Alnus rhombifolia is a medium-sized deciduous tree growing to 49-82 ft rarely to 115 ft tall, with pale gray bark, smooth on young trees, becoming scaly on old trees.
The flowers are produced in catkins. The male catkins are pendulous, yellowish, and produced in clusters of two to seven; pollination is in early spring, before the leaves emerge. The female catkins are ovoid, when mature in autumn and resemble a small conifer cone. The small winged seeds disperse through the winter, leaving the old woody, blackish ‘cones’ on the tree for up to a year after.
The White Alder is closely related to the Red Alder (Alnus rubra), differing in the leaf margins being flat, not curled under. Like other alders, it is able to fix nitrogen atmospheric nitrogen, and tolerates infertile soils.
If used domestically they should be planted well away from drainpipes, sewage pipes, and water lines, as the roots may well invade and clog the lines. These fast-growing trees often grow 3 ft. per year until 20 years of age. They are a relatively short lived species compared to other PNW native tree species.
