Sorbus americana, or American mountain ash, is a small, deciduous, understory tree that is native to northeastern North America from Newfoundland to Manitoba south to northern Illinois, northern Michigan and New Jersey plus further south in the Appalachians to Georgia. It typically grows to 15-30’ tall with an open rounded crown. It is noted for its attractive form, white spring flowers, serrate compound-pinnate leaves and bright orange-red fall fruit. Smooth, gray bark becomes scaly with age. Dense flattened clusters (corymbs to 3-6” across) of very small 5-petaled white flowers (each to 1/4” wide) appear in May. Flowers are followed by bright red berries (each to 5/16” diameter) that ripen in late summer and remain on the tree after leaf-drop. Berries are attractive to birds and animals, but too acidic to be eaten fresh off the tree by humans. Berries may be made into jellies. Each pinnate leaf (6-10” long) typically has 9-17 sharply serrated, lance shaped, dark green leaflets (2-4” long) with gray-green undersides. Foliage turns yellow in fall. Mountain ashes usually have ash-like leaves, but are members of the rose family, and are not related to true ashes (Fraxinus), which are in the olive family.
They are best grown in moist, acidic, humusy, well-drained soils in full sun, or part shade where it is hotter. As the common name suggests, this is a tree of cool mountain climates that dislikes dry soils and hot/humid summers of the deep south. EWe grow it nicley in USDA Zone 6. It is somewhat intolerant of urban pollution. It generally requires little pruning. Prune if needed from late fall to early spring.
Stressed trees are generally more susceptible to attack from various insects and fungi. We do not recommend fertilizing, as fireblight might be a problem if overdone.
It makes a nice lawn specimen or small shade tree for cooler climates, or use the microclimate of your yard by shading it from the hotter midday sun.
Modified and Adapted from Missouri Botanic Garden Plant Finder