Mountain ash, also called rowan, is a small to medium ornamental tree prized for its fern-like leaves, flat clusters of white spring flowers and heavy crops of orange-red berries that birds strip from the branches in fall and winter. It grows best in the cool northern tier of the US, roughly USDA zones 2 to 6 depending on species, in full sun to light shade and moist, well-drained, slightly acidic soil. It dislikes hot summers, drought, compacted ground and road salt. Plant it in fall or spring, water it well for the first two years, prune only in late winter, and watch for fire blight, borers and winter sunscald, the three problems that shorten its life most often.
In this guide
Key Takeaways
- Best in cool climates, about zones 2 to 6; it struggles in hot, humid summers.
- Full sun to part shade in moist, well-drained, slightly acidic soil.
- Grows about 20 to 40 feet tall, often with a rounded to oval crown.
- Berries ripen late summer to fall and feed waxwings, robins, thrushes and grosbeaks.
- Not a true ash, so emerald ash borer does not attack it, but fire blight, borers and sunscald do.
Mountain Ash Species and Varieties
Mountain ashes belong to the genus Sorbus in the rose family. They are not related to true ashes (Fraxinus); the name comes from their similar compound leaves. That distinction matters because emerald ash borer, which has killed millions of true ash trees, does not attack mountain ash.
| Species | Typical zones | Typical size | Notes |
|---|---|---|---|
| European mountain ash, rowan (Sorbus aucuparia) | 3 to 6 (to 7 in cool areas) | 20 to 40 ft tall, 15 to 25 ft wide | Most widely planted; many cultivars |
| American mountain ash (Sorbus americana) | 2 to 6 | 15 to 30 ft tall | Native to the Northeast, Great Lakes and Appalachians; often multi-stemmed |
| Showy mountain ash (Sorbus decora) | 2 to 6 | 15 to 30 ft tall | Native to the northern US and Canada; large, showy fruit clusters |
| Korean mountain ash (Sorbus alnifolia) | 4 to 7 | 30 to 40 ft tall | Simple, not compound, leaves; often more heat tolerant |
Popular European rowan cultivars include ‘Cardinal Royal’, selected for an upright habit and bright red fruit, and ‘Black Hawk’, a columnar selection with thick, dark leaves. If you want a native tree for wildlife, choose American or showy mountain ash from a local nursery.
Where Mountain Ash Grows Best
Rowans are trees of cool, moist mountain slopes and northern forests. In the US they thrive in New England, the upper Midwest, the northern Rockies and the Pacific Northwest. South of about zone 6, or anywhere with long hot, humid summers, they tend to be short-lived and stressed, which invites borers and disease.
- Light: full sun gives the best flowering and fruiting; light afternoon shade helps in warmer spots.
- Soil: moist, well-drained, slightly acidic (pH roughly 5.5 to 6.5) loam is ideal. It tolerates sandy soils if watered but struggles in heavy, compacted clay and alkaline soils.
- Avoid: reflected heat from pavement and south-facing walls, road salt spray, and very dry or exposed windy sites in the warmer end of its range.
- Spacing: plant at least 15 to 20 feet from buildings and other trees for a single specimen; columnar types need less room.
How to Plant a Mountain Ash
Plant in early fall, about six weeks before the ground freezes, or in spring once the soil can be worked. Fall planting gives roots time to grow before summer heat.
- Find the root flare. Remove excess soil from the top of the root ball until you see where the trunk widens into roots.
- Dig wide, not deep. Make the hole two to three times as wide as the root ball and only as deep as the distance from the root flare to the bottom of the root ball.
- Loosen or tease circling roots on container trees; cut away twine and as much burlap and wire basket as you can on balled trees once they are in the hole.
- Set the tree so the root flare sits at or slightly above grade. Planting too deep is a common cause of slow decline.
- Backfill with the native soil, breaking up clods and firming gently to remove air pockets. Heavy amendment of the hole is not necessary.
- Water deeply to settle the soil, then build a low soil ring around the root ball to hold water.
- Mulch 2 to 4 inches deep in a wide circle, keeping mulch a few inches away from the trunk.
- Stake only if needed in windy sites, with loose ties, and remove stakes after one growing season.
Growing from seed
Mountain ash is easy but slow to grow from seed, and seedlings of cultivars will not match the parent. Collect ripe berries in fall, mash them in water and rinse away the pulp, which contains germination inhibitors. The seeds need several months of cold, moist conditions before they sprout, so either sow them outdoors in a protected seedbed or pot in fall and let winter do the work, or mix them with damp sand in a bag and refrigerate them for about three to four months before sowing in spring. Seedlings typically take several years to reach a plantable size, so most homeowners buy nursery trees instead.
Caring for Mountain Ash
Watering
Mountain ash has relatively shallow roots and does not tolerate drought well. For the first two years, give about 1 inch of water per week, including rain, soaking the root zone slowly rather than sprinkling lightly. Established trees still benefit from deep watering every week or two during dry spells. Drought stress is the main reason borers and cankers move in, so this is the single most important care step.
