Introduction

A popular tree of moist to wet soils, common alder is a moderate- to fast-growing (two feet per year) deciduous tree that usually grows to 40 to 50 feet in height with a 20- to 40-foot spread and a 12 to 18-inch trunk but is capable of reaching 80 feet in height in the woods. It is not native but has escaped from cultivation and will form pure stands or thickets in disturbed wet sites. Pyramidal when young, common alder often has multiple stems, making it ideal for use as a screen or specimen, the trees eventually becoming more rounded or oval as they mature. 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 and multi-stemmed growth habit, make common 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): Common alder, black alder, 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: 20 to 40 feet

Crown uniformity: irregular

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: needed for strong structure

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; alkaline; acidic; extended flooding; well-drained

Drought tolerance: moderate

Aerosol salt tolerance: moderate

Other

Roots: not a problem

Winter interest: yes

Outstanding tree: yes

Ozone sensitivity: tolerant

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. It can be pruned to one central leader or used as a multi-stemmed specimen. Branches on central-leadered trees form attractive horizontal layers unlike most other trees. Similar to the dogwoods in this respect. 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. Common 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.

Cultivars include 'Aurea'—golden yellow leaves; 'Fastigiata'—narrow, upright form; 'Laciniata'—leaves not as deeply lobed, vigorous growth; 'Pyramidalis'—upright or columnar form to 50 feet tall, 25 feet wide.

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.