North America Native Plant

Western Mountain Ash

Botanical name: Sorbus sitchensis

USDA symbol: SOSI2

Life cycle: perennial

Habit: shrub

Native status: Native to Alaska âš˜ Native to Canada âš˜ Native to the lower 48 states  

Western Mountain Ash: A Native Gem for Cool Climate Gardens If you’re looking for a native plant that combines year-round beauty with exceptional wildlife value, let me introduce you to the western mountain ash (Sorbus sitchensis). This charming shrub is like the Swiss Army knife of native plants – it’s ...

Western Mountain Ash: A Native Gem for Cool Climate Gardens

If you’re looking for a native plant that combines year-round beauty with exceptional wildlife value, let me introduce you to the western mountain ash (Sorbus sitchensis). This charming shrub is like the Swiss Army knife of native plants – it’s attractive, functional, and perfectly adapted to life in cooler climates across western North America.

What is Western Mountain Ash?

Western mountain ash is a perennial, multi-stemmed woody shrub that typically grows 4-16 feet tall. Don’t let the name fool you – it’s not actually related to true ash trees! This native beauty belongs to the rose family and has earned its place in gardens through sheer versatility and charm.

As a true native, western mountain ash calls Alaska, Canada, and the western United States home. You’ll find it naturally growing across an impressive range that includes Alberta, British Columbia, Alaska, California, Yukon, Idaho, Montana, Oregon, and Washington.

Why Plant Western Mountain Ash?

There are plenty of reasons to fall in love with this native shrub:

  • Four-season interest: Attractive compound leaves provide texture, white flower clusters brighten spring, brilliant red-orange berries add fall drama, and interesting branching structure shines in winter
  • Wildlife magnet: Those gorgeous berries aren’t just for show – they provide 5-10% of the diet for many terrestrial birds
  • Pollinator friendly: Spring flowers attract bees and other beneficial insects to your garden
  • Adaptable nature: With a facultative wetland status in most regions, it can handle both moist and drier conditions
  • Cold hardy: Thrives in USDA zones 2-7, making it perfect for challenging climates

Perfect Garden Roles

Western mountain ash shines in several landscape scenarios:

  • Native plant gardens: As a true native, it fits perfectly into indigenous plant collections
  • Wildlife gardens: The bird-attracting berries make it a must-have for backyard wildlife enthusiasts
  • Naturalistic landscapes: Its informal growth habit works beautifully in less formal garden settings
  • Mountain or alpine gardens: Naturally adapted to higher elevations and cooler conditions
  • Specimen planting: Attractive enough to stand alone as a focal point

Growing Conditions and Care

The good news? Western mountain ash is relatively low-maintenance once established. Here’s what it needs to thrive:

  • Light: Partial shade to full sun, though it appreciates some protection in hotter climates
  • Soil: Well-draining soil with consistent moisture; adaptable to various soil types
  • Water: Regular watering during establishment, then moderate moisture (it can handle both wet and dry periods thanks to its facultative status)
  • Climate: Prefers cooler conditions; thrives in zones 2-7

Planting and Care Tips

Getting your western mountain ash off to a great start is straightforward:

  • Timing: Plant in spring or fall for best establishment
  • Spacing: Allow room for mature size – these shrubs can spread as wide as they are tall
  • Watering: Keep soil consistently moist during the first growing season
  • Mulching: Apply 2-3 inches of organic mulch around the base to retain moisture and suppress weeds
  • Pruning: Minimal pruning needed – just remove dead or damaged branches in late winter

The Bottom Line

Western mountain ash is one of those rare plants that truly earns its keep in the garden. It’s beautiful, supports local wildlife, adapts to various conditions, and requires minimal fuss once established. For gardeners in cooler climates looking to create habitat while adding year-round interest, this native shrub deserves serious consideration.

Whether you’re creating a wildlife sanctuary, building a native plant collection, or simply want a reliable shrub that looks good and does good, western mountain ash delivers on all fronts. Your local birds will thank you, and your garden will be more beautiful for it!

Wildlife Status

Want to attract wildlife or keep hungry critters away from your garden? Understanding the relationship between plants and wildlife is key. While plant tags may indicate deer and rabbit resistance, they don't tell the full story. Every gardener has experienced the disappointment of purchasing "deer-resistant" plants only to find them nibbled to the ground!

The extent to which plants are resistant to animal browsing is a matter of degree. Likewise, the extent to which a plant attracts wanted visitors also varies. Whether you want a garden full or free of wildlife, learning about interactions between a plant and wild animals can help you make smarter choices for the garden you desire.

As shown below Shrubby Indian Mallow isn't a large food source for animals or birds. You can confidently add this plant to your garden and rest assured knowing it's unlikely to be devoured by four-legged visitors.

Small animals

not a food source

not a source of cover

Large animals

not a food source

not a source of cover

Terrestrial birds

5-10% of diet

Infrequently used as cover

Water birds

not a food source

not a source of cover

Sources:

Quinlan, S.E., and S. Cuccarese. 2004. Native Alaskan and exotic plants used by wildlife. Alaska Department of Fish and Game. Anchorage.

Western Mountain Ash

Classification

Group

Dicot

Kingdom

Plantae - Plants

Subkingdom

Tracheobionta - Vascular plants

Superdivision

Spermatophyta - Seed plants

Division

Magnoliophyta - Flowering plants

Subdivision
Class

Magnoliopsida - Dicotyledons

Subclass

Rosidae

Order

Rosales

Family

Rosaceae Juss. - Rose family

Genus

Sorbus L. - mountain ash

Species

Sorbus sitchensis M. Roem. - western mountain ash

Plant data source: USDA, NRCS 2025. The PLANTS Database. https://plants.usda.gov,. 2/25/2025. National Plant Data Team, Greensboro, NC USA