Introduction

A popular tree of moist to wet soils, common alder is a moderate- to fast-growing (two feet per year) deciduous tree. This upright, columnar cultivar to 20-foot spread and a 12- to 18-inch trunk but is capable of growing taller. The species is not native but has escaped from cultivation and will form pure stands or thickets in disturbed wet sites. The two- to four-inch-wide, dark green, roundish leaves with toothed edges and pale undersides are joined in spring by rather insignificant male and female flowers. Foliage remains green well into the fall. It is the fruits that are most interesting—small, nutlike, one-inch "cones" that persist throughout the fall and winter, long after the darkening leaves have fallen. These fruits, along with the attractive, dark brown, furrowed bark, make alder an attractive landscape specimen throughout the winter. The fruits are food for a variety of wildlife.

General Information

Scientific name: Alnus glutinosa

Pronunciation: AL-nus gloo-tih-N0-suh

Common name(s): 'Pyramidalis' common alder, `Pyramidalis' black alder, `Pyramidalis' european alder

Family: Betulaceae

USDA hardiness zones: 3A through 7B (Fig. 2)

Origin: not native to North America

Invasive potential: invasive non-native

Uses: screen; specimen; reclamation; shade

Availability: not native to North America

Description

Height: 40 to 50 feet

Spread: 15 to 20 feet

Crown uniformity: symmetrical

Crown shape: pyramidal, oval

Crown density: dense

Growth rate: moderate

Texture: coarse

Foliage

Leaf arrangement: alternate (Fig. 3)

Leaf type: simple

Leaf margin: double serrate, serrate

Leaf shape: orbiculate

Leaf venation: pinnate

Leaf type and persistence: deciduous

Leaf blade length: 2 to 4 inches

Leaf color: green

Fall color: no color change

Fall characteristic: not showy

Flower

Flower color: red, purple

Flower characteristics: not showy

Fruit

Fruit shape: oval, elongated

Fruit length: less than .5 inch

Fruit covering: dry or hard

Fruit color: brown

Fruit characteristics: does not attract wildlife; showy; fruit/leaves not a litter problem

Trunk and Branches

Trunk/bark/branches: branches don't droop; showy; typically one trunk; thorns

Pruning requirement: little required

Breakage: resistant

Current year twig color: gray, brown

Current year twig thickness: thin, medium

Wood specific gravity: unknown

Culture

Light requirement: full sun, partial sun or partial shade

Soil tolerances: clay; sand; loam; acidic; alkaline; well-drained; extended flooding

Drought tolerance: moderate

Aerosol salt tolerance: moderate

Other

Roots: not a problem

Winter interest: yes

Outstanding tree: yes

Ozone sensitivity: unknown

Verticillium wilt susceptibility: resistant

Pest resistance: resistant to pests/diseases

Use and Management

A good plant for establishing along stream banks to stabilize soil and add interest, alder can also be used as a specimen in a more formal landscape where wet soil challenges most other plants. The columnar growth habit makes it suited for a screen planted on 10-foot centers, and for areas with narrow overhead space. Some horticulturists believe that it could be used as a substitute for Lombardy poplar. It requires little pruning to develop into a well-formed tree. Unfortunately, it is usually not grown in nurseries, but nursery operators should be encouraged to grow this adaptable tree.

Common alder will grow easily in full sun or partial shade in almost any landscape setting since the trees are able to "fix" nitrogen, or take it out of the soil atmosphere, enabling these trees to grow in the poorest and wettest soils where other trees might fail. Alder will grow best in wet or moist soils, acid or alkaline, and have even been observed growing with roots submerged in water, but it is also tolerant of moderate drought, compaction, and urban stress. Common alder transplants easily and will seed itself into an area, creating a thicket if it is planted and left alone in an area that is not maintained. It remains to be seen whether this cultivar will do the same.

Other cultivars include 'Aurea'—golden yellow leaves; 'Laciniata'—leaves not as deeply lobed, vigorous growth.

Propagation is by seed. Cultivars are grafted onto seedling root stock.

Pests

Leaf miners, tent caterpillars. Tent caterpillars can cause significant defoliation, but trees normally recover.

Diseases

Powdery mildew and cankers, but these are usually not serious.