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Oregon Alder Alnus rubra

Description

Red alder is a deciduous tree in the Betulaceae (birch) family.  It is native to the western coast of North America from Alaska down to California. This is one of the larger alders and grows 65-98 feet tall. It gets its name from the orange/red underbark that was used to make dye by Native Americans.

This tree can be distinguished from other alders by the rolled under margins of the leaves, the stalked buds and impressed veins on the underside of the leaves. Red Alder is able to grow in poor soils due to its association with the soil bacterium, Frankia, which allows it to fix nitrogen. Because of this, they are often used in land reclamation projects. 

This tree grows fairly fast and will spread by seed. It tolerates soils ranging from well-drained gravels and sands to poorly drained clay or organic soils. It will grow in full sun to partial shade and prefers cool wet winters and warm dry summers.

Insects, Diseases, and Other Plant Problems:  Red alder is fairly free from most insect and disease problems, especially when young (age 40 or 50) and uninjured. Phellinus igniarius, a white heart rot, is probably the major cause of cull in older trees. The forest tent caterpillar (Malacosoma disstria), western tent caterpillar (M. californicum), alder woolly sawfly (Eriocampa ovata), striped alder sawfly (Hemichroa crocea), the alder flea beetle (Altica ambiens), and a leaf beetle (Pyrrhalta punctipennis) have caused substantial damage but rarely kill the tree.

VIDEO created by Ryan Contreras for “Landscape Plant Materials I:  Deciduous Hardwoods and Conifers or Landscape Plant Materials II:  Spring Flowering Trees and Shrubs” a plant identification course offered by the Department of Horticulture at Oregon State University

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Cultivars / Varieties:
Tags:
#drought tolerant#nitrogen fixation#deer browsing plant#poor soils tolerant#deciduous tree#wet soils tolerant#full sun#land reclamation#landscape plant sleuths course
 
Cultivars / Varieties:
Tags:
#drought tolerant#nitrogen fixation#deer browsing plant#poor soils tolerant#deciduous tree#wet soils tolerant#full sun#land reclamation#landscape plant sleuths course
  • Attributes:
    Genus:
    Alnus
    Species:
    rubra
    Family:
    Betulaceae
    Uses (Ethnobotany):
    A russet dye was made from the bark. Native Americans also used the bark to treat various illnesses. The wood is used for furniture and cabinets.
    Life Cycle:
    Woody
    Country Or Region Of Origin:
    Western North America
    Distribution:
    Alaska, Yukon, British Columbia, Washington, Oregon, California, Idaho and Montana
    Wildlife Value:
    Deer and elk will browse the twigs and finches will eat the seeds
    Play Value:
    Wildlife Cover/Habitat
    Wildlife Food Source
    Dimensions:
    Height: 66 ft. 0 in. - 98 ft. 0 in.
    Width: 35 ft. 0 in. - 50 ft. 0 in.
  • Whole Plant Traits:
    Plant Type:
    Tree
    Woody Plant Leaf Characteristics:
    Deciduous
    Habit/Form:
    Conical
    Erect
    Growth Rate:
    Rapid
    Maintenance:
    Medium
    Texture:
    Medium
  • Cultural Conditions:
    Light:
    Full sun (6 or more hours of direct sunlight a day)
    Partial Shade (Direct sunlight only part of the day, 2-6 hours)
    Soil Texture:
    Clay
    Loam (Silt)
    Sand
    Shallow Rocky
    Soil Drainage:
    Good Drainage
    Available Space To Plant:
    24-60 feet
    USDA Plant Hardiness Zone:
    5b, 5a, 6b, 6a
  • Fruit:
    Fruit Color:
    Brown/Copper
    Fruit Type:
    Samara
    Fruit Length:
    < 1 inch
    Fruit Width:
    < 1 inch
    Fruit Description:
    Produces small brown cone-like strobiles less than an inch long that stay on the tree throughout winter. Seeds are winged samaras.
  • Flowers:
    Flower Color:
    Red/Burgundy
    Flower Inflorescence:
    Insignificant
    Flower Bloom Time:
    Spring
    Flower Description:
    Male catkins are reddish and 4-6 inches long. Female catkins are cone-like and woody, oval
  • Leaves:
    Woody Plant Leaf Characteristics:
    Deciduous
    Leaf Color:
    Green
    Deciduous Leaf Fall Color:
    Gold/Yellow
    Leaf Type:
    Simple
    Leaf Arrangement:
    Alternate
    Leaf Shape:
    Ovate
    Rhomboidal
    Leaf Margin:
    Serrate
    Hairs Present:
    Yes
    Leaf Length:
    3-6 inches
    Leaf Width:
    1-3 inches
    Leaf Description:
    2.5-6 inch long green leaves are ovate with a pointed apex. The serrated margins are revolute or curled under and the veins are impressed especially on the undersides. Hairs are present on the undersides. They turn yellow in the fall.
  • Bark:
    Bark Color:
    Light Gray
    Bark Description:
    The bark is mottled, ash-gray and smooth, often colonized by white lichen and moss. When bruised or scaped it has a rusty red color.
  • Stem:
    Stem Color:
    Brown/Copper
    Green
    Stem Is Aromatic:
    No
    Stem Buds:
    Hairy
    Stem Bud Scales:
    Enclosed in 2 scales
    Stem Cross Section:
    Angular
    Stem Lenticels:
    Conspicuous
    Stem Description:
    Olive to reddish-brown twigs are triangular in cross-section, the buds are distinctly stalked and have 2-3 pubescent scales, lenticels are prominent.
  • Landscape:
    Landscape Location:
    Lawn
    Riparian
    Landscape Theme:
    Water Garden
    Attracts:
    Small Mammals
    Songbirds
    Resistance To Challenges:
    Drought
    Humidity
    Poor Soil
    Wet Soil