Grey alder
Alnus incana · Betulaceae
📷 Nikanos · CC BY-SA 2.5
The gardener's calendar
In autumn, ease off feeding and take the chance to clean up around grey alder and prepare for winter.
ID card
- Scientific name
- Alnus incana
- Family
- Betulaceae
- Type
- Deciduous tree
- Adult height
- 18 to 20 m
- Spread
- 10 to 12 m
- Growth
- Fast
- Flowering
- March to April (catkins)
- Hardiness
- Very hardy (zone 2-8)
- Origin
- Europe, Northern Asia
✓ Taxonomy verifiedSource: AI estimate · hardiness: reliability high.
Expert tips
The key tip
White alder tolerates poor, compacted, or even temporarily waterlogged soils. Extremely hardy and undemanding, it thrives at the forest edge or in regeneration areas.
The common mistake
Overwatering or over-amending it: it becomes soft and prone to disease.
The pro's trick
Collect the cones at maturity (autumn), dry them for 2 weeks.
Care
Sunlight
Grey alder develops best in full sun, though it tolerates partial shade. Planted in an open location, it will benefit from better growth and denser branching. Avoid heavily shaded areas that would slow its development.
Watering
This tree particularly loves moist soils and environments near water (riverbanks, marshy areas). Keep the soil regularly moist, especially during the first years after planting. Once established, grey alder is very tolerant of persistent moisture and even temporary flooding.
Soil and planting
Grey alder adapts to most soil types, including poor, acidic and compacted soils. It nevertheless prefers moist, well-drained ground. This tree is excellent for stabilizing banks and improving degraded soils thanks to its ability to fix atmospheric nitrogen through its roots.
Pruning and training
Pruning is generally not necessary if the tree develops in open space. You can remove dead or misaligned branches in late winter (January-February). To form a compact shape, intervene preferentially after flowering.
Fertilization
Grey alder doesn't need regular fertilizing. Its symbiotic root system allows it to fix nitrogen from the air. An application of compost or organic matter at planting time is generally sufficient to ensure good establishment.
Diseases and pests
Grey alder is generally very robust. However, watch for canker or phytophthora in cases of prolonged excess moisture. Scale insects and aphids may occasionally affect it but rarely seriously. Maintain good drainage to prevent fungal problems.
Did you know?
Grey alder is a remarkable pioneer tree: its knotted roots house symbiotic bacteria (Frankia) that capture nitrogen from the atmosphere, enriching even the poorest soils. This is why you'll often find it as the first species to colonize degraded land and restored mining areas, preparing the ground for other species. In the Middle Ages, alder wood was prized for foundation piles because it resists rot remarkably well in wet or submerged environments.
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
- Dwarf birchBetula nana
- European Hop-hornbeamOstrya carpinifolia
- Turkish hazelCorylus colurna
- Italian AlderAlnus cordata
- River birchBetula nigra
Tips generated and checked by Viridia — adapt them to your local climate.