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ALNUS incana

Image of Alnus incana

Jesse Saylor

Family

Betulaceae

Botanical Name

ALNUS incana

Plant Common Name

Thinleaf Alder

Special Notice

This entry has yet to be reviewed and approved by L2G editors.

General Description

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. Two selections are particularly showy: 'Aurea' has yellow-green foliage while 'Pendula' has a gracefully weeping form.

Characteristics

  • AHS Heat Zone

    6 - 1

  • USDA Hardiness Zone

    2 - 6

  • Sunset Zone

    A1, A2, A3, 1a, 1b, 2a, 2b, 3a, 3b, 4, 5, 6, 7, 8, 9

  • Plant Type

    Tree

  • Sun Exposure

    Full Sun, Partial Sun

  • Height

    20'-70' / 6.1m - 21.3m

  • Width

    12'-30' / 3.7m - 9.1m

  • Bloom Time

    Early Spring, Late Winter

  • Native To

    North America, United States, Northeastern United States, Mid-Atlantic United States, North-Central United States, Western United States, Northwestern United States, Southwestern United States, California, Canada, Europe, Northern Europe, Southern Europe, Western Europe, United Kingdom, Turkey, Western Asia

Growing Conditions

  • Soil pH

    Acidic, Neutral, Alkaline

  • Soil Drainage

    Average

  • Soil type

    Clay, Loam

  • Tolerances

    Wet Site

  • Growth Rate

    Medium

  • Water Requirements

    Average Water

  • Habit

    Pyramidal

  • Seasonal Interest

    Spring, Summer, Fall, Winter

Ornamental Features

  • Flower Interest

    Insignificant

  • Flower Color

    Gold, Orange Red, Sandy Brown

  • Fruit Color

    Green, Olive, Brown

  • Foliage Color (Spring)

    Green

  • Foliage Color (Summer)

    Green

  • Foliage Color (Fall)

    Green, Brown

  • Bark Color

    Sandy Brown, Chocolate

  • Fragrant Flowers

    No

  • Fragrant Fruit

    No

  • Fragrant Foliage

    No

  • Bark or Stem Fragrant

    No

  • Repeat Bloomer

    No

  • Showy Fruit

    Yes

  • Edible Fruit

    No

  • Showy Foliage

    Yes

  • Foliage Texture

    Medium

  • Foliage Sheen

    Glossy

  • Evergreen

    No

  • Showy Bark

    Yes

Special Characteristics

  • Bark Texture

    Smooth

  • Usage

    Screening / Wind Break, Shade Trees, Street Trees

  • Sharp or Has Thorns

    No

  • Invasive

    No

  • Attracts

    Birds

  • Self-Sowing

    Yes