Tree · Rosaceae
Western mountain ash
Sorbus sitchensis · includes its varieties and subspecies
Western mountain ash is recorded as native to 6 states and territories in Kew’s World Checklist of Vascular Plants and USDA PLANTS, and recorded in 61 counties of those states by USDA PLANTS.
Key facts · USDA PLANTS
Western mountain ash at a glance
- Native in
- 61 counties, across 6 states and territories
- Estimated cold hardiness
- Zone 4b PLANTS minimum temperature −28°F
- Mature height
- 15 ft PLANTS mature height
- Light and water
- Full sun (shade-intolerant) Medium water use
Estimated cold hardiness: zone 4b. PLANTS gives a minimum temperature of −28°F; zone 4b winters bottom out at −25°F, the coldest half-zone that stays within that limit.
Western mountain ash is recorded as native to 6 states and territories in Kew’s World Checklist of Vascular Plants and USDA PLANTS, and recorded in 61 counties of those states by USDA PLANTS.
Counties where it is native
The 15 counties with the most ZIP codes among the 61 where it is listed.
Native counties by state
- Alaska 8 counties
- California 1 county
- Idaho 6 counties
- Montana 1 county
- Oregon 25 counties
- Washington 20 counties
Growing traits
Values from the PLANTS characteristics record of a variety (SOSIG). “Not recorded” means PLANTS has no value; nothing here is estimated except the zone.
Growth
- Growth habit
- Shrub, Tree
- Duration
- Perennial
- Mature height
- 15 ft
- Growth rate
- Slow
- Growth form
- Single Stem
- Shape
- Erect
- Lifespan
- Moderate
- Active growth period
- Spring and Summer
Light and water
- Shade tolerance
- Intolerant (full sun (shade-intolerant))
- Moisture use
- Medium water use
- Drought tolerance
- Low
- Tolerance of waterlogged soil
- None
- Precipitation range
- 20 to 40 in per year
Soil
- Soil textures
- Coarse, medium and fine
- pH range
- 6 to 7.2
- Lime (CaCO₃) tolerance
- None
- Salinity tolerance
- None
- Fertility requirement
- Medium
- Minimum root depth
- 16 in
Climate
- Minimum temperature
- −28°F
- Estimated cold hardiness
- Zone 4b and warmer
- Minimum frost-free days
- 100
- Fire tolerance
- Low
Flowers, leaves and fruit
- Flower color
- White
- Showy flowers
- Yes
- Bloom period
- Late Spring
- Foliage color
- Dark Green
- Showy in fall
- Yes
- Keeps leaves
- No
- Fruit color
- Red
Other
- Toxicity
- None
- Nitrogen fixation
- None
- Nursery availability
- Contracting Only
- Family
- Rosaceae
- PLANTS symbol
- SOSI2
Source & data date
- Source
- USDA NRCS PLANTS Database: county distribution records, native status and plant characteristics. CC0 (public domain dedication, per the data.gov catalog record).
- Kew’s World Checklist of Vascular Plants (WCVP): native or introduced status by state. CC BY 3.0.
- USGS US-RIIS (ver. 2.0): species listed as introduced are excluded. CC0.
- Citation
- USDA, NRCS. 2026. The PLANTS Database (https://plants.usda.gov, 11/04/2026). National Plant Data Team, Greensboro, NC USA.
- Govaerts R. (ed.) (2026). WCVP: World Checklist of Vascular Plants. Facilitated by the Royal Botanic Gardens, Kew. Data file dated 2026-06-04, http://sftp.kew.org/pub/data-repositories/WCVP/ (retrieved 2026-11-04). Paper: Govaerts R. et al. (2021) The World Checklist of Vascular Plants, a continuously updated resource for exploring global plant diversity. Scientific Data 8, 215.
- Data date
- Retrieved from PLANTS on November 4, 2026; WCVP data file dated June 4, 2026.
- Scope
- Sorbus sitchensis (PLANTS symbol SOSI2), including 1 variety or subspecies folded into the species.
- Method
- A species is listed when it is recorded as native to the state in Kew’s World Checklist of Vascular Plants and USDA PLANTS, and recorded in the county by USDA PLANTS. Species PLANTS labels both native and introduced are listed separately. Full method · All sources