Ulmus

Family: Ulmaceae
Common Name: Elm

There are over 40 species in this genus of hand-some, deciduous trees, from temperate regions of the northern hemisphere. They make lovely shade trees, although the larger species are usuÂally only suitable for large gardens and parks, as their roots are fairly invasive. The toothed leaves are asymmetrical at the base, with prominent lateral veins, those of most species colouring yellow in tall. Both the inconspicuous flowers and the winged fruits are borne in clusters.

Species

U. americana, American elm, zone 2, from North America, is a majestic tree, growing to 40 m (130 ft) in the wild, but much smaller in cultivation. It has a rounded crown and a trunk covered with deeply fissured, gray bark. The leaves are 15 cm (6 in) long. This species yields fine timber, but it is now nearly extinct in its habitat. There are several cultivars.

U. glabra, wych elm or Scotch elm, zone 5, is not often grown now. This species can grow as tall as 35 m (115 ft), and has large, rough, oval leaves, to 15 cm (6 in) long. This is a non-suckÂering species. Cultivar 'Lutescens', golden elm, grows to about 15 m (50 ft). It is an attractive tree, providing good foliage contrast with other green trees. 'Pendula' grows to 20 m (65 ft), with long, leafy branches drooping to the ground.

U. minor (Synonym: U. carpinifolia), smooth-leafed elm, zone 5, is native to Europe, western Asia and North Africa. Growing to around 30 m (100 ft) in its habitat, it is unlikely to exceed 15-20 m (50-65 ft) in cultivation. The glossy, oval leaves are 5-10 cm (2-4 in) long and the late winter flowers appear in thick clusters before the leaves appear. Cultivar 'Variegata' has pretty foliage, irregularly splashed and spotted in creamy white.

U. parvifolia, Chinese elm, zone 5, is a shapely tree, 12-20 m (40-50 ft) tall, with spreading branches and an attractively mottled trunk, in shades of dark gray, red-brown and cream. The dark green foliage is evergreen in all but very cold regions. It is a native of China and Japan.

U. procera, English elm, zone 6, is a magnifiÂcent tree which can grow to heights of 45 m (145 ft), but more often 20-30 m (65-100 ft). Unfortunately, it is one of the species that has succumbed to Dutch elm disease in the north-ern hemisphere. It has a rounded crown and smallish, rounded leaves. It suckers badly unless grafted onto U. glabra stock. Cultivar 'Argenteovariegata' has leaves spotted or striped with yellow and white; 'Louis van Houtte', with leaves coloured butter yellow, is not often available.

U. pumila, Siberian elm, zone 3, from eastern Siberia and northern China, is a hardy species with rapid growth. With broad, erect habit and sometimes shrubby, it grows to 4-12 m (13-40 ft). The dense foliage is deep golden yellow in autumn. It appears resistant to Dutch elm disease, and is being used to breed new hybrid cultivars.

Cultivation

Elms do well in cool, moist cliÂmates. They prefer deep soils that are well drained but retain moisture, and require ample water through the growing season. Propagation is from seed sown outdoors in autumn, and from semi-ripe cuttings in summer, rooted with bottom heat. Cultivars are usually budded or grafted. Dutch elm disease, which is transmitÂted by the elm bark beetle, has now almost wiped out many elm species in North America and Europe. The American elm, UImus ameriÂcana, and the English elm, U. procera, are very susceptible and should not be planted. The disÂease is caused by a fungus and is transmitted by elm bark beetles which breed in the hark of dying elms and carry the spores to new growth of healthy trees, where the adult beetles feed on the soft young bark. The fungus enters and blocks the tree's sap, causing branches to die from lack of water. Progress of the disease is very rapid, with large trees dying mostly within one or two months. 'l'here is ongoing research to develop species or hybrids with resistance to the disease.