Ranging from a large shrub to a medium sized tree, thinleaf alder has red and golden pendent flowers (catkins), green and gray foliage and persistent fruit nutlets and smooth bark that make it interesting even in winter. A deciduous large shrub to small tree depending on severity of winter or availability of soil moisture, this species is native to Europe and the Caucausus as well as in North America from California to Canada and across the northern United States. The bark is usually smooth and gray, brown or sienna in color but in age can become more platy.
In late winter to early spring, clusters of catkins (or drooping, finger-like flower strands) appear before the leaves. These more obvious reddish to golden brown catkins are the male flowers and will be pollinated by the wind. The less obvious female catkins are borne nearby. The females develop oval fruits that are green and the turn brown and linger over the winter, not to open and shed the seeds until the next summer. After flowers, the leaves emerge. They are oval and medium to dark green with teethed edges and a hairy, grayish underside. The veins in the leaves are obvious, too.
Grow thinleaf alder in full sun to partial shade in average to nutrient depleted soils that are moist to wet. Often used to help in restoration plantings, this tree is tolerant of cold. dry soil and moderate drought. It can be used as a fast-growing shade tree or an effective windbreak.
Information source: www.Learn2Grow.com.
Genus - Alnus
Species - Incana
Common name - Thinleaf Alder
Pre-Treatment - Required
Hardiness zones - 2 - 6
Height - 20'-70' / 6 - 20 m
Spread - 12'-30' / 4 - 9 m
Plant type - Medium Tree
Vegetation type - Deciduous
Exposure - Full Sun, Partial Shade
Growth rate - Fast
Soil PH - Acidic, Neutral, Alkaline
Soil type - Clay, Loam
Water requirements - Wet soil
Landscape uses - Screening / Wind Break, Shade Trees, Street Trees
Bloom season - Late winter - early spring
Leaf / Flower color - Green / --
Seeds of alder requires 60 days cold moist stratification for best germination.
Stratification/ cold treatment: mix together equal amounts of sand and peat in a small container and moisten it with a little water. Mix the seeds in the medium and place it in the fridge at +2C (40F).
Keep the medium moist throughout the stratification period.
After stratification sow 3 mm (1/8") deep, keep moist at room temperature in the light place.
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