thinleaf alder
Alnus incana · Betulaceae
thinleaf alder (Alnus incana) is a perennial tree in the Betulaceae family. It is native to North America. USDA records it as hardy in zone 1 and warmer, down to about -62°F.
At a glance
| Type | tree Derived |
|---|---|
| Lifecycle | perennial USDA |
| Native status | native USDA |
| Mature height | 20 ft USDA |
| Light | part-shade USDA |
| Water need | high USDA |
| Growth rate | rapid USDA |
| Soil pH | 5.5–7 USDA |
| Bloom | March–April USDA |
| Flower color | Purple USDA |
| Hardiness zones | 1 and warmer USDA |
| Guild layer | understory Derived |
| Nursery availability | Routinely Available USDA |
USDA quoted from the USDA PLANTS database · Derived computed by a fixed rule from those columns. No value on this page is estimated.
Growing conditions
It grows in partial shade. USDA rates it as having needs consistently moist ground. Its drought tolerance is rated low. It tolerates saturated, poorly drained ground well (USDA rates its anaerobic tolerance high). It is recorded on soils from pH 5.5 to 7 — a broad range that spans acidic through mildly alkaline ground. Its cold limit is zone 1.
Size and growth
At maturity it reaches about 20 ft, making it a small tree or large shrub. It grows quickly.
Bloom period
USDA records a bloom period of March through April. Flowers are purple.
A flowering date, not a pollinator rating.
Foliage, flower and season
Summer foliage is dark green, medium in texture. Its flowers are not conspicuous — a plant for form and foliage. Its active growth period is spring and summer. USDA rates its lifespan as moderate.
What the site needs to provide
USDA records it across sites receiving 10 to 20 inches of annual precipitation. The low end of that band is genuinely arid, so it has a wide tolerance for dry country. It needs at least 130 frost-free days to finish its season. It roots to at least 18 inches. Fertility requirement: medium.
Propagating it
Propagate it from seed, bare root and container stock. Seed needs cold stratification — a period of moist chilling — before it will germinate, so sow in autumn or chill it artificially before a spring sowing. Its seed spreads at a moderate rate. It spreads vegetatively at a slow rate.
Resilience and wildlife
Browsing animals rate it barely palatable — the sourced basis for calling it deer-resistant. Its fire tolerance is rated medium, and it can resprout after damage. Its growth form is recorded as thicket forming.
Role in a guild
Understory. In a layered planting this is the layer beneath the canopy, tall enough to hold structure but shaded from above. The layer is derived by a fixed rule from growth habit and mature height.
Tags
Related plants
Others in Alnus
- European alder Alnus glutinosa
- gray alder Alnus incana
- speckled alder Alnus incana
- seaside alder Alnus maritima
Similar role and hardiness
- Tilesius' wormwood Artemisia tilesii
- water birch Betula occidentalis
- apple Malus mill
- sandbar willow Salix interior
Where this data comes from
Every value on this page comes from the USDA PLANTS database record for symbol ALINT, or is computed from those values by a fixed rule. Nothing here is estimated or model-generated. Where USDA publishes no value, this page omits the claim rather than filling the gap.
- Quoted from USDA PLANTS: active growth period, Bloom, Bloom end, browse palatability, cold stratification, Drought tolerance, fall conspicuous, fertility requirement, fire tolerance, Flower color, flower conspicuous, foliage color, foliage porosity winter, foliage texture, frost free days min, fruit conspicuous, growth form, Growth rate, Hardiness zones, Lifecycle, lifespan, Light, Mature height, Minimum temperature, Native status, Nitrogen fixation, Nursery availability, precipitation max in, precipitation min in, propagation, resprout ability, root depth in, seed spread rate, Soil pH, Soil pH (upper), Tolerance of wet soil, Toxicity, vegetative spread rate, Water need.
- Derived by a fixed rule from those columns: Guild layer, Type.
Read our full data sources and methodology.
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