Alnus or Alder trees boast attractive serrated leaves, with some varieties also offering decorative catkins and small cones. Alder trees are popular with wildlife including bees and are renowned for improving the fertility of soil. They're also great for difficult positions, including damp or wet sites.
Alder, or Alnus to use its Latin name, is a small genus of about 30 species of tree and shrub. They belong to the Betulaceae family along with Birch trees and, like Birch, they feature catkins. Alder trees are monoecious, so both the male and female catkins are found on each tree. The male catkins are long and hang down, whilst the female catkins open like Coniferous cones. The catkins are of value to wildlife, providing nectar early in the season for bees and the seeds being popular with birds including goldfinch.
Mainly deciduous, the leaves are serrated to varying extents. Alnus incana 'Laciniata' and Alnus glutinosa 'Imperialis' are Cut Leaved varieties that feature ornate, deeply serrated leaves.
Commonly found near water in the wild, Alder trees are particularly hardy and great for difficult sites from poor soil to damp conditions and wind exposure.
Alder trees are commonly planted for their nitrogen fixing properties. The root nodules of Alnus plants contain a nitrogen fixing bacterium which absorbs nitrogen from the air and makes it available to the plant. The alder plant then provides the bacterium with sugars which it produces through photosynthesis. This mutually beneficial relationship allows alder trees and shrubs to improve the quality of the surrounding soil. When used as a pioneer species (hardy plants used to colonise previously damaged areas) Alder provides additional nitrogen to the successional plants that follow.
An Alder tree features in the coat of arms for the Austrian town of Grossari and the wood of Alder trees has been used for many years in different cultures. Alder wood is commonly used for making furniture including cabinets and since the 1950s, it has been used to make electric guitars as the wood is said to give an even, balanced tone. Alder wood is also used for smoking food, especially seafood e.g. salmon. Although the catkins are edible they are not particularly enjoyable but can come in handy for survival purposes!