Mountain Ash Sorbus alnifolia

Sorbus alnifolia, or Mountain Ash, is a moderate to fast growing flowering tree that begins as pyramid-shaped but matures to a more rounded appearance. It grows best in moist, acidic, well-drained soils in full sun. A native of Asia, this tree prefers cool climates and will not grow well in the hot and humid summer conditions south of USDA Zone 7. It generally requires little pruning, but if you are driven to prune, apply your skills from late fall to early spring. It is less susceptible to pest and disease than other Sorbus spp., but is not a good street tree and is not tolerant of air pollution. The plant tolerates strong winds but not maritime exposure It is, however, easy to transplant.

Mountain Ash, is noted for its attractive form, creamy white flowers, simple beach-like leaves, red fall fruit and good fall color. Golden orange fall color can be outstanding.

Insects, Diseases, and Other Plant Problems:

Mountain Ash is noted for its resistance to borers that attack other species of mountain ash. It is considered to be one of the best of the mountain ashes because of its pest resistance and form. However, bacterial fireblight can be a severe problem, causing scorched leaves at the branch ends. Scab can cause significant defoliation. Cankers, crown gall, powdery mildew and rust may also occur. Insect visitors include aphids, sawfly and scale. Stressed trees are generally more susceptible to attack from canker and borers.