Black alder, Alder - Alnus glutinosa

Black alder, Alder - Alnus glutinosa

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Generalities Black alder, Alder - Alnus glutinosa

There are about 15 species of Alder, widespread in most of the temperate areas north of the equator, and on the mountainous areas of Central and South America. The species A. glutinosa is native to the European continent; it has a light brown, fairly rough bark, and dark green, rounded, medium-sized leaves, usually not reaching dimensions greater than 20-25 meters. The foliage is almost conical in shape, with fairly regular branches and fairly thin branches that are not too vigorous. At the beginning of spring, before the leaves appear, it produces catkins, male and female on the same tree, which in late summer and autumn leave space for fruits, false light green pine cones, which in autumn release numerous seeds. The fruits, once dried, remain on the plant for many months, sometimes for years.

Family and genderFam Betulaceae ... The genus has about thirty species
Type of plantDeciduous trees or bushes
RusticYes for the most common species in Europe
GroundUndemanding. Moist, poor, not calcareous
colorsInflorescences (catkins) brown, woody
HeightFrom 8 to 25 m
PropagationSeed, layering

Alders have been used for centuries to reclaim infertile and water-soaked soils, in fact they preferably grow on stony soils, poor in organic material, even in the presence of stagnant water. It is not recommended to bury an alder in acid soils or in areas very subject to long periods of drought.Furthermore, these plants, as well as legumes, have shown to be in symbiosis with nitrogen-fixing bacteria, which makes them also useful for improving the chemical composition of the soils in which they are planted.Multiplication

it happens by seed, in spring, using the seeds of the previous year, to which it is appropriate to spend at least a few months in a cold place, to simulate the winter season. In spring you can also practice cuttings, which must be rooted in a mixture of soil and sand in equal parts, which must always be kept moist until the rooting of the cuttings is complete.

Pests and diseases

this plant does not particularly fear pests and diseases; occasionally the sprouts can be ruined by aphids, in addition pay attention to rameal cancers and fungal diseases.


A. incana, gray alder, native to central Europe, has smooth and gray bark.
A. cordata, an Italian alder, originally from Italy and Corsica, needs a lot of light.
A. rubra, red alder, native to the American continent.


They are present in Europe, North Asia and North America. They are very frequent in wet and marshy areas or are periodically flooded. The diffusion of varieties depends on the climate and also on the altitude. In the past they have been used for the reclamation of ponds and authentic woods have been created with one or more varieties of these plants.


The ideal climate is that of the cool pre-Alpine areas. They absolutely don't like torrid areas. Only the white alder is able to adapt to living in those conditions.


To get small plants you can follow different roads.
First of all, you can try sowing. An important trick is to have the seed vernalize. It must be kept outdoors during the winter or in the fridge for several months, at low temperatures. This helps the germination reproducing the natural conditions.
Sowing takes place in spring in a mixture of sand and peat, even without covering the seed. The soil must always be kept moist, without stagnation. The plants should be born within two weeks. A faster method for obtaining an adult plant is the layering of ceppaia. The mother plant must be cut at the collar. It will then be stimulated to produce new shoots from the base. These must be partially covered with earth. As a result they will produce roots and can be detached and planted individually.
It should also be noted that it is a native plant in Italy. Anyone wishing to plant it in their own land can try to ask for copies from the State Forestry Corps.

Black alder (Alnus glutinosa)

It has 10 cm long and 7.5 cm long leaves, dark green. Above are smooth, but below are hairy. The young leaves and twigs are sticky. The bark is gray and cracked. The catkins are 10 cm long, yellow-green. The female ones instead are red. It has woody fruits, dark and 2 cm long. The crown is a wide cone (but often grows like a bush and therefore has more trunks) and can reach 25 m in height. It is native to North Africa, East Asia and Europe. It lives in river areas where woods are created with pure essence or in combination with other trees. It lives up to an altitude of 1200 meters.
The "imperialis" variety has feathery, delicate and very elegant foliage.

White alder (alnus incana)

He is a native of the Caucasus and of Europe. Its range extends up to an altitude of 1500 meters. It is widespread in the Alps and the Apennines, as it lives in a typically mountainous environment, near courses or stretches of water.
It has ovate leaves, 10 cm long and 5 wide, dark green above and gray and hairy below. The bark is dark gray. The male pendulous catkins are 10 cm long, on the red. The fruits are conical and about 2 cm long.
The crown is broad cone, the trunk is straight and thin and reaches a height of 20 m.
The golden variety bears golden leaves and catkins while the branches are orange.
It is also often used for the consolidation of embankments and embankments.

