Tree of Merit: Korean mountainash
(Sorbus alnifolia)
by Michelle Sutton, City Trees Editor
Potential Height: 20 to 40 ft (6 to 12 m)
Potential Width: 15 to 25 ft (4.6 to 7.6 m)
I can think of few trees with the year-round beauty
of Korean mountainash (Sorbus alnifolia). It is notable for its
delicate and showy white spring flowers, handsome deeply
veined summer foliage, yellow to orange fall color, red-
dish-pink berries in fall and early winter, and elephantine bark
in winter (beech-like, but with distinct white markings). The
cultivar 'Redbird' has rosy-red fruits and a more upright form.
Despite its common name, Korean mountainash is a member
of the Rose family, and like so many other members of that
family tends to bear its flowers and fruit more heavily in alter-
nate years. Birds are attracted to the fruits, which are pomes,
botanically speaking. The tree is native to Japan and China as
well as Korea. It prefers full sun but can tolerate part shade.
Korean mountainash has stronger wood and more borer
resistance than its European mountain ash counterparts. To
reduce the chance for fireblight infection, it should be pruned
in the winter. Its early structural pruning should take into
account the tree's tendency toward narrow crotch angles.
The Cornell Urban Horticulture Institute (UHI) reports that
in Ithaca, NY, Korean mountainash is successfully trans-
planted bare root at two-inch caliper or less, spring or
fall. UHI has had success growing it in CU-Structural Soil
installations. It is recommended as a specimen tree for
parks, large parking lot islands, and generous tree lawns
where it can get its water needs met, as it doesn't tol-
erate prolonged periods of drought. It can thrive in a
wide range of soil pH (5.0 to 8.0). Korean mountainash
performs best in USDA Hardiness Zones 4b to 7. As an
underutilized tree, this beauty carries extra charm.
urban-forestry.com 39
Delicate Korean mountainash flowers, five-
petaled as per the Rose family. Photo Courtesy
Missouri Botanical Garden Plant Finder
Vertically striated trunk of mature Korean
mountainash. Photo by Michelle Sutton
Fruit and sporadic fall leaf color.
Photo by Michelle Sutton
Michelle Sutton has been City Trees Editor since
2005. She is also Editor for the New York State Urban
Forestry Council. Michelle has a master's degree
in Urban Horticulture from Cornell University.
