Chinese Elm, Chinese Evergreen Elm
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 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.
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