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Princeton Elm

princeton elm ulmus americana ftimg

Princeton Elm

Ulmus americana ‘Princeton’

Description & Overview

Princeton Elm is an American Elm selected for its vigorous, upright symmetrical habit. Its large, dark green foliage forms a dense canopy turning yellow in fall. Tolerant of urban conditions and highly resistant to Dutch elm disease, Princeton Elm is an excellent component of street tree plantings or for sites with poor soil conditions.


Core Characteristics

Wisconsin Native: No – Variety of North American Native
Mature Height: 60-80 feet
Mature Spread: 40-60 feet
Growth Rate: Fast
Growth Form: Upright, symmetrical
Light Requirements: Full Sun to Partial Shade
Site Requirements: Tolerant of many sites but use caution in exceptionally dry areas
Flower: Insignificant, small 3-4 flowered clusters on 1 inch pedicels
Bloom Period: April
Foliage: Dark Green
Fall Color: Yellow
Fruit Notes: Small wafer, light green-tan, mostly self-sterile

Suggested Uses:

Princeton Elm makes an excellent street tree, shade tree, or accent in the landscape. Although it prefers full sun, it can grow in partial-shade areas receiving 4-6 hours of direct light per day. All elms, including Princeton Elm, are not resistant to Verticillium Wilt and should not be used to replace trees killed by the fungus.

princeton elm ulmus americana branching leaf structure

Wildlife Value:

The branch crotches of Princeton Elm provide habitat for many migrant bird species. The tree also hosts a plethora of insects that no doubt provide a buffet for insectivores. When seeds are produced, Princeton Elm will provide food for birds and small mammals.

Princeton Elm, as a cultivar of American Elm, can serve as a larval host to the Eastern Comma, Mourning Cloak, Question Mark, and Painted Lady butterflies. And if you’re lucky, you may spot the massive Columbia Silkmoth caterpillar.

Maintenance Tips:

Dutch Elm Disease is spread by three species of bark beetle in the United States (two in Wisconsin). When trees are damaged, they release compounds that signal other trees to prepare for the same sort of injury. However, these bark beetles have also evolved to “sniff out” these injured trees and attack them, bringing Dutch Elm Disease along for the ride.

For this reason, Princeton Elm (and all other elms) should be pruned only during the dormant season when the beetles are inactive and the trees are not releasing the warning signal compounds. The only time that pruning during the active season should be accepted is when there is significant risk posed by the branch to be pruned. A certified arborist will be able to provide more information for your situation if necessary. To find one, visit the Wisconsin Arborist Association Arborist for Hire page to locate one near you.

While Elms are tough trees- and Princeton Elm is no exception- you should avoid stressing them as much as possible. Watering during periods of drought, using a large mulch ring of 2-2.5 inches in depth, and avoiding other insect damage during the growing season will reduce the chances of your Princeton Elm developing Dutch Elm Disease.

If you are concerned that your Princeton Elm may have developed Dutch Elm Disease, contact your local arborist to assess your tree and develop a plant health care program. Treatment for this disease is technical and requires products not available to the homeowner.

Young, thin-barked trees should be protected during the winter months from buck rub with a vinyl tree guard or similar product. Trunk damage will reduce tree vigor, cause canopy dieback, and will open the tree to future infection by other diseases.

Pests/Problems:

No Elm cultivar is completely immune to Dutch Elm Disease, and even highly resistant cultivars like Princeton Elm can fall victim to the fungus when stressed. Watering during drought, mulching, and avoiding mechanical damage (including pruning) during the growing season will help reduce the chance of the tree developing Dutch Elm Disease.

