Slippery elm is an elm tree native to North America that grows throughout the United States and Canada in both dry and moist soils. The inner bark has a slippery texture that gives the tree its name. Though not often used in carpentry, the wood is fibrous and can be turned into excellent twine or rope. This species is susceptible to damage by the elm leaf beetle.
I. Appearance and Characteristics
Ulmus rubra, the slippery elm, is a species of elm native to eastern North America. Other common names include red elm, gray elm, soft elm, moose elm, and Indian elm.
The tree was first named as part of Ulmus americana in 1753, but identified as a separate species, U. rubra, in 1793 by Pennsylvania botanist Gotthilf Muhlenberg. The slightly later name U. fulva, published by French botanist André Michaux in 1803, is still widely used in information related to dietary supplements and alternative medicine.
Ulmus rubra is a medium-sized deciduous tree with a spreading head of branches, commonly growing to 12–19 meters (39–62 feet), very occasionally over 30 m (98 ft) in height. Its heartwood is reddish-brown.
The broad oblong to obovate leaves are 10–20 centimeters (4–8 inches) long, rough above but velvety below, with coarse double-serrate margins, acuminate apices and oblique bases; the petioles are 6–12 millimeters (1⁄4–15⁄32 in) long. The leaves are often tinged red on emergence, turning dark green by summer and a dull yellow in autumn.
The perfect, apetalous, wind-pollinated flowers are produced before the leaves in early spring, usually in tight, short-stalked, clusters of 10–20. The reddish-brown fruit is an oval winged samara, orbicular to obovate, slightly notched at the top, 12–18 mm (15⁄32–23⁄32 in) long, the single, central seed coated with red-brown hairs, naked elsewhere.
II. How to Grow and Care
Sunlight
For vigorous growth, full sun is preferred. If the tree does not receive enough light, it will grow slowly with slender branches that have a longer leaf spacing and a lighter leaf color. Summer is the most active growth season for slippery elm, making adequate sunlight essential at this time.
Temperature
plants of Genus Ulmus are mainly native to the temperate zone of the northern hemisphere. These trees are known for their adaptability – they enjoy adequate sunshine, but are also tolerant to cold and drought, with a developed root system that provides resistance to strong winds and soil erosion. The trees have a long lifespan and are usually fast growers, with strong vitality.
Watering
After planting slippery elm into a garden, water immediately, repeating 4 or 5 times after each watering has penetrated into the soil. Wait for a week before watering again, and then wait 20 days from planting before watering for the third time. After that, plants should be able to absorb enough water from the soil by themselves. Although water will need to be replenished in the morning and evening during especially hot periods, manual watering will not otherwise be needed.
In the case of bonsai, a thorough watering is generally required whenever the soil in the pot is dry. If the weather is dry and the temperature high, then more watering will be needed. However, never allow your plant to become water-logged. The best watering time is early morning or at night. In the winter, cut back on how much water you provide – your plant may not need any at all. Additionally, in order to avoid spindling or leaf enlargement, do not spray water on the leaves.
With good drought tolerance, watering should always be done according to the condition of the soil; if the soil isn’t dry, watering isn’t needed. Avoid water-logging or watering too frequently – this will cause an oxygen deficiency, leading to rotting roots and eventual plant death.
Soil
Slippery elm can tolerate a variety of different soil types and pH values, but good drainage is a must. Fertile sandy loam is best suited to the tree’s growth, and this can be mixed with garden soil, leaf mold and river sand at a ratio of 1:1:1 as cultivation soil.
Fertilizing
During the growth period of slippery elm in the warmer seasons, a diluted organic water-soluble fertilizer can be applied once a month. Fertilizing should be stopped after the plant goes into hibernation in the winter, but an organic fertilizer can be applied to the soil under the projection of the outer edge of the tree crown just before spring.
