Alnus incana (Mountain Alder, Gray, Speckled Alder, or Thin Leafed Alder) is a fast-growing, multi-stemmed deciduous tree or large shrub. Known for its symbiotic nitrogen-fixing root nodules and decorative, gray, speckled bark, it serves as a vital ecological pioneer in riparian zones and disturbed wetland environments.
Grows in USDA zones 2 – 6. It thrives in cold to cool climates and generally does not perform well in the heat south of Zone 6. Will grow in Zone 7 and 8 in the West Coast if planted in afternoon shade in a in wetland or streambank locations.
In zone 2-6 prefers full sun to partial shade. It avoids and performs poorly in deep, full shade.
Highly adaptable to soil conditions, but thrives in heavy, medium-to-wet, and mucky soils. Tolerates poor and compacted soils well. It requires consistently moist to wet ground and has a high tolerance for seasonal flooding. Prefers acidic soils.
Typically grows between 15 to 40 feet tall and 15 to 35 feet wide, frequently forming dense, thicket-like colonies.
Uses
- Erosion Control & Soil Health: Its shallow, extensive root system makes it an excellent choice for stabilizing pond margins, streambanks, and flood-prone areas. The root nodules fix atmospheric nitrogen, improving soil fertility for surrounding plants.
- Land Reclamation: Acts as an excellent pioneer species to re-establish woodlands on difficult sites, disused farmland, or compacted soils.
- Wildlife Habitat: Provides heavy cover for birds and mammals; catkins and seeds act as a crucial winter food source for birds like finches, and the leaves are browsed by deer, moose, and beaver.
- Woodwork & Craft: Produces light, soft wood often used for carving, bowls, woodcuts, and fuel. The bark and fruit contain tannin and have historically been used for dyes and tanning leather.
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