Princeton Elm has excellent resistance to Dutch Elm Disease but is susceptible to other diseases and insects when stressed. You can greatly reduce your chances of acquiring these diseases by keeping your tree healthy and vigorous. They include:

  • Elm Phloem Necrosis, also called Elm Yellows, is a fatal disease with symptoms similar to Dutch Elm Disease. It is caused by a phytoplasma and is spread by a leafhopper insect. Symptoms include yellowing leaves followed by branch death. There is no treatment for this disease and most infected trees die within three years. Infected trees should be removed as soon as possible to prevent the disease from spreading, but the good news is that Elm Phloem Necrosis is not as virulent as Dutch Elm Disease.
  • Princeton Elm is somewhat resistant to Elm Leaf Beetle, which will defoliate portions of the tree. This insect can have dramatic fluctuations in population between years, so some years will have high levels of damage while others will be barely noticeable. If you observe damage to your Princeton Elm’s foliage, be careful to not confuse Elm Leaf Beetle’s chewing marks with the early signs of Dutch Elm Disease. If you are unsure of the source of this damage, contact a certified arborist. Because of this tree’s significance as a larval host for several butterfly species, insecticides should be used judiciously and only when needed.
  • Leaf Blister (Taphrina), Black Spot (Stegophora ulmea), and Powdery Mildew are other leaf problems that can occur when weather and pest conditions are right. These diseases are rarely fatal and are relatively easy to control with good cultural practices, like destroying fallen leaves at the end of the season. Consider these problems the ‘common cold’ of elm trees that are easily remedied by keeping the tree healthy. In the worst infestations, spraying may be beneficial. If you believe your tree is in need of professional help, contact a certified arborist.
  • Princeton Elm is not resistant to Verticillium Wilt and should not be planted where the disease has been observed in the past. This fungal pathogen will persist in soil and there is no treatment. If your Princeton Elm develops Verticillium Wilt, you must select a resistant species as a replacement and avoid using susceptible trees in your landscape in future plantings.
  • Of lesser concern is Bacterial Wetwood and Slime Flux, which cause discolored bark and have an oozing appearance. This is caused by, you guessed it, bacteria that infects the stem tissue, builds up pressure, and creates a bleeding discoloration that is most noticeable around wounds and branch crotches. While this condition is not fatal, it is unsightly and there is no cure. You can prevent this issue by avoiding wounding the tree’s above- and below-ground tissues.

Leaf Lore:

Princeton Elm was selected by William Flemer of Princeton Nurseries in 1922 for its graceful upright habit and attractive branching. Oddly enough, it also had good resistance to Dutch Elm Disease (DED), although this was not known until Princeton Elm was tested in the 1990’s by the USDA. It is the only American Elm (Ulmus americana) cultivar that has been grown to maturity despite the presence of Dutch Elm Disease. Some of these trees can be seen at the now-defunct Princeton Nurseries, planted in the 1920s and lining several allees. Princeton Elm was selected from a tree growing in Princeton Cemetery, which was felled in 2005 after suffering significant dieback. While the original tree is gone, it lives on in the Princeton Elms that line many municipal streets across the United States– including a certain stretch of Pennsylvania Avenue in Washington, D.C.

The leaves of American Elm and its cultivars decay rapidly when compared to other hardwoods like Oaks, Maples, and Hickory. They are also high in nutrient content. For these reasons and its rapid growth, American Elm is useful as a soil-building plant where soils are depleted or generally poor.

American Elm and its cultivars are generally self-sterile. While individual trees can produce fruit, they are rarely viable. If fruit production is a concern, plant American Elm cultivars like Princeton Elm individually to avoid cross pollination.

The wood of American Elm and its cultivars has interlocking grains. This makes it tolerant of flexing and bending while retaining strength, but also makes splitting firewood from American Elm either horrendously difficult or a great workout- depending on your perspective. Elm wood is used for hockey sticks, furniture, and flooring, and was used to make food storage crates due to its odorless nature.

Companion Plants:

The upright, vase-like habit of Princeton Elm contrasts well with lower, rounded trees like Corneliancherry Dogwood, J.N. Strain Musclewood, and Eastern Redbud. For shrubs and perennials, consider using shade-tolerant spreaders like Running Serviceberry, Thriller Lady’s Mantle, or Palace Purple Coralbells.


Princeton Elm Ulmus americana Princeton benchcard

PRINCETON ELM BENCHCARD