Alphabetical Plant Listing

Alnus rubra (Red Alder)

Red Alder, Western Alder, Oregon Alder, Pacific Coast Alder, Alnus oregona, Alnus oregona var. pinnatisecta


Fast-growing, Alnus rubra (Red Alder) is a medium-sized deciduous tree of graceful habit with a straight trunk, and a pointed or rounded crown with rather pendulous branches. The thin bark is smooth, mottled, light gray to whitish, and often covered with green moss. The wood, when bruised, turns a rusty red color, which is how the tree gets its name. The foliage of ovate, dark green leaves is rust-colored and hairy beneath, with coarsely toothed margins that are rolled under. In early to mid spring, long, pendant, chartreuse-brown male catkins, 5 in. long (12 cm), dangle like Christmas decorations near the bare branch tips. The catkins release clouds of pollen that attract bees and other insects. Inconspicuous female flowers in the form of erect catkins turn woody and conelike at maturity. They are followed by small, barrel-shaped, dark brown, fruiting cones containing winged seeds (nutlets). Resembling miniature pine cones, they persist on the twigs into winter for a unique and lovely display - to the delight of birds. Native to the Pacific Coast region from southeast Alaska to southern California, Red Alder is also found growing along streams in northern Idaho. Red Alder is the largest American Alder. It grows in climates varying from humid to super-humid with rainy winters and generally cool and dry summers. Red Alder is useful for erosion control on steep slopes where the soil has been disturbed. Its roots contain nitrogen-fixing nodules that can increase the nitrogen in the soil where it is planted. This makes it a very useful conservation tool by increasing the amount of nitrogen available in forest ecosystems or degraded areas. Red Alder is a reliable species for coastal gardens and tolerates brackish water. An intermediate source of food for wildlife, Alders support 255 species of caterpillars as well as many sawfly larvae. This allows a grove of Alder to provide food and shelter for wintering birds, breeding birds, and migrant birds.

  • Grows up to 40-50 ft. tall (12-15 m) and 20-30 ft. wide (6-9 m).
  • Performs best in full sun to full shade in moderately fertile, moist but well-drained soils. Tolerates a variety of soils as long as adequate moisture is provided. Tolerates saline soils.
  • Good choice for hedges and screens, wildlife gardens.
  • No serious pest or disease issues. Keep an eye out for phytophthora root rot.
  • Requires minimal pruning.
  • Propagate by seed in a seedbed as soon as ripe. Root hardwood cuttings in winter and softwood cuttings in summer. Bud grafting can be performed in late summer .
  • Native to western North America including Alaska, British Columbia, Washington, Oregon, California, and Idaho.

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Requirements

Hardiness 5 – 10
Climate Zones 3, 4, 5, 6, 7, 14, 15, 16, 17
Plant Type Trees
Exposure Full Sun, Partial Sun, Shade
Season of Interest Spring (Early,Mid,Late)
Summer (Early,Mid,Late)
Fall
Winter
Height 40' – 50' (12m – 15m)
Spread 20' – 30' (6m – 9m)
Water Needs Average, High
Maintenance Low
Soil Type Chalk, Clay, Loam, Sand
Soil pH Acid, Alkaline, Neutral
Soil Drainage Moist but Well-Drained
Characteristics Showy, Fruit & Berries
Native Plants United States, Alaska, California, Pacific Northwest, Idaho, Oregon, Washington
Tolerance Salt
Attracts Birds, Butterflies
Garden Uses Hedges and Screens
Garden Styles Coastal Garden, Informal and Cottage, Prairie and Meadow

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Carolina K. Smith MD, Serrgey75, MarjanCermelj, Shutterstock, Noel Zia Lee,Gertjan van Noord, Rosewoman, Flickr

While every effort has been made to describe these plants accurately, please keep in mind that height, bloom time, and color may differ in various climates. The description of these plants has been written based on numerous outside resources.


Requirements

Hardiness 5 – 10
Climate Zones 3, 4, 5, 6, 7, 14, 15, 16, 17
Plant Type Trees
Exposure Full Sun, Partial Sun, Shade
Season of Interest Spring (Early,Mid,Late)
Summer (Early,Mid,Late)
Fall
Winter
Height 40' – 50' (12m – 15m)
Spread 20' – 30' (6m – 9m)
Water Needs Average, High
Maintenance Low
Soil Type Chalk, Clay, Loam, Sand
Soil pH Acid, Alkaline, Neutral
Soil Drainage Moist but Well-Drained
Characteristics Showy, Fruit & Berries
Native Plants United States, Alaska, California, Pacific Northwest, Idaho, Oregon, Washington
Tolerance Salt
Attracts Birds, Butterflies
Garden Uses Hedges and Screens
Garden Styles Coastal Garden, Informal and Cottage, Prairie and Meadow

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