Showy Mountain Ash

Size, growth and what to expect

Showy mountain ash grows slowly, about a foot a year in our growth estimator. Expect a tree of 20 to 40 feet, sometimes with several stems, and a crown 15 to 20 feet wide that opens and rounds with age. Its wood is weak and brittle. It needs cool summers and does poorly where summers are hot and humid.

Flat clusters of white flowers, 3 to 6 inches across, open from May into July, about a week after American mountain ash. The scarlet berries, 3/8 to 1/2 inch across, ripen from August to November and can hang on into March. They weigh the branches down, and songbirds, waterfowl and small mammals eat them. The leaves turn yellow to red in fall.

It grows wild from Greenland and Labrador west to Manitoba, and south to Minnesota, northeast Iowa, northern Ohio, New York and New England. Look for it on rocky slopes and ledges, in cool, moist woods and along lake and stream shores. Where the two meet, it grows higher up than American mountain ash.

How to grow Showy Mountain Ash

Showy mountain ash wants full sun or light shade and a cool, moist, acid soil. It takes wet ground along a shore but not drought, salt or the polluted air of a city street. Keep it to cool northern yards and high ground. Plant it 15 feet from a wall and at least 15 feet from overhead wires, and set trees 15 feet apart.

Saplings ship bare-root or potted. Plant them dormant, from leaf fall until bud swell, in a hole wider than the roots and no deeper. Set the root flare at the soil line, put the native soil back in, and keep the mulch clear of the trunk. Sow seed in fall a quarter inch deep in a bed screened with hardware cloth, and let winter chill it. For spring, keep it damp in the refrigerator for 60 to 120 days first. Seed sown late or kept warm may wait a year or two to come up.

Water weekly through the first two summers and in dry spells after, since stressed trees invite borers and cankers. Guard the trunk from rabbits, voles and deer for the first few years. Prune only if needed, from late fall to early spring.

Each flower carries both male and female parts, so there are no male and female trees to pair. Fire blight is the worst trouble, scorching the leaves at the branch tips, and scab can strip a tree of its leaves. Cankers, crown gall, powdery mildew, rust, borers, aphids, sawflies and scale can also strike. Mountain ash is not a true ash, so emerald ash borer does not attack it. The raw berries are too bitter to eat, though they make jelly, and the seeds are toxic if eaten.