ENH-756

Sorbus alnifolia: Korean Mountain Ash1 Edward F. Gilman and Dennis G. Watson2

Introduction Uses: tree lawn 3-4 feet wide; tree lawn 4-6 feet wide; tree lawn > 6 ft wide; reclamation; specimen; street without Korean mountain ash grows rather quickly into a 20- to sidewalk; parking lot island 100-200 sq ft; parking lot island 40-foot-tall deciduous tree with a broad, rounded, 15- to > 200 sq ft 25-foot-wide, dense canopy which casts dense shade below. Availability: somewhat available, may have to go out of the Young trees form a dense oval. The two to four-inch-long, region to find the tree glossy, bright green, simple leaves change to attractive hues of yellow, orange, and rust in fall before dropping. In late spring the trees are decorated with two to three-inch- diameter, flat-topped clusters of tiny white blossoms, which may appear in great number one year yet sparsely the next. These blooms are followed by the production of small but very showy, red to yellow fruits which pendulously hang in five-inch clusters of two to ten berries from tree branches. Fruit clusters are not as dense as those of Sorbus aucuparia. The smooth, grey bark of the branches provides a nice contrast for these colorful fruits. These attractive, abundant fruits ripen and cling to the tree, providing a welcome feast for various types of weary, migrating birds. Fruit are displayed nicely after leaves fall in autumn. General Information Scientific name:Sorbus alnifolia Figure 1. Mature Sorbus alnifolia: Korean mountain ash Pronunciation: SOR-bus al-nih-FOLE-ee-uh Common name(s): Korean mountain ash Description Family: Rosaceae Height: 20 to 40 feet USDA hardiness zones: 4A through 7A (Fig. 2) Spread: 15 to 25 feet Origin: not native to North America Crown uniformity: symmetrical Invasive potential: little invasive potential Crown shape: oval, vase Crown density: dense

1. This document is ENH-756, one of a series of the Environmental Horticulture Department, UF/IFAS Extension. Original publication date November 1993. Revised December 2006. Reviewed February 2014. Visit the EDIS website at http://edis.ifas.ufl.edu.

2. Edward F. Gilman, professor, Environmental Horticulture Department; and Dennis G. Watson, former associate professor, Agricultural Engineering Department, UF/IFAS Extension, Gainesville, FL 32611.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county’s UF/IFAS Extension office. U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension. Growth rate: fast Trunk and Branches Texture: medium Trunk/bark/branches: branches don’t droop; not showy; typically multi-trunked; thorns Foliage Pruning requirement: little required Leaf arrangement: alternate (Fig. 3) Breakage: susceptible to breakage Leaf type: simple Current year twig color: brown Leaf margin: serrate, double serrate Current year twig thickness: medium Leaf shape: elliptic (oval), ovate Wood specific gravity:unknown Leaf venation: pinnate Leaf type and persistence: deciduous Culture Leaf blade length: 2 to 4 inches Light requirement: full sun Leaf color: green Soil tolerances: clay; sand; loam; slightly alkaline; acidic; Fall color: yellow, red, copper, orange well-drained Fall characteristic: showy Drought tolerance: moderate Aerosol salt tolerance: moderate

Other Roots: not a problem Winter interest: no Outstanding tree: yes Ozone sensitivity: unknown Verticillium wilt susceptibility: unknown Pest resistance: resistant to pests/diseases Use and Management Figure 2. Range Partially due to the upright habit, weak crotches can develop on branches which are allowed to grow to larger than about half the diameter of the trunk. Pruning early in the life of the tree will improve the structure of the tree and help increase longevity in the landscape.

It is tempting to plant this tree due to the nice flowers, nice fruit display and bright fall color, but it may be short-lived and is susceptible to fireblight. But it is the most resistant of the mountain ashes to borers. It is probably best to locate the tree where there is adequate open soil space for root Figure 3. Foliage development so the tree will not be subjected to much stress. Provided with some irrigation in a dry summer, this Flower tree will serve the landscape well for a number of years. It Flower color: white/cream/gray has many outstanding attributes which people will enjoy for Flower characteristics: showy a number of years after planting. Plant it as an occasional specimen in a park or large landscape for ornamental value Fruit and diversity, not as a staple in large numbers. Fruit shape: round Fruit length: less than .5 inch, .5 to 1 inch Korean mountain ash should be grown in full sun on any Fruit covering: fleshy well-drained soil, including slightly alkaline. Any required Fruit color: red pruning should be done in winter or early spring to avoid Fruit characteristics: attracts birds; showy; fruit/leaves not exposing the wood to the fireblight disease. Fireblight can a litter problem cause serious damage to the tree.

Sorbus alnifolia: Korean Mountain Ash 2 The cultivar ‘Redbird’ has rosy red fruits which are quite popular with birds, and has a more upright form. There are other hybrids and cultivars, all with the same limitations.

Propagation is by seed, with difficulty, or by grafting.

Pests Aphids, pear leaf blister mite, Japanese leafhopper, mountain ash sawfly, and scales may infest this tree. Korean mountain ash is somewhat resistant to borers which affect other Sorbus species, and probably should be planted instead of European mountain ash.

Diseases Fireblight, crown gall, canker, leaf rusts, and scab may infect this tree.

Sorbus alnifolia: Korean Mountain Ash 3