Mulching
A wide ring of shredded bark or wood chip mulch keeps roots cool and moist, reduces competition from turf, and keeps mowers and string trimmers away from the trunk. Wounds from mowers are a common entry point for borers and disease.
Fertilizing
Most mountain ashes need little fertilizer. Avoid heavy nitrogen, which pushes soft, succulent growth that is more vulnerable to fire blight. If a soil test shows deficiencies or the tree is pale and slow, a light application of a balanced slow-release fertilizer in early spring is enough.
Pruning
Prune in late winter while the tree is dormant and before buds break. Remove dead, damaged and crossing branches, water sprouts and suckers from the base, and keep a single central leader on young trees if you want a classic tree form. Avoid pruning in spring and early summer when fire blight bacteria spread readily in warm, wet weather. Our guide on when to prune trees and shrubs covers timing for other trees in your yard.
Winter protection
Mountain ash has thin bark that is prone to sunscald and frost cracks, especially on the south and southwest side of young trees. Winter sun warms the bark, then nightfall freezes it, killing the tissue beneath. Wrap the trunks of young trees with a light-colored tree wrap or guard from late fall to early spring, and remove it in spring. Planting where a building or other trees shade the trunk in winter also helps.
Berries for Birds
The berries, technically small pomes, ripen from late summer into fall and often hang on into winter until birds find them. Cedar waxwings, American robins, thrushes, grosbeaks and, in northern areas, Bohemian waxwings and pine grosbeaks feed on them heavily. A fruiting rowan can bring flocks of waxwings into a yard in a single afternoon.
To maximize wildlife value, plant mountain ash alongside other fruiting natives that ripen at different times, such as serviceberry and winterberry. Our guides to growing a serviceberry tree and attracting birds to your garden have more ideas.
Rowan berries are traditionally cooked into jellies and preserves in Europe. Raw berries are very bitter and contain parasorbic acid, which can upset the stomach, so do not eat them raw. Cooking converts it to a harmless compound. Keep children from snacking on them.
Pests and Diseases
Fire blight
A bacterial disease of the rose family that also attacks apples, pears and crabapples. Infected shoot tips wilt, blacken and curl into a shepherd’s crook, and leaves look scorched but stay attached. Prune out infected branches in dry weather during dormancy, cutting 8 to 12 inches below visible damage, and disinfect pruners between cuts. Avoid excess nitrogen and overhead irrigation.
Borers
Roundheaded appletree borer and other wood-boring beetles tunnel into stressed trees near the base of the trunk, leaving round holes and sawdust-like frass. The best defense is a healthy, well-watered tree with no mower wounds. Severely infested trees often decline and may need removal; a certified arborist can advise on treatment options.
Mountain ash sawfly
Caterpillar-like larvae feed in groups and can strip leaves from branches in early summer. Small infestations can be pruned off or knocked into soapy water; heavy repeated defoliation may need treatment. Insecticidal products that target caterpillars, such as Bt, do not work on sawflies, which are not caterpillars.
Other issues
- Cankers: sunken, discolored bark areas from fungal infection, usually on stressed trees. Prune out affected branches.
- Scale insects and aphids: sticky honeydew and sooty mold; dormant oil in late winter helps control scale.
- Leaf scorch: brown leaf edges in hot, dry weather, a sign the site is too hot or dry.
- Short lifespan in warm zones: often 15 to 20 years where summers are hot, longer in cool climates.
Seasonal Care Calendar
| Season | Tasks |
|---|---|
| Late winter | Prune while dormant; check for cankers and borer holes; apply dormant oil if scale is present |
| Spring | Remove trunk wrap; refresh mulch; watch for fire blight after bloom |
| Summer | Deep water during dry spells; check for sawfly larvae |
| Fall | Enjoy berries and birds; plant new trees; water before ground freezes |
| Early winter | Wrap young trunks against sunscald; keep mulch away from trunk to deter rodents |
For more small ornamental trees suited to northern yards, browse our trees and shrubs guide.
Frequently Asked Questions
Is mountain ash the same as a rowan tree?
Yes. Rowan is the common name for European mountain ash, Sorbus aucuparia. North American species such as Sorbus americana are also called mountain ash.
How fast does a mountain ash grow?
It grows at a moderate rate, often around 1 to 2 feet per year when young in good conditions, slowing as it matures.
Does emerald ash borer affect mountain ash?
No. Mountain ash is in the rose family, not a true ash, so emerald ash borer does not attack it.
Are mountain ash berries poisonous?
Raw berries are bitter and can cause stomach upset. They are traditionally cooked into jelly, which breaks down the irritating compound. Birds eat them safely.
Can I grow mountain ash in a warm climate?
It is best in zones 2 to 6. In hotter areas it tends to be stressed and short-lived; Korean mountain ash or serviceberry are better choices there.