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Ulmus

Elm
Ulmaceae
Deciduous, Trees

Once highly prized shade trees, elms have fallen on hard times. Dutch elm disease (spread by a bark beetle) has killed millions of American elms in North America and can attack most other elm species. Many of the larger elms are appealing fare for various types of aphids, beetles, leafhoppers, and scale, making them time-consuming to care for, messy, or both. Elms have other problems not related to pests. They have aggressive, shallow root systems, so you’ll have trouble growing other plants beneath them. Many produce suckers; branch crotches are often narrow, splitting easily in storms. Still, elms are widely planted, and researchers continue to devote much effort to finding disease-resistant varieties. Elms tolerate a wide range of soils. Poor yellow fall color except as noted.

Ulmus americana

Native to eastern North America. This majestic, arching deciduous tree once graced lawns and streets throughout its range, but it has been decimated by Dutch elm disease. Fast growth to 100 ft. or taller with nearly equal—sometimes greater—spread. Main branches are upright, outer ones pendulous. Rough-surfaced, 3–6-in.-long, toothed dark green leaves; great variation in shade of yellow fall color. Leafs out very late where winters are mild. Pale green, papery seeds make a mess in spring. Disease-resistant varieties include ‘Princeton’ (upright, to 65 ft. tall), ‘Valley Forge’ (vase-shaped, to 70 ft. tall), and ‘Jefferson’ (vase-shaped, to 70 ft. tall).

Ulmus hybrids

Many institutions have been carrying on breeding experiments involving various elms to produce trees resistant to Dutch elm disease. Among them, ‘Accolade’ has the best track record so far; it grows to 70 ft. tall and 60 ft. wide, with arching limbs and a vase shape much like that of American elm. ‘Danada Charm’ has a similar size and shape but is ganglier in youth. ‘Frontier’, just 40 ft. tall and 30 ft. wide, features reddish purple leaves in fall. ‘Homestead’, to 55 ft. tall and 35 ft. wide, has a symmetrical oval to pyramidal form. ‘Patriot’ forms a narrow vase shape to 50 ft. tall and half as wide. ‘Triumph’ grows to 55 ft. tall and 50 ft. wide; it forms an upright oval with a strong central leader.

Ulmus parvifolia
Ulmus parvifolia

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Ulmus parvifolia

Semievergreen or deciduous, according to winter temperatures and the individual tree’s heredity. From China, Korea, and Japan. Fast growth to 40–60 ft. tall and 50–70 ft. wide; often reaches 30 ft. in 5 years. Form is extremely variable, but trees are generally spreading, with long, arching, eventually weeping branchlets. On older trees, the bark of the trunk sheds in patches (somewhat like the bark of sycamore, Platanus), often creating beautiful mottling. Leathery dark green, 3/4–2 1/2-in.-long, evenly toothed leaves. Round fruit is produced in fall. Patio tree, sun screen, or (with careful pruning) street tree. Rub or cut out small branches along the trunk for the first few years; shorten overlong branches or strongly weeping ones to strengthen scaffolding. Older trees may need thinning to lessen chance of storm damage. Subject to Texas root rot in desert but otherwise little bothered by pests or diseases.

Forms that hold their leaves are often sold as ‘Sempervirens’, but that is not a true variety. Two commonly offered, more or less evergreen varieties are ‘Brea’, with larger leaves and more upright habit than the species; and ‘Drake’, with smaller leaves, weeping habit. A more reliably evergreen variety is round-headed ‘True Green’, with small, deep green leaves. Other selections include ‘Allee’ (‘Emer II’), vase-shaped tree to 70 ft. tall and 60 ft. wide; ‘Athena Classic’ (‘Emer I’), moderately fast grower to 35 ft. tall and 50 ft. wide; and ‘Dynasty’, to 40 ft. by 40 ft., vaselike when young, later rounded. ‘Everclear’ has a narrow habit to 40 ft. tall and 15 ft. wide. There are also dwarf varieties commonly used for bonsai.

A note of caution: A less desirable species, U. pumila (Siberian elm), is sometimes sold as Chinese elm.

Ulmus pumila

Deciduous, native to Russia and northern China. Grows to 50 ft. tall and 40 ft. wide. Smooth dark green leaves are 3/4–2 in. long. Resists Dutch elm disease and endures cold, heat, aridity, and poor soil—but has brittle wood and weak crotches and is not a desirable tree. Possibly useful in holding soil against erosion; fast growth also makes it suitable for a windbreak or shelter belt. Papery, winged seeds disperse seedlings over a wide area.

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