the root ball. Excavate existing fill and subsoils to the proper depth. Fill the planting pit with quality topsoil (eight to ten percent organic content is optimal.) Soil supplements such as peat moss will increase moisture retention and enhance root growth, however peat moss must be thoroughly mixed with soils. Adding Mycorrhiza may assist in nutrient assimilation by new root hairs.
Planting too deep is the number one cause of transplant tree loss. Measure root ball height first, recheck hole depth and place root ball to reveal trunk flare several inches above surrounding grade. Augmented soils in planting pit will settle several inches and therefore should be mounded above surrounding grade. Create a 4-6 inch dike just beyond outer root ball to retain water. A watering program is essential the first year and very desirable for three years.
Mulch 3-4 inches deep with waste wood chips. These will decompose and serve as an inexpensive means to feed your tree over time. Mulch needs to be replenished every 2-3 years. Bark chips add little nutrient content to the soil. Mulch helps retain soil moisture, helps reduce soil compaction and trunk damage by weed trimmers and lawn mowers. Expanding the mulch diameter (8, 10, 12 feet) as the trees grows will encourage more rapid root zone expansion.
Where to buy an elm tree
Visit Bruce Carley's website http://www.elmpost.org for a list of various online elm sales.