Grey Alder, Speckled alder, Thinleaf alder, White Alder
Alnus incana

Family: Betulaceae

What it is like

Bloom Color: Purple, Red. Main Bloom Time: Early spring, Late spring, Mid spring. Form: Pyramidal.

Alnus incana is a deciduous Tree growing to 18 m (59ft) by 5 m (16ft) at a fast rate. See above for USDA hardiness. It is hardy to UK zone 2. It is in flower from February to March. The species is monoecious (individual flowers are either male or female, but both sexes can be found on the same plant) and is pollinated by Wind. It can fix Nitrogen. Suitable for: medium (loamy) and heavy (clay) soils and can grow in heavy clay and nutritionally poor soils. Suitable pH: mildly acid, neutral and basic (mildly alkaline) soils. It can grow in semi-shade (light woodland) or no shade. It prefers dry moist or wet soil. The plant can tolerate maritime exposure.

Height (m): 18

Where it is found

Mountains, especially on poor soil.

Europe. Introduced in Britain.

Conservation Status:

Countries/locations it is found in

How it is used

Food

Rating: 0

Medicine

Rating: 0

Other

Rating: 3

This species fixes atmospheric nitrogen and is also tolerant of polluted soils, it can be used for land reclamation, especially on coal tips. This is an excellent pioneer species for re-establishing woodlands on disused farmland, difficult sites etc. Its fast rate of growth means that it quickly provides sheltered conditions to allow more permanent woodland trees to become established. In addition, bacteria on the roots fix atmospheric nitrogen - whilst this enables the tree to grow well in quite poor soils it also makes some of this nitrogen available to other plants growing nearby. Alder trees also have a heavy leaf canopy and when the leaves fall in the autumn they help to build up the humus content of the soil. Alder seedlings do not compete well in shady woodland conditions and so this species gradually dies out as the other trees become established. The bark and the fruits contain up to 20% tannin. Wood - light, soft, fairly elastic, easy to split. Used for clogs, bowls, woodcuts etc. Much valued by cabinet makers.

Pioneer: Plants, usually trees and shrubs, that can be used to reforest land.

Soil reclamation: Plants that can be grown in such circumstances an the spoil tips of mines in order to restore fertility.

Tannin: An astringent substance obtaied from plants, it is used medicinally, as a dye and mordant, stabilizer in pesticide etc.

Wood: A list of the trees and shrubs that are noted for having useful wood.

Food Forest: Plants for Edible Forest Gardens and Food Forests.

Nitrogen Fixer: Plants that fix nitrogen in the soil

How it is grown

Landscape Uses:Pollard, Specimen. Prefers a heavy soil and a damp situation. Grows well in heavy clay soils. Thrives in drier soils than many other members of this genus. Tolerates very infertile sites. This species has a symbiotic relationship with certain soil micro-organisms, these form nodules on the roots of the plants and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby. Special Features:Attractive foliage, Not North American native, Wetlands plant, Inconspicuous flowers or blooms. The plant is heat tolerant in zones 6 through 1. (Plant Hardiness Zones show how well plants withstand cold winter temperatures. Plant Heat Zones show when plants would start suffering from the heat. The Plant Heat Zone map is based on the number of "heat days" experienced in a given area where the temperature climbs to over 86 degrees F (30°C). At this temperature, many plants begin to suffer physiological damage. Heat Zones range from 1 (no heat days) to 12 (210 or more heat days). For example Heat Zone. 11-1 indicates that the plant is heat tolerant in zones 11 through 1.) For polyculture design as well as the above-ground architecture (form - tree, shrub etc. and size shown above) information on the habit and root pattern is also useful and given here if available. The plant growth habit is a standard with a non-suckering single trunk. In garden design, as well as the above-ground architecture of a plant, root structure considerations help in choosing plants that work together for their optimal soil requirements including nutrients and water. The root pattern is branching: a heart root, dividing from the crown into several primary roots going down and out .

Propagating it: Seed - best sown in a cold frame as soon as it is ripe and only just covered. Spring sown seed should also germinate successfully so long as it is not covered. The seed should germinate in the spring as the weather warms up. When large enough to handle, prick the seedlings out into individual pots. If growth is sufficient, it is possible to plant them out into their permanent positions in the summer, otherwise keep them in pots outdoors and plant them out in the spring. If you have sufficient quantity of seed, it can be sown thinly in an outdoor seed bed in the spring. The seedlings can either be planted out into their permanent positions in the autumn/winter, or they can be allowed to grow on in the seed bed for a further season before planting them. Cuttings of mature wood, taken as soon as the leaves fall in autumn, outdoors in sandy soil.

Best place to grow: Woodland Garden Canopy; Bog Garden;

Habit: Tree

Hardiness: 2-6

Growth: Fast

Soil: Medium, heavy (clay)

Shade: Semi-shade, no shade

Moisture: Dry, moist, wet

Things to keep in mind

Its other names

Local names

Synonyms

Betula alnus incana.