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California Alder

Alnus rhombifolia

tree View on Calscape

Care

Sun

full sun, part shade

Water

high

Soil

Fast, Medium, Slow; Tolerant of sand and clay.

Size

49–82ft tall , 35–35ft wide

Bloom

Jun-Nov

Foliage

Deciduous

Keystone Plant

Supports up to 202 butterfly and moth species in Mediterranean California

Native Range

Riparian corridors throughout California from sea level to 6000 ft elevation, along streams and rivers in valleys, foothills, and mountains from Oregon to Baja California.

Care Guide

Planting

Plant your California alder in full sun to part shade in a location with moist soil - it thrives in riparian areas and wet spots where other trees struggle. It tolerates sand, clay, and various drainage rates (fast to slow), so soil type is flexible. Space it away from structures and underground pipes, as its roots can be invasive; this tree is best suited to larger properties, woodland plantings, or naturalized areas rather than small residential gardens. Plant in fall or winter when the tree is dormant for best establishment.

After Planting

Water deeply and keep the soil moist through your first summer and into the second growing season - this is critical for establishment. Once established, your alder is heat and wind tolerant and will need less frequent watering, though it still prefers consistently moist conditions. Expect vigorous growth and a deciduous canopy that drops in winter; the tree will produce showy male catkins in early spring before leaves emerge, followed by small cone-like female catkins in fall that may persist through the year. The most common mistake is underwatering during establishment - this fast-growing native needs consistent moisture in its first year to develop the deep root system it needs.

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