Native Plant of the Month: Red Alder

Photo of Red Alder.

Common Name: Red Alder 

Binomial Name: Alnus rubra 

Soil Type: Adaptable to Most 

Sunlight: Full to Part Sun 

Form/Growth: Pyramidal, often with Multi Leaders

 Plant Type: Broadleaf 

Foliage: Deciduous 

Flowering: Yes - Catkins 

Getting its name from the reddish color that develops when its bark is bruised or scraped, the red alder is one of Oregon’s prominent natives. It is the largest species of alder in North America and one of the largest in the world, reaching heights of 80 – 120 ft. The official tallest red alder resides right here in Oregon (Clatsop County), standing at an astonishing 128 ft. tall! 

Red alder leaves are egg or oval shaped, have bluntly serrated edges with a distinct point at the end, and are bright to dark green, turning yellow in the fall. Their flowers are actually reddish catkins, slim, cylindrical flower clusters. The female flowers develop into small, woody, cone-like fruit. 

In moist areas, red alders will rapidly cover burn or clear-cut areas, temporarily preventing other conifers from growing. During this time, the red alders improve the soil fertility for future growth of conifers. This impressive native is also very valuable for playing host to the nitrogen-fixing bacteria, Frankia, allowing alders to grow in nitrate-poor soils. 

This Native Plant of the Month has been brought to you by the City of Beaverton’s Landscape and Urban Forestry.