Red Alder
Alnus rubra
Care
part shade
high
Slow; Tolerates a variety of soils as long as adequate moisture is available. Tolerates saline soil..
50–98ft tall , 45–45ft wide
Jan-Dec
Deciduous
Supports up to 202 butterfly and moth species in Mediterranean California
Riparian forests and wetlands from Humboldt County to Kern County, below 4000 ft elevation along streams and flood zones, extending to British Columbia.
Care Guide
Planting
Plant your red alder in partial shade with plenty of space - this is a large tree that will reach 50–98 feet tall and needs room to spread. Choose a spot with slow-draining soil that stays consistently moist; red alder tolerates a variety of soil types as long as adequate moisture is available. Plant in fall or early winter when the tree is dormant. Avoid planting where you'll be tempted to water shallowly and frequently, as this encourages problematic surface roots.
After Planting
Water deeply and infrequently rather than with frequent shallow watering; this encourages deep roots and prevents surface root issues. Once established, red alder is surprisingly drought tolerant and needs summer irrigation no more than twice a month. The Calscape data provided does not include specific pruning recommendations or details about year-one care, so focus on establishing a deep watering pattern and letting the tree develop naturally.
Wildlife Supported
Insects
Forms critical nitrogen-fixing nodules in alder root systems; essential for riparian soil health
Larvae feed on alder foliage; overwinter as pupae
Nocturnal larvae feed on alder foliage
Pollen from catkins provides early season protein source
Adult beetles skeletonize alder leaves in mid-summer
Hairy caterpillars feed on alder foliage
Mammals
Preferred food and construction material; critical riparian resource
Spring diet includes emerging alder catkins and young foliage; early green food
Birds
Irruptive winter visitor; feeds on alder seeds
Resident; forages for small insects on alder foliage and twigs
Harvests alder seeds in late fall and winter
Year-round resident in California; harvests alder seeds fall-winter
Forages on bark and foliage for insects; resident in alder riparian zones
Migrant; forages on insects in alder canopy during breeding season arrival