Planting Instructions
Seeds mature in the spring, with robust plants that are between 15 to 30 years old being best for harvesting seeds from. Air-dry the seeds, and then remove shells and impurities before sowing. It is best to sow the seeds directly after harvesting them, otherwise they will need to be stored in a well-sealed environment.
Place seedlings into fertile sandy loam with good drainage, and irrigate. Once the seedlings grow 2-3 leaflets, any weak seedlings should be removed, leaving 15 seedlings along a 1 m stretch of soil. In the seedling stage, scarification and weeding should be carried out regularly, and soil should be kept moist. The most vigorous growth period for seedlings is early summer, which is when plants should be topdressed every fortnight. The height of a 1-year-old seedling can reach more than 1 m, so ensure that you have adequate space.
Pruning
Prune slippery elm in the late winter to thin its branches and remove any that are diseased. This is also a good time to prune for tree shape. In the spring, once the branch buds sprout, you will need to remove any excessive lateral buds. Select the buds from the parts needed for cultivation to maintain the tree’s shape, as this will reduce unnecessary nutrition consumption.
Propagation
Slippery elm can be propagated by cuttings in the spring and fall. Choose strong branches that are more than 5 mm thick and cut them into lengths of between 15 to 20 cm long. Keep both the upper flat cut and the lower cut in a horse-ear shape. The planting distance should be around 20 cm, and only a small part of the branch needs to protrude from the ground. Cover the soil firmly and water it. The cutting will take about a month to root, so adequate irrigation is needed in order to promote survival during this period.
Transplanting
For slippery elm, autumn through spring (S1-S3) is the prime transplanting period. During these cooler months, it roots securely, prepping for vigorous growth. Choose locations rich in loam soil and partial to full sun. As a tip, always provide ample water post-transplant for a thriving slippery elm.
Pests and Diseases
The tree is reputedly less susceptible to Dutch elm disease than other species of American elms, but is severely damaged by the elm leaf beetle (Xanthogaleruca luteola).
III. Uses and Benefits
- Ornamental uses
Slippery elm is characterized by its large size and lush, fine-textured canopy that nearly reaches the ground. Although rarely employed in landscaping, it can still be used as a shade tree or to create hedges, screens, and windbreaks. Its tolerance of pollution and various environmental conditions make it an excellent tree for urban gardens and parks, given there is enough space to accommodate it.
- Medicinal uses
The species has various traditional medicinal uses. The inner bark has long been used as a demulcent, and is still produced commercially for this purpose in the United States with approval for sale as an over-the-counter demulcent by the US Food and Drug Administration. Sometimes the leaves are dried and ground into a powder, then made into a tea.
- Culinary uses
The mucilaginous inner bark of the tree is edible raw or boiled, and was eaten by Native Americans. The bark can also be used to make tea.
- Other uses
Timber
The timber is not of much importance commercially, and is not found anywhere in great quantity. Macoun considered it more durable than that of the other elms, and better suited for railway ties, fence-posts, and rails, while Pinchot recommended planting it in the Mississippi valley, as it grows fast in youth, and could be utilized for fence-posts when quite young, since the sapwood, if thoroughly dried, is quite as durable as the heartwood. The wood is also used for the hubs of wagon wheels, as it is very shock resistant owing to the interlocking grain. The wood, as ‘red elm’, is sometimes used to make bows for archery. The yoke of the Liberty Bell, a symbol of the independence of the United States, was made from slippery elm.
Baseball
Though now outmoded, slippery elm tablets were chewed by spitball pitchers to enhance the effectiveness of the saliva applied to make the pitched baseball curve. Gaylord Perry wrote about how he used slippery elm tablets in his 1974 autobiography, Me and the Spitter.
Miscellaneous
The tree’s fibrous inner bark produces a strong and durable fiber that can be spun into thread, twine, or rope useful for bowstrings, ropes, jewellery, clothing, snowshoe bindings, woven mats, and even some musical instruments. Once cured, the wood is also excellent for starting fires with the bow-drill method, as it grinds into a very fine flammable powder under friction.