American elm (Ulmus americana) is a deciduous hermaphroditic tree which can be found in a variety of habitats – swamps, low-lying lands, areas surrounding rivers, hillsides, and highlands. It was a very dominant tree species in North America before Dutch elm disease was introduced during the first half of the 20th century, which caused massive die-offs.
| Common name | American Elm, Common Elm, Gray Elm, Soft Elm, Water Elm, White Elm |
| Botanical name | Ulmus americana |
| Family | Ulmaceae |
| Species | americana |
| Origin | Eastern North America |
| Life cycle | Perennial |
| Plant type | Native Plant |
| Hardiness zone | 3, 4, 5, 6, 7, 8, 9 |
| Sunlight | Full Sun |
| Maintenance | Medium |
| Soil condition | Clay |
| Soil ph | Neutral |
| Drainage | Well-Drained |
| Growth rate | Fast |
| Spacing | more than 60 ft. |
| Harvest time | Spring |
| Flowering period | Winter |
| Height | 6- 80 ft. |
| Width | 6- 80 ft. |
| Flower color | Green |
| Leaf color | Green |
| Stem color | Brown, Copper |
| Fruit type | Samara |
| Garden style | Butterfly Garden |
| Uses | Naturalized Area |
I. Appearance and Characteristics
Ulmus americana, generally known as the American elm or, less commonly, as the white elm or water elm, is a species of elm native to eastern North America. The trees can live for several hundred years. It is a very hardy species that can withstand low winter temperatures, but it is affected by Dutch elm disease.
The wood was seldom utilized until the advent of mechanical sawing. It is the state tree of Massachusetts.
Ulmus americana was first described and named by Carl Linnaeus in his Species Plantarum, published in 1753. No subspecies or varieties are currently recognized.
The American elm is a deciduous monoecious tree which, before the introduction of Dutch elm disease (DED), commonly grew to more than 30 meters (100 feet) tall with a trunk whose diameter at breast height (dbh) was more than 1.2 m (4 ft), supporting a high, spreading umbrella-like canopy. The leaves are alternate, 7–20 centimeters (3–8 inches) long, with double-serrate margins and an oblique base. The leaves turn yellow in the fall.
The perfect flowers are small, purple-brown and, being wind-pollinated, apetalous. The flowers are also protogynous, the female parts maturing before the male, thus reducing, but not eliminating, self-fertilization, and emerge in early spring before the leaves. The fruit is a flat samara 2 cm (3⁄4 in) long by 1.5 cm broad, with a circular papery wing surrounding the single 4.5 millimeters (1⁄8 inch) seed. As in the closely related Ulmus laevis (European white elm), the flowers and seeds are borne on 1–3 cm long stems. American elm is wholly insensitive to daylight length (photoperiod), and will continue to grow well into autumn until injured by frost. Ploidy is 2n = 56, or more rarely, 2n = 28.
For over 80 years, U. americana had been identified as a tetraploid, i.e. having double the usual number of chromosomes, making it unique within the genus. However, a study published in 2011 by the Agricultural Research Service of the United States Department of Agriculture revealed that about 20% of wild American elms are diploid and may even constitute another species. Moreover, several triploid trees known only in cultivation, such as ‘Jefferson’, are possessed of a high degree of resistance to DED, which ravaged American elms in the 20th century. This suggests that the diploid parent trees, which have markedly smaller cells than the tetraploid, may too be highly resistant to the disease.
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 american 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 american 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
American 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 american 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 american 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
American 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
The best time to transplant american elm is from late spring to midsummer, as it allows ample time for the roots to establish before colder weather. Choose a location with well-drained soil and ample sunlight. For transplant success, ensure proper root ball handling and maintain adequate moisture during the initial growth phase.
Pests and Diseases
The American elm is susceptible to Dutch Elm Disease and to elm yellows. In North America, there are three species of elm bark beetles: one native, Hylurgopinus rufipes (“native elm bark beetle”); and two invasive, Scolytus multistriatus (“smaller European elm bark beetle”) and Scolytus schevyrewi (“banded elm bark beetle”). Although intensive feeding by elm bark beetles can kill weakened trees, their main impact is as vectors of DED.
American elm is also moderately preferred for feeding and reproduction by the adult elm leaf beetle Xanthogaleruca luteola and highly preferred for feeding by the Japanese beetle Popillia japonica in the United States.
U. americana is also the most susceptible of all the elms to verticillium wilt, whose external symptoms closely mimic those of DED. However, the condition is far less serious, and afflicted trees should recover the following year.
III. Uses and Benefits
- Garden Use
American elm is one of the most popular trees grown in the USA, in home gardens and public places, such as streets and parks. Its elegant style of growth — especially when planted near each other, creating an arching effect — and gorgeous autumn foliage make it extremely desirable as an ornamental and shade-providing tree. Hydrangeas, garden mums, and hicks yew work well as companions.
- Wood
The American elm’s wood is coarse, hard, and tough, with interlacing, contorted fibers that make it difficult to split or chop, and cause it to warp after sawing. Accordingly, the wood originally had few uses, save for making hubs for wagon wheels. Later, with the advent of mechanical sawing, American elm wood was used for barrel staves, trunk-slats, and hoop-poles, and subsequently became fundamental to the manufacture of wooden automobile bodies, with the intricate fibers holding screws unusually well.
- Pioneer and traditional uses
Young twigs and branches of the American elm have tough, fibrous bark that has been used as a tying and binding material, even for rope swings for children, and also for making whips.
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