# Red alder (Alnus rubra)

> The largest North American alder and the Northwest's main hardwood: a fast, straight tree with smooth mottled gray bark (often painted with white lichen), serrated leaves with rolled-under edges that drop green, reddish catkins in late winter and small woody cones that hang on all winter. Root nodules fix nitrogen, so it rebuilds poor and disturbed soils and is widely used for streambank and mine-site restoration. It is short-lived and heart rot sets in after about 60 years.

Source: https://treerm.org/trees/alnus-rubra · Updated 2026-11-08 · License CC BY 4.0

## Facts

- Also called: Oregon alder, Western alder
- Family: Betulaceae
- Type: Broadleaf, drops leaves
- Mature height: 25 m; spread 12 m
- Growth: Fast growing; lives about 60 years
- USDA hardiness zones: 5 to 8
- Light: Sun or part shade
- Water: Moderate water
- Soil: Wet to well-drained gravels, sands, clays and poor soils; fixes its own nitrogen
- Native range: Pacific coast from southeast Alaska through British Columbia, Washington and Oregon to central California, nearly always within about 200 km of the ocean, with inland pockets in Idaho and Montana.

**Benefits:** Fixes nitrogen, Fast canopy, Holds soil, Flood tolerant, Wildlife, Birds, Stores carbon well

**Good for:** Streambanks, Reforestation, Timber, Agroforestry, parks

**Watch out for:** Short lived, Allergenic pollen

## Care

Plant in full sun or part shade in moist soil; it tolerates flooding and some drought once established. Little pruning is needed beyond removing dead wood in dormancy. Tent caterpillars, alder flea beetle and sawflies defoliate but rarely kill; avoid wounding the trunk, which lets heart rot in.

## Where it stands

- **Native:** BC, Canada; YT, Canada; AK, United States (Southeast Alaska.); CA, United States (Coast south to central California.); ID, United States (Inland pockets.); MT, United States (Northernmost Montana.); OR, United States; WA, United States

## Sources

- https://plants.ces.ncsu.edu/plants/alnus-rubra/
- https://plants.usda.gov/plant-profile/ALRU2
- https://en.wikipedia.org/wiki/Alnus_rubra