Though vulnerable to pests and diseases in some areas, mountain ashes are still popular ornamental or shade trees because of their size (most are under 50 feet), their repaid growth their flat clusters of white flowers in spring and in particular their showy, long-lasting red-orange berries, which the birds like as much as we do. Mountain ash even has showy red orange foliage in fall. In short, it is worth trying, though perhaps not a safe bet for mass plantings. There’re a number of garden worthy mountain ashes, some of them native to the U.S European mountain ash, or rowan tree (Sorbus aucuparia), is the most widely grown. However, it is hardy to zone 3 and grows as tall as 45 feet, with rather fernlike leaves “Fastigiata” is an upright variety, and “Xanthocarpa” has yellow berries, Korean mountain ash (S. Alnifolia), hardy to at least Zone 5, can sometimes grow as tall as 60 feet and has a round ed head that can extend all the way to the ground, though you might want to remove lower branches so as to view the smooth, gray bark of the trunk. Both the berries and the autumn leaves are extremely showy, though the foliage is not as finely cut as that of European mountain ash.
How to Grow Mountain Ash
You can plant the trees balled and-burlapped in full sun and a moist but well drained soil. Newly planted trees benefit from staking. Fire blight may blacken the ends of branches, especially in the south. Affected branches should be pruned out. Young trunks may need to be protected from sun scald in the north. Borers may be found in the trunk near the ground in some regions in the east and can be destroyed by probing their burrows with a wire laborious, but a labor of love if you have a fine tree. (Korean Mountain ash is somewhat resistant to borers). Older trees rarely need pruning, but young ones can be pruned in winter or early spring to produce one central leader and to remove crossed or vertical branches or ones with weak crotches. You may prune multi trunked trees to a single trunk while they’re young, if desired and remove lower branches to allow headroom.