Red Alder (Alnus rubra) - How to Grow & Care Guide

Plant Snapshot

Common Name: Red Alder
Latin Name: Alnus rubra
Alternate Names: Pacific alder, Oregon alder
Hardiness Zones: USDA zones 6–9 (typical coastal and lowland range)
Typical Height: 40–80 ft (12–24 m) tall at maturity
Typical Spread: 30–60 ft (9–18 m) crown spread
Bloom Period: Late winter to spring; male and female catkins produced before or with leaf out
Soil Preferences: Prefers moist to wet soils and tolerates poorly drained or rocky ground; grows best in moist, well drained loams and slightly acidic soils
Light Preferences: Full sun to partial shade; fastest growth in full sun but will establish in partial shade
Toxicity: No major human or pet toxicity documented but wood dust or smoke can irritate; confirm with local authorities for ingestion or allergy risks
Propagation: Seed sowing with cold stratification, root or stump sprouts and vegetative suckering; cuttings and nursery methods used for restoration stock

Key Facts

Native deciduous tree of the Pacific Northwest coast
Fast growing and commonly colonizes disturbed and riparian sites
Forms nitrogen fixing root nodules with actinorhizal bacteria
Produces long male and short female catkins before leaf out
Bark smooth and pale when young often becoming reddish or gray with age
Wood used for furniture, cabinetry and smoking foods
Tolerates wet soils and seasonal flooding better than many hardwoods
Relatively short lived compared with many other shade trees

Red Alder (Alnus rubra) is a fast growing deciduous tree native to the Pacific Northwest that fixes nitrogen and readily colonizes moist disturbed sites. It flowers as long male and short female catkins before leaf out in late winter to spring and is commonly used for riparian restoration and quick shade.

Identification

Leaves are simple and deciduous with a rounded to slightly tapered shape and a serrated edge. Bark is smooth and pale when young often becoming reddish or gray with age. Flowers are produced as long male and short female catkins before leaves open in late winter to spring.

Best uses and where to grow

Use Red Alder for riparian buffers soil stabilization and restoration where rapid cover is needed. It thrives in coastal lowlands and moist valleys within USDA zones 6 to 9 and does well on stream banks and other seasonally wet sites that many hardwoods avoid.

Planting and seasonal timing

Plant container or bare root stock during the dormant season in your region to give roots time to establish before summer drought. Timing shifts with latitude and elevation so match planting dates to local frost and soil moisture conditions for best survival.

Soil light and watering

Prefers moist to wet soils and tolerates occasional flooding yet performs best in moist well drained loams with slightly acidic to neutral pH. Give full sun to partial shade for fastest growth. Avoid prolonged drought because growth and survival decline on dry sites.

Maintenance and controlling spread

Red Alder is fast growing but relatively short lived compared with many shade trees and commonly suckers to form multi stem clumps. Control naturalizing by removing unwanted suckers and coppicing stems. Expect faster crown spread on open sites and narrower crowns when grown in shade.

Propagation

Propagate by seed after cold stratification or by using root and stump sprouts for restoration planting. Vegetative suckering and coppice sprouting are common so clonal regeneration provides rapid canopy closure and soil stabilization after disturbance.

Uses and safety

Wood is valued for furniture cabinetry and smoking foods. No major human or pet toxicity is widely reported but wood dust and smoke can irritate sensitive people. If ingestion or allergy is a concern confirm safety with local poison control or extension services.

Frequently asked questions

How fast does Red Alder grow?: Red Alder is fast growing especially in full sun with moist fertile soil. On good riparian sites young trees can add substantial height within a few years though mature size varies by site.
How large does Red Alder get?: Mature height commonly ranges from 40 to 80 feet with a crown spread around 30 to 60 feet depending on soil fertility moisture and whether it forms multiple stems.
When does Red Alder bloom?: It produces male and female catkins in late winter to spring often before leaves emerge. Exact timing moves earlier in coastal lowlands and later inland or at higher elevations.
Can Red Alder tolerate flooding?: Yes it tolerates wet soils and seasonal flooding better than many hardwoods making it suitable for stream banks and other seasonally saturated locations.
How do I control suckers and spread?: Remove unwanted suckers at the base and coppice stems to manage size. Regular removal prevents multi stem clumps and limits naturalizing in managed landscapes.