If you live in the Northeast or the Midwest, you’ve probably heard of the emerald ash borer invasion, and you’re wondering why on earth anyone would plant an ash tree. Enter the Sorbus genus, which includes several trees we call “ash”—the Korean, American, and European mountain ashes—that are not ashes at all. The Korean mountain ash (Sorbus alnifolia) is an especially beautiful tree in all four seasons. In the spring it’s covered with clusters of white flowers and in summer and fall with bright red or orange fruit. Fall leaf color is a stunning golden-orange. Winter exposes the quiet beauty of its gray, beechlike bark.
Common name: Korean mountain ash
Botanical name: Sorbus alnifolia
Plant type: Deciduous tree
Zones: 4 to 7
Height: 40 to 70 feet tall
• Sun: Full sun or light shade
• Soil: Acidic, well-drained
• Moisture: Average
• Mulch: Mulch to help keep soil moist.
• Pruning: Little pruning needed
• Fertilizer: None needed
• By seed or cuttings
Pests and diseases
• Scale insects, sawflies, aphids, and borers may attack the tree.
• Vulnerable to cankers, fireblight, powdery mildew, and scab.
• S. alnifolia makes a good shade tree or a specimen tree. It’s happiest in a cool climate and doesn’t do well under the stress of urban pollution.
• Birds love the berries.
• Though most mountain ash species have compound leaves—several leaflets on a stem—the Korean mountain ash has simple leaves that look like beech leaves.
All in the family
• Other trees in the Rosaceae family include hawthorns, juneberries, chokeberries, cherries, apples, peaches, and plums.
• There are about 100 species in the Sorbus genus. It’s one of the largest genera in the rose family.
• True ashes—those affected by the emerald ash borer—are in the Fraxinus genus, which is in the olive family (Oleaceae).
Where to buy
• Forestfarm, Williams, OR, 541-846-7269, www.forestfarm.com
(Photo of Sorbus alnifolia by Tracy Walsh.)