Alnus incana subsp. rugosa
Common Name: hazel alder
Type: Tree
Family: Betulaceae
Native Range: Canada, northeastern United States
Zone: 2 to 6
Height: 15.00 to 25.00 feet
Spread: 15.00 to 25.00 feet
Bloom Time: March
Bloom Description: Purplish-brown (male) and green (female)
Sun: Full sun to part shade
Water: Medium to wet
Maintenance: Low
Flower: Insignificant
Attracts: Birds
Tolerate: Erosion, Wet Soil

Culture

Best grown in medium to wet soils in full sun to part shade. Tolerates mucky soils. Avoid full shade. Winter hardy to UDSA Zones 2-6. Best in cool climates. Does not perform well south of USDA Zone 6.

Noteworthy Characteristics

Alnus incana, commonly called European gray alder, is a large pyramidal tree that grows to 40-60' tall. It is native to Europe and the Caucasus.

Subsp. rugosa, synonymous with and formerly known as Alnus rugosa, is a fast-growing, thicket forming, deciduous, spreading small tree or shrub that is native to wet sandy or gravelly soils, often along the peripheries of lakes, ponds, streams, rivers and swamps, from Hudson Bay to Newfoundland south to Minnesota, Michigan and Virginia. It is most often seen in a multi-trunked form to 15-25' tall with a broad-rounded irregular crown, but infrequently will soar to as much as 50-60' tall. It is commonly called speckled alder because of the white warty lenticils (pores) that speckle the bark. Flowers are monoecious (separate male and female flowers on the same tree), appearing in catkins in March-early April before the leaves emerge. Male catkins (flowers purplish-brown with yellow pollen) are slender, cylindrical and droop to 1 1/2" long. Female catkins (flowers green) are rounded (to 1/2") and clustered on stalks. Female catkins are followed by 1-inch long fruiting cones (strobiles) composed of winged seeds. These fruiting cones mature to reddish-brown in fall with persistence into winter, resemble small pine cones and are attractive to birds. Female flowers are pollinated by wind. Leathery dull green leaves (2-4" long) with wrinkled surfaces and red-hairy undersides are wedge-shaped at the base and pointed at the tip with doubly serrate margins. Insignificant fall color. Root nodules fix nitrogen. Alnus incana subsp. rugosa is very similar in appearance to Alnus serrulata (smooth alder or hazel alder). Rugosa means wrinkled in reference to sunken veins on lower leaf surfaces.

Genus name is the Latin name for alder.

Specific epithet means gray or hoary in reference to leaf color.

Problems

No serious insect or disease problems. Canker can be severe. Powdery mildew and leaf curl may appear. Watch for aphids, leaf miners, tent caterpillars, lace bugs and flea beetles. Chlorosis will occur in high pH soils.

Garden Uses

Best for moist areas of the landscape. Tolerates poor soils. Streambanks. Pond margins.