Common Name: alder
Type: Tree
Family: Betulaceae
Native Range: Japan
Zone: 6 to 10
Height: 10.00 to 30.00 feet
Spread: 10.00 to 30.00 feet
Bloom Time: March to June
Bloom Description: Female catkins mature from red to green, male catkins are pale yellowish-green
Sun: Full sun to part shade
Water: Medium
Maintenance: Low
Suggested Use: Hedge, Naturalize
Other: Winter Interest
Tolerate: Clay Soil, Wet Soil
Culture
Best grown in evenly moist, well-draining soils in full sun to part shade. Takes well to occasional heavy pruning. Tolerant of poor, wet, and clayey soils. Hardy in Zones 6-10.
Noteworthy Characteristics
Alnus sieboldiana is a large, deciduous shrub or small tree native to foothills, lowlands, and coastal areas of Honshu, the largest of Japan's main islands. Mature plants will reach around 10-30' tall with a multi-stemmed growth habit and spreading to rounded crown. The ovate foliage has doubly serrated margins and will reach 2.5-4.25" long and 1.5-2.25" wide. The minute, apetalous flowers are held in separate male and female catkins. Pendulous, stout, 1.75-3.5" long greenish-yellow male catkins hang from the branches in early spring. Upright, solitary, 1" long, ellipsoid, female catkins emerge in late spring to early summer. They mature from dark red to green and finally form a dark brown, woody, cone-like fruiting structures holding light brown samaras (winged seeds).
Genus name is the Latin name for alder.
The specific epithet sieboldiana honors Philipp Franz von Siebold (1796-1866), German botanist and physician who traveled extensively in Japan.
Problems
Watch for sapsuckers such as aphids and scale. Most alders are susceptible to severe trunk and stem cankers.
Uses
A fast growing windbreak, screen, informal hedge or specimen for parks or large, natural settings. Suitable for coastal gardens and low-lying areas. The persistent, cone-like fruiting structures and greenish-yellow male catkins offer horticultural interest in winter and early spring.