Grey alder

Profile

Family

Betulaceae

Habit

Tree

Height

18 m

Spread

10 m

Growth

very fast

Lifespan

80 years

First yield

after 5 years

Hardiness

zone 2–6

Shade tolerance

partial shade

Soil

Silt, Loam, Clay

Soil moisture

dry – near water

pH

5.6 – 7.6

Synonyms

Betula alnus incana.

Uses

Other uses: This species fixes atmospheric nitrogen and is also tolerant of contaminated soils. It is suitable for land reclamation, especially on coal spoil heaps. It is an excellent pioneer tree species for reforesting wasteland, difficult sites etc. Through its rapid growth it quickly creates sheltered conditions that allow further, more permanent woodland trees to become established. In addition, bacteria on the roots fix atmospheric nitrogen. This not only enables the tree to grow well on nutrient-poor soils, but also makes nitrogen available to other plants nearby. Alders also have a dense leafy crown, whose leaf fall contributes to humus formation in the soil in autumn. Alder seedlings cannot compete well in the shade of woodlands, so this species gradually dies out as other tree species become established. Bark and fruits contain up to 20% tannins. The wood is light, soft, relatively elastic and easy to split. It is used for clogs, bowls, wood carvings etc. and is highly valued by joiners.

Growing

Prefers heavy soils and moist sites. Thrives on heavy clay soils. Tolerates drier soils than many other species in this genus. Tolerates very nutrient-poor sites. This species lives in symbiosis with certain soil micro-organisms. These form nodules on the roots of the plants and fix atmospheric nitrogen. Some of this nitrogen is used by the growing plant, some is available to neighbouring plants.

Propagation

Seed – best sown in a cold frame as soon as ripe, and only lightly covered with soil. Seed sown in spring also germinates well as long as it is not covered. Germination takes place in spring as temperatures rise. Once the seedlings are large enough, prick them out into individual pots. If they have grown sufficiently, they can be planted out into their final position in summer. Otherwise they remain in pots outdoors and are planted out in spring. If you have enough seed, you can sow it thinly in a seedbed outdoors in spring. The seedlings can either be planted out into their final position in autumn/winter, or grown on in the seedbed for another season. Cuttings of mature wood, taken outdoors in autumn after leaf fall and inserted in sandy soil, are also suitable for propagation.

Origin & habitat

Europe. Introduced to Britain.

Mountains, particularly on poor soils.

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