Description
Alnus – Alder
There are about 35 species, occurring in cold to cool temperature regions in the Northern Hemisphere in this genus. They are deciduous, semi evergreen-to-evergreen trees, which are fast growing and can be short, lived. They’re unique for carrying microorganisms in their roots that can turn air into nitrogen to fix depleted soils. They bear alternate leafs larger and thicker then the Birch’s which they are closely related, with smooth and wavy to jaggedly toothed edges. Flowers are tiny but arranged in catkin (dense cluster of scale like flowers as of a Birch), male catkins are long and thin hanging in profuse bunches at the ends of branches, female catkins are short and barrel-shaped in less conspicuous groups. The bark is brown or blackish and sometimes wrinkled. Used as a shade tree or nurse tree or a windbreaker. They have little fall colors.
Sun loving trees that likes moist soils such as bottom of the valleys or were soil is too waterlog or that are very infertile or polluted.
Should be pruned early to a single truck and trim branches above head height.
Prone to Phytophtora root rot and mealybugs.
Alnus tenuifolia – Mountain Alder – Thinleaf Alder – This tree found in Western North America, from British Columbia to California grows into small spreading tree reaching 25’ feet tall and in breadth with a rounded head. Young shoots are red and downy but soon become smooth carrying egg shape 4” long dark green above and with paler undersides. Pendent clusters of 3-4 yellow brown male catkins to 2 ½” long opening in early spring before the leaves.
Zones 3-9