Neapolitan alder (alnus cordata)

It has round leaves, long and 10 cm wide. The color is dark green on the upper side and pale and hairy on the lower one. The bark is gray, slightly cracked and smooth.
The female catkins are small and red, the male ones about 8 cm long, the woody fruits and 3 cm long.
The crown has a broad cone shape, shiny green and very dense. The height goes from 15 to 25 m. It is native to our country and can also be found in Sardinia. It can create forests along the banks of rivers.
It produces a light wood.

Red alder

It has ovate leaves, more than 10 cm long and 8 wide, with a pointed apex. Above are dark green while below are blue-green. The contrasting rib is reddish instead. The bark is grayish. The male catkins are 15 cm long, yellow. Females are red.
The crown is wide and can reach 15 meters in height.
It looks very similar to a birch.
It is native to North America, especially in the north-west. It lives on the banks of rivers.

Black alderWhite alderNeapolitan alderRed alder
Height25 m20 m25 m15 m
Lifespan150 years100 years100 years100 years
leavesobovateovateroundFrom ovate to elliptical
FormA wide cone or bushWide coneWide coneWide cone
BarkDark gray, crackedDark gray, crackedGray and smooth, slightly crackedPale gray, wrinkled
HabitatRiver up to 1200 mMountainous, wetlands up to 1500 mMountainous, wetlands up to 1500 mOn river banks and along the coasts. Also mountainous areas

Other varieties

Alnus viridis: in America, Asia and Europe
Alnus acuminata: Americas
Alnus orientalis: Turkey, Syria, Cyprus
Alnus Tenuifolia: North America
Alnus rugosa: North America

The alder and the nitrogen fixation

Alders are typical "pioneer" plants: they adapt to living in poor and ecologically disadvantaged soils. It is therefore always used for the reclamation of marshlands or for the consolidation of embankments and embankments.
Rhizobium (nitrogen-fixing) bacteria nestle in their roots and cause the emergence of radical nodules. The bacterium removes nutrients from the plant, but returns others, including nitrogen (which the bacterium derives from the air).
In this way the plant is able to make the soil more fertile. It has also been shown that when an alder specimen dies, with its decomposition, it enriches the soil in nitrogen much more than other plants.
It is so useful to the environment at all times: when it is alive and when it is no longer alive.

Alder and mushrooms

The alder feeds numerous mushrooms when it perishes and becomes dead wood. He may also establish a symbiotic relationship with some of them. In general it was found that more than 24 species are usually found in the vicinity of these trees. They are therefore very precious plants.
On the other hand, the presence of a certain type of fungus can help in identifying pathologies of that particular group of trees.

Legends and traditions

In mythology this tree was associated with the god Chronos and the dead.
In the Middle Ages it was associated with witchcraft because of its blood-red wood and its strange habit of living near or in water. In some areas, however, it was also attributed the ability to keep the fire away from the houses.
In the south of France there are several festivals that consecrate this tree as a symbol of the arrival of spring.

Black alder, Alder - Alnus glutinosa: Uses of alder wood

Its appearance is particularly pleasant: it is a red-orange color, very smooth and free of knots and imperfections. The wood of black alder It is renowned for its durability in a humid environment. For this reason it was used for the construction of piles. In particular, all the base of Venice was and still is built with this wood. At the time, black alders from present-day Croatia were used.
His wood is also used in violin making, especially for the production of high-end guitars. It is also useful for making all those wooden items that need to come into contact with water: tubs, tubs, saunas, parquet to use in kitchens or bathrooms and as decoration in aquariums. The red alder was used by the American Indians for the construction of canoes.
It also provides excellent firewood: it has a very high calorific value. It is in great demand by bakers and as a fuel for those who produce distillates. Its wood is, as we have said, very smooth and homogeneous. It is therefore ideal for sculpture. They make ornaments for furniture, models and toys. It was also the tree of choice for the production of clogs (in fact it is to this tree that Ermanno Olmi refers to in the "tree of the hooves")
Its wood and its bark contain a lot of tannin. The latter was used for the flavoring of some bitters and to obtain a gray dye.
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  • White alder

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  • Neapolitan alder

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