Alder Trees: Black vs. Grey Alder Identification & Care

Alders are trees you will find wherever it is wet: along stream banks, in swampy lowlands, and on spring-fed slopes. They are among the first to bloom, often while snow is still on the ground in colder climates, and they drop their leaves while still green in autumn. Two widespread species in cool temperate regions are the black alder and the grey alder, which form significant portions of wetland forests across their native ranges in Europe and parts of Asia. In this part of the tree guide, we cover both alders: what their leaves, flowers, fruits, bark, and buds look like, how they differ, and why they are so useful.

Latin Name	Alnus glutinosa (black alder), Alnus incana (grey alder)
Family	Birch family (Betulaceae)
Group	Deciduous broadleaf trees
Height	Black alder 65–100 ft (20–30 m); grey alder 33–50 ft (10–15 m), sometimes up to 65 ft (20 m)
Lifespan	Black alder 100–120 years, sometimes up to 300; grey alder 50–70 years
Flowering	Early spring, before leaves emerge
Fruits	Small winged nutlets in woody "cones", ripening in autumn
Native Range	Black alder: Europe, Northern Africa, Western Asia; Grey alder: Northern and Central Europe, parts of North America and Asia

How to Identify Alder

Both alders share several common features that distinguish them from many other trees. First, their buds are stalked—each bud sits on a short little stem. Second, small, brown, woody "cones" (the remains of female catkins) hang on the branches all winter long. Third, alders bloom very early on bare branches with long, drooping catkins. In autumn, their leaves fall while still green, without turning yellow.

Leaves

Black alder leaves are 1.5–3.5 inches (4–9 cm) long, almost round or obovate—widest above the middle, with a blunt or even notched, seemingly cut-out tip. The edge is doubly toothed and wavy. Young leaves are sticky and glossy, which is why the black alder's Latin name glutinosa means "sticky." On the underside, there are small tufts of brownish hairs in the vein axils. Grey alder leaves are oval or egg-shaped, 1.5–4 inches (4–10 cm) long, with a pointed tip and serrated edges. The upper side is green, while the underside is greyish or bluish-green and hairy. The leaves are arranged alternately on the twig.

Flowers

Alders are monoecious, wind-pollinated trees. The male catkins are long, drooping, yellowish-pink or brown; they form in autumn and hang at the ends of the branches throughout the winter. The female catkins are short, upright, pinkish, and grow on small stalks. The grey alder is usually the first to bloom—as soon as the average daily temperature rises above freezing. In cool northern climates, it can bloom as early as late winter or March. The black alder typically blooms one to two weeks later. Both bloom for about 10 to 11 days. Alder pollen is one of the earliest causes of spring allergies, while the early flowers and resin are eagerly utilized by bees.

"Cones" and Seeds

Once pollinated, the female catkins become woody and turn into small, 0.6-inch (1.5 cm) brown structures resembling miniature pine cones. In autumn (typically October to November in the Northern Hemisphere), tiny, 0.08–0.15 inches (2–4 mm) long, reddish-brown nutlets with two narrow wings ripen inside them. The cones gradually open and release seeds throughout the winter, while the empty cones remain on the branches until the following year. The wind carries black alder seeds for 200–330 feet (60–100 m), but water is even more important: the seeds contain air pockets, allowing them to float for dozens or even hundreds of miles. This is how black alders establish themselves along rivers. Read more in our tree seed guide.

Bark and Buds

The bark of a young black alder is greenish-brown, smooth, and shiny, but at around 20 to 25 years of age, it begins to crack, darkening to dark brown or almost black, and fissures into small, shallow plates. Grey alder bark is light grey, thin, smooth, and shiny for almost its entire life—this is the easiest way to tell the two alders apart, even from a distance. The buds are stalked, purple or brownish-purple; black alder buds are slightly sticky, while grey alder buds are blunt and covered with 2 to 3 scales.

Black Alder vs. Grey Alder: A Comparison

Feature	Black Alder	Grey Alder
Bark	Dark brown, fissured after 20–25 years	Light grey, smooth, shiny
Leaves	Round, blunt or notched tip, sticky	Oval, pointed, greyish and hairy underneath
Young Shoots	Reddish-brown, sticky	Greyish-brown, hairy, not sticky
Height	65–100 ft (20–30 m)	33–50 ft (10–15 m), sometimes a shrub
Lifespan	100–120 years	50–70 years
Habitat	Wet, swampy areas, riverbanks	Moist areas, clearings, abandoned fields
Flowering	Early to mid-spring	Late winter to early spring

In nature, black and grey alders sometimes cross-pollinate; their hybrids display intermediate characteristics.

Where Alders Grow

Across their native ranges in Europe, Asia, and parts of North America, alders are vital components of riparian and wetland ecosystems. Black alder is widespread across much of Europe and parts of Northern Africa and Western Asia. It thrives in fertile, wet soils with flowing or shallow groundwater—along the banks of rivers, streams, and lakes, on spring-fed slopes, and in peat bogs. Swampy black alder forests are often dense and difficult to navigate: mounds up to 3 feet (1 m) high form around the trunks, with dark water pooling between them. The black alder is a light-loving tree; if shaded out, its seedlings will perish within a few weeks.

Grey alder has a more northern and mountainous distribution, commonly found in cooler climates across Northern and Central Europe, as well as parts of North America and Asia. It quickly colonizes clearings, abandoned fields, and disturbed land, regenerating well from root suckers. In its first years, it grows very rapidly—reaching 13–16 feet (4–5 m) in just five years—but it has a relatively short lifespan of only 50 to 70 years.

Alders Fertilize the Soil

Alders possess a remarkable trait shared by very few other large trees: nodules form on their roots, housing symbiotic bacteria that fix atmospheric nitrogen. Through the alders' fast-decaying fallen leaves, this nitrogen is transferred into the soil, enriching and improving it while increasing humus reserves. Because of this ability, alders are often pioneer species, the first to establish themselves on depleted, abandoned, or disturbed lands, paving the way for other trees to eventually take their place.

Alder Wood

Freshly cut black alder wood is white, but when exposed to air, it quickly takes on a reddish-orange hue. It is soft, lightweight, easy to work with, and exceptionally durable in water—it resists rotting for a long time, which is why it was historically used for well linings, underwater pilings, and water pipes. Today, black alder wood is used for furniture, doors, plywood, and carving, while the sawdust is highly prized for smoking fish and meat. Grey alder wood has similar properties, but because the logs are usually thin, it is rarely milled into lumber. In the past, tannins and dyes were extracted from alder bark, leaves, and cones.

Alders in the Landscape

Black alder is well-suited for wet properties and for stabilizing the banks of ponds and ditches. It tolerates flooding and is resistant to air pollution, though young saplings can be damaged by late spring frosts (they are generally cold-hardy to about −30°F (−34°C), USDA zones 3–7). In parks, ornamental forms of black alder are sometimes grown—featuring leaves that resemble oak leaves or are deeply lobed and feathery, along with a narrow, conical canopy. Grey alder is valued by beekeepers for its early blooming. However, alders should not be planted near the homes of those who suffer from early tree pollen allergies. To learn about other early-blooming spring trees, check out our birch tree guide.