Family: Betulaceae
Common Name: Alder

Native to the cold and cooler areas of the northern hemisphere, alders are slender upright trees which belong to the birch family. They are deciduous. Catkins appear in spring before the leaves. Alders are useful for protecting streams and river banks and as shelter trees against coastal winds. In the past, they were used extensively in shipbuilding. The timber of some species was also used for musical instruments and clogs, and for harbor and estuary piles. They are often found on riverbanks and some will even grow in swampy, salty soils.

Species

A. cordata, Italian alder, zone 6, is a pyramid-shaped tree which grows to 9 m (30 ft). Its shiny, heart-shaped leaves are like those of the silver birch, and the seed pods are like small pine cones.

A. glutinosa, common or black alder, zone 3, can reach a height of 20 m (65 ft). Young growth is sticky and resistant to cold. The male catkins are yellow and the female ones are tiny and upright. The timber of this European species was traditionally used to make clogs and to bind river banks. Cultivars with different leaf colours and shapes can be obtained.

A. incana, gray alder, zone 2, grows to 15 m (50 ft) and is suitable for very wet conditions. The leaves are green on top and grayish on the underside. 'Aurea', golden alder, has pretty yellow shoots and leaves. In the winter the bare stems are an orange-yellow colour.

A. rubra, the American red alder, zone 5, is a fast grower and reaches a height of 22 m (70 ft). In the spring it produces reddish pendulous catkins. The bark is gray-white. It is a good specimen for coastal planting and it is adaptable to both infertile and moist soils.

A. tenuifolia, mountain alder, suitable for zone 2, is a native of North America. It has oval-shaped leaves and grows to 9 m (30 ft).

Cultivation

Alders enjoy moist, cool soils. Propagate from seed dried in autumn and sown in spring. Alternatively, propagate from hardwood cuttings taken in winter and rooted in a garden frame. Large specimens will withstand heavy pruning and can be transplanted during the dormant winter period.

Climate

Zones 2 to 9 depending on the species.