1 / 9

Alnus glutinosa

common alder

Betulaceae

Europe, southwest Asia, North Africa

Attracts Pollinators

SunFull Sun – Part Shade

WaterHigh

HardinessZones 3–7

Overview

Alnus glutinosa is a deciduous tree in the birch family, typically growing 40-70 feet (12-21 m) tall with a conical to oval crown, sometimes multi-stemmed. The dark, fissured bark and rounded, obovate leaves 1.5-4 inches (4-10 cm) long, notched at the tip and doubly toothed, are sticky when young, which gives the species its name. It is monoecious, with yellow-brown male catkins 2-4 inches (5-10 cm) long and small reddish female catkins opening in late winter before the leaves. The pollinated female catkins harden into woody, cone-like structures 0.5-1 inch (12-25 mm) long that release winged seed and persist on bare twigs through winter. The roots form nodules with nitrogen-fixing bacteria, letting the tree grow on poor, wet, and disturbed ground while enriching the soil. It grows in saturated soil along streams, ponds, and floodplains and tolerates seasonal flooding that kills most trees. The species is short-lived for a tree, often declining after 60 years, and self-sows freely enough to be invasive in parts of North America.

Native Range

Native to Europe, southwest Asia, and North Africa, from Ireland and Scandinavia south to the Mediterranean and the Atlas Mountains. It grows along rivers, lakeshores, fens, and wet woodland, and has naturalized in parts of North America.

Suggested Uses

Planted along streambanks, pond margins, and wet ground for erosion control and quick screening, spaced 15-25 feet (4.5-7.5 m) apart. Its nitrogen fixation makes it useful in the reclamation of poor or disturbed soils. The catkins feed early pollinators and the seed is taken by finches and other birds.

How to Identify

Recognized by rounded leaves notched at the tip with doubly toothed margins, dark fissured bark, and small woody cone-like fruits that persist on bare twigs through winter. Yellow-brown male catkins and tiny red female catkins appear together in late winter before the foliage. Young shoots and leaves are sticky to the touch.

Appearance

Size & Dimensions

Height40' - 70'

Width/Spread20' - 40'

Reaches mature size in approximately 25 years

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~3 weeks

Winter Spring

Catkins open from February to April, before the leaves, releasing wind-borne pollen. The display is brief, lasting a week or two. Woody fruiting cones develop through summer and shed seed from autumn into the following spring.

Detailed Descriptions

Flower Description

Yellow-brown male catkins, red female catkins

Foliage Description

Dark green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 4-12 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.0 - 7.5(Neutral)

357912

Soil Types

clay loam silt peat

Drainagewet

Water & Climate

Water Needs

High

Frost Tolerance

hardy

Time to Maturity

20-30 years to full size

Care & Maintenance

Care Guide

Grows in full sun to part shade on wet to moist soil and tolerates standing water, heavy clay, and poor fertility better than most trees. Nitrogen-fixing root nodules let it establish on disturbed or nutrient-poor ground without feeding. It is hardy to about -30F (-34C) in zones 3-7 and needs no winter protection. Although it withstands flooding, it grows poorly on dry sites and may suffer in prolonged drought. Trees grow quickly when young, often several feet a year, then slow with age. The roots are vigorous and can lift paving or invade drains near water.

Pruning

Pruning in late summer or autumn avoids the heavy sap bleeding that follows winter cuts. Crossing, dead, or damaged wood can be removed to shape young trees. Coppicing or pollarding is tolerated and produces straight regrowth from the cut stems.