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Pictured: Sorbus sitchensis — the species. This variety isn’t separately illustrated.
Rosaceae family

Western Mountain Ash (var. grayi) Sorbus sitchensis var. grayi variety

Native
Deer-resistant — Low palatability to browsing deer. Usually passed over, but no plant is truly deer-proof when food is scarce.

Western Mountain Ash (var. grayi) is a perennial tree native to Alaska, Canada, and the lower 48 states. It grows to 15 ft and blooms May in part shade – shade, with red fruit.

Growing & care

USDA PLANTS · TRY
Conditions
Sources · Conditions
USDA PLANTS — Sun · Soil & moisture
USDA — SoilPH — Soil pH
USDA PLANTS (DwCA, Zenodo 17903503) — Fertility Requirement / Soil Adaptation — Fertility need · Adapts to
USDA — Temp-Min °F — Hardiness
Sun
Part shade – shade
Soil & moisture
Medium moisture
Soil pH
6–7.2
Fertility need
Medium
Adapts to
Coarse (sandy), Medium (loam), Fine (clay)
Hardiness
USDA zone 5+
Size & form
Sources · Size & form
USDA PLANTS (DwCA, Zenodo 17903503) — Height, Mature — Height
Derived (allometric) — width = height × functional-class crown ratio fit on USDA Urban Tree DB · Tallo; method per Jucker et al. 2022, Pretzsch et al. 2015 — Mature width
USDA PLANTS (DwCA, Zenodo 17903503) — Planting Density (per acre) — Spacing
USDA PLANTS (DwCA, Zenodo 17903503) — Growth Rate / Spread / Growth Form / Lifespan / Active Growth Period / Seed Period — Spread · Growth rate · Growth form · Active growth
USDA PLANTS — Lifespan
USDA PLANTS — FoliageTexture — Foliage
USDA PLANTS (DwCA, Zenodo 17903503) — Fruit/Seed Color / Fruit Persistence — Fruit
Lifespan: USDA’s lifespan scale for trees: short = under ~100 years · moderate = 100–250 · long = over 250. Balsam fir and other short-lived conifers are genuinely short for a tree, not short like an annual.
Height
15 ft
Mature width
~ 9 ft wide DERIVED derived estimate — open-grown crown allometry (height × growth-form ratio); not a measurement
Spacing
5–8 ft apart from USDA planting density
Spread
Moderate
Growth rate
Slow
Growth form
Single stem
Lifespan
Perennial · moderate
Foliage
fine texture
Active growth
Spring & summer
Fruit
Red persists into winter
In the garden
Sources · In the garden
USDA PLANTS (DwCA, Zenodo 17903503) — Propagation Method / Commercial Availability — Propagate by · In the trade
USDA PLANTS (DwCA, Zenodo 17903503) — Germination (cold stratification) — Seed starting
USDA PLANTS — Seed Period — Seeds ripen
USDA PLANTS (DwCA, Zenodo 17903503) — Foliage Texture / Browse Palatability / Resprout — Deer browsing · Resprouts if cut
Propagate by
Seed, Bare root, Container
Seed starting
Needs cold stratification a cold-moist spell before it germinates
Seeds ripen
Summer – Autumn seed-collection / harvest window
In the trade
Contract growing only
Deer browsing
Low often deer-resistant
Resprouts if cut
Yes regrows after top-kill
Shrub layer — Sits in the shrub of a layered food forest or polyculture.Open guide →
derived roles
AI = read by an AI vision model · DERIVED = a computed estimate, not a direct measurement. The “How we know this” section below details each.
The garden year bloom → fruit → fall colour
J
F
M
A
M
J
J
A
S
O
N
D
Bloom
Fruit
Bloom (the flower's colour) Ripe fruit
Bloom · May — USDA PLANTS (DwCA, Zenodo 17903503) — BloomPeriod
Fruit · approximate season (USDA Seed Period), clamped to after bloom · persists into winter
When to sow · for your area

Sow timing keys off your local last- and first-frost dates.

Species characteristics from USDA PLANTS (public domain) + TRY (CC BY) — general guidance, not a guarantee for your exact site. Deer "browsing" is documented palatability, not a deer-proof claim.

Wildlife & pollinators

How pollinator value is scored →
❧ Caterpillar hosts ~68 caterpillar species

Sorbus supports ~68 caterpillar species.

Native butterfly & moth caterpillars are the base of the terrestrial food web — most songbirds rear their young almost entirely on them. As a host for native Lepidoptera this is a strong genus.

Recorded feeding on Sorbus in North America, including:

Acleris laterana · leafroller moth Acleris nivisellana · Snowy-Shouldered Acleris Acrobasis tricolorella · Tricolored Acrobasis Moth Acronicta americana · American Dagger Moth Acronicta barnesii · owlet moth Acronicta clarescens · Clear Dagger Moth
+ 8 more species →
Acronicta fragilis · Fragile Dagger Moth Acronicta grisea · Gray Dagger Acronicta interrupta · Interrupted Dagger Acronicta pruni · owlet moth Acronicta radcliffei · Radcliffe's Dagger Moth Acronicta superans · Splendid Dagger Alsophila pometaria · Fall Cankerworm Amphipyra pyramidoides · Copper Underwing
Keystone count (genus-level) from Warren II 2026 (CC0) · Tallamy host-use records. Named species (a documented Nearctic sample, not exhaustive) from NHM HOSTS (CC0).
Species thumbnails re-hosted from iNaturalist — Creative Commons, credited per image (hover for credit). Click any species to see it on iNaturalist. Not exhaustive; many taxa have no openly-licensed photo yet.
How we know this (1) Methods & honest limits
Mature width Derived

For woody plants that have a height but no measured crown, we estimate width = height × a crown-to-height ratio fit for that plant’s form (conifers narrower than broadleaf trees, shrubs widest), calibrated on our measured open-grown crowns and capped at the largest one ever measured. A measured crown always wins; herbaceous plants get nothing (no anchor).

Honest limits: A coarse class-median estimate for garden-scale spacing, not a measurement; woody single/multi-stem forms only.

Allometric basis: Jucker et al. 2022 (Tallo); Pretzsch et al. 2015; McPherson et al. 2016 (USDA Urban Tree DB).
Derived values are computed from open data by a published method — labelled, cited, and never shown as a direct observation. Full methodology →
Sources for this entry (24) Open & cited
[01] Scientific name & family — USDA PLANTS (DwCA, Zenodo 17903503)
[02] Growth habit & duration — USDA PLANTS (DwCA, Zenodo 17903503)
[03] Native status & distribution — USDA PLANTS (DwCA, Zenodo 17903503)
[04] Common name — USDA PLANTS (via GBIF)
[18] Invasive / introduced status — USDA PLANTS (DwCA, Zenodo 17903503) — native status
[19] Ecological value — Warren II 2026 (CC0) · Tallamy host-use counts
[20] Conservation rank — NatureServe Explorer (CC BY)
[22] Caterpillar host count — Warren II 2026 (Dryad, CC0) · Tallamy host-use counts
[23] Caterpillar species — NHM HOSTS (CC0)
Spot an error or have a better photo? Every field links to its source, and the whole dataset is open.
Cite this page Open data, please attribute

PlantKey’s data is open under CC BY-SA 4.0 — free to reuse and adapt, with attribution and the same licence. Photos keep their own per-image licence + credit (see Sources above).

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