Alder
Alnus
Alders (Alnus) are deciduous trees and large shrubs of the birch family, native mainly to moist woodland and stream banks in the northern hemisphere. They grow quickly, often with a pyramidal outline, bear hanging catkins in early spring and small woody cones that stay on the branches through winter. Their roots fix nitrogen and so enrich the soil.
Common alder
Alnus glutinosa
Common or black alder (Alnus glutinosa) is native to almost all of Europe and grows naturally along water. It becomes a sturdy, sometimes multi-stemmed tree that can exceed 20 m. The rounded, blunt-tipped leaves and the violet-grey buds feel sticky when young. Yellow-brown male catkins open in March and April, and the small cones remain well into winter.
Location and soil
Thrives in moist to wet, poor and even waterlogged soil, preferably slightly acid, in sun or light shade; its tolerance of drought is limited. Extremely hardy and little affected by wind, including sea wind. The strong, fairly deep roots dislike paving and can block drains, so plant it well away from buildings and pipes.
Pruning and care
Water during the first season; afterwards little care is required. Prune at the end of winter, in February and March. The tree takes hard pruning well and resprouts readily from the stump, so it can be coppiced. On constantly waterlogged sites, keep an eye out for alder dieback.
Use in the garden
Widely used to secure the banks of streams, ditches and ponds, in wet woodland and landscape planting, and as a nurse tree that improves the soil by fixing nitrogen. Also suitable as a solitary, avenue or group tree in larger gardens. Its wood barely rots under water and was traditionally used for piles and water conduits.
