Ulmus pumila - Elm

Ulmus pumila, or Siberian Elm, is a deciduous tree with rapid growth commonly planted in cities. It is a good shade tree, with its slender trunk and rather erect and irregular vegetation, giving it a slightly disorderly appearance, which is very natural in aspect. Its small toothed leaves are light green in spring, darken in summer, and turn yellow in autumn before falling. Very hardy, it can withstand periods of drought. Of medium to large size, it is significantly taller than wide, making it suitable for medium-sized gardens. Rather resistant to Dutch elm disease, it can occasionally be attacked by insects. It can tolerate ordinary, neutral to calcareous, moist but well-drained soil.

Ulmus pumila belongs to the Ulmaceae family, like Southern Hackberry (Celtis) or Zelkova (false Siberian Elm), with which it should not be confused. It is native to Asia, from eastern Siberia to Korea, Mongolia and northern China. It was introduced to the United States in the early 20th century to combat wind erosion and has since naturalised there. In its native lands, it can reach a height of 25m (82ft), form a trunk with a diameter of 1m (3ft), and live up to 150 years.

Cultivated in temperate climates, Ulmus pumila rarely exceeds the age of 60 and a height of 15 to 20m (49 to 66ft). It has a more or less oval habit, with an irregular, slightly rounded or even slightly spreading crown, reaching a spread of about 8m (26ft). This makes it suitable for planting in large hedges, as its width is only half its height. It forms a bare trunk at the base, with upright, almost vertical, main branches. It branches out somewhat haphazardly. It is therefore advisable to prune it in the early years to shape it, while accepting its unruly appearance inherent in its genes, which gives it a natural silhouette. After all, it is a botanical species, not a horticultural variety! The grey bark is punctuated here and there with white patches; it is interesting, rather than decorative.

The leaves are slightly asymmetrical and small, ranging from 2 to 8cm (1 to 3in) long and 1.2 to 3.5cm (1in) wide, and the lamina has regular dentation. Carried by short petioles less than 1cm (1in) long, they are light green when they appear in spring and then darken, turning yellow in autumn before falling.

The flowers are petal-less and appear on the previous year's branches. Green in colour, they have no ornamental value and can be destroyed by frost when they form as early as February. Paradoxically, the tree itself is extremely hardy, tolerating temperatures as low as -35°C (-31°F). For this reason, it is highly appreciated in Canada, especially as it withstands the use of de-icing salt. The fruits are dry, brown samaras containing a central seed. They are produced abundantly.

This elm has many advantages and presents a number of drawbacks. It performs very well in urban conditions, resisting pollution and tolerating compacted and paved surfaces. Although it prefers moist and well-drained soil, it tolerates drought well and accepts poor soils. Growing in ordinary soils, it also tolerates very alkaline soils. Finally, it is generally resistant to Dutch elm disease, a disease that has devastated populations of this tree. However, the tree is susceptible to powdery mildew and canker, two fungal diseases, as well as a number of insects. It will only thrive in full sun, requiring a lot of light. Its wood is quite brittle and its crown tends to host dead branches over time.

Ulmus pumila will especially appeal to lovers of natural gardens, who are not attracted to sometimes overly sophisticated horticultural varieties. It will blend well with other plants in the same spirit, particularly in distinctly chalky soils. The male Cornelian Cherry (Cornus mas), a species that combines a beautiful early yellow flowering season, decorative red fruits, and interesting autumn colours, can be planted alongside it. In the same spirit, Amelanchier lamarckii will be a perfect companion, offering a magnificent white spring flowering, followed by edible dark fruits, which take on a sumptuous red colour in autumn.