Red alder
Alnus rubra · Betulaceae
📷 Walter Siegmund · CC BY 2.5
The gardener's calendar
In autumn, ease off feeding and take the chance to clean up around red alder and prepare for winter.
ID card
- Foliage
- Deciduous
- Blooming
- Spring (March to May)
- Adult size
- 49 to 82 feet tall
- Growth
- Fast
- Hardiness
- Very hardy (-4°F and below)
- Origin
- West coast of North America
- Soil type
- Moist, poorly drained, acidic
✓ Taxonomy verifiedSource: AI estimate · hardiness: reliability high.
Expert tips
The key tip
Red alder is a living fertilizer machine that enriches soil, but demands consistent moisture: plant it at the base of a slope, near a retention pond, or in regularly flooded zones. It thrives where others drown in excess water.
The common mistake
Planting it in dry soil or on a ridge thinking it's 'just an ordinary hardy tree'.
The pro's trick
Leave some natural shoots if you want to densify a wet zone quickly.
Care
Watering
Red alder appreciates constantly moist to wet soil. Water regularly during the growing season, especially during dry summers. This tree tolerates wet areas and marshland well, even temporarily flooded terrain.
Light Exposure
Choose a location in full sun for optimal growth and dense branching. Red alder tolerates partial shade but develops less vigorously. Avoid overly shaded areas that slow its growth.
Pruning and Structure
Requires minimal pruning once established. Remove dead or poorly oriented branches in late winter. Lightly thin the crown if needed to promote better branching and foliage aeration.
Soil
Red alder prefers acidic to neutral soil, rich in organic matter and with good moisture content. It adapts to poor and compacted soils, making it ideal for reclaiming degraded or wet areas. Amend with compost at planting time.
Fertilization
Not demanding in nutrients thanks to its symbiosis with nitrogen-fixing bacteria. An annual application of well-decomposed compost is sufficient. Avoid excessive mineral fertilizers that could promote unbalanced rapid growth.
Diseases and Pests
Generally robust and relatively insensitive to diseases. Occasionally watch for aphids or scale insects in case of water stress. Powdery mildew can appear in very humid conditions; good air circulation prevents this issue.
Did you know?
Red alder is a natural colonizer of degraded areas: its roots harbor bacteria (Frankia) that fix nitrogen from the air and enrich the soil. Native Americans and Alaska peoples used its bark to dye clothes reddish-brown, which is how it got its name. This tree can live 50 to 100 years and plays a key role in ecological restoration of disturbed habitats.
Where to buy it
Best planted in autumn so the roots settle in before summer, or in early spring once the frost has passed. Pick a plant with healthy foliage and roots that are not exposed. Best time: March, October, November.
Add this plant to my garden →Plants from the same family
- Silver birchBetula pendula
- Grey alderAlnus incana
- Dwarf birchBetula nana
- European Hop-hornbeamOstrya carpinifolia
- Turkish hazelCorylus colurna
- Italian AlderAlnus cordata
Tips generated and checked by Viridia — adapt them to your local climate.