Mountain Alder, Thinleaf alder
Alnus tenuifolia

Family: Betulaceae

What it is like

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

Alnus tenuifolia is a deciduous Tree growing to 9 m (29ft 6in) at a fast rate. See above for USDA hardiness. It is hardy to UK zone 2. It is in flower in March, and the seeds ripen in October. 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 moist or wet soil.

Height (m): 9

Where it is found

Moist soils by swamps, streams, ponds and lakes in foothills to well up in the mountains.

Western N. America - Alaska to California and New Mexico.

Conservation Status:

Countries/locations it is found in

How it is used

Food

Rating: 1

Catkins - raw or cooked. A bitter taste.

Medicine

Rating: 2

The bark is astringent, emetic, haemostatic, stomachic and tonic. The bark also contains salicin, which probably decomposes into salicylic acid (closely related to aspirin) in the human body. This is used as an anodyne and febrifuge. The outer bark is astringent and is applied as a poultice to bleeding wounds, it also reduces swellings.

Anodyne: Relieves pain, it is milder than an analgesic.

Astringent: Produces contraction in living tissue, reducing the flow of secretions and discharges of blood, mucus, diarrhoea etc.

Emetic: Induces vomiting.

Febrifuge: Reduces fevers.

Haemostatic: Controls internal bleeding.

Stomachic: Aids and improves the action of the stomach.

Tonic: Improves general health. Slower acting than a stimulant, it brings steady improvement.

Other

Rating:

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 tree has an extensive root system and can be planted to control banks from erosion. The bark and the strobils are a source of tannin. A dark dye is obtained from the bark. The colour can range from orange through red to brown. Wood - soft, straight-grained, very durable in water. It is of no commercial value, though it is used locally as a fuel.

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

Soil stabilization: Plants that can be grown in places such as sand dunes in order to prevent erosion by wind, water or other agents.

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.

Nitrogen Fixer: Plants that fix nitrogen in the soil

How it is grown

Landscape Uses: Erosion control. Prefers a heavy soil and a damp situation. Grows well in heavy clay soils. Tolerates very infertile sites. A fast-growing but short-lived tree. There is some confusion over the correct name of this tree with one authority citing the European species A. incana as the correct name. Another report says that this species is closely related to A. incana, but distinct. Some modern works treat it as a subspecies (Alnus incana tenuifolia). 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:Not North American native, Wetlands plant, Inconspicuous flowers or blooms. 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; Secondary; Sunny Edge; Dappled Shade; Bog Garden;

Habit: Tree

Hardiness: 5-7

Growth: Fast

Soil: Medium, heavy (clay)

Shade: Semi-shade, no shade

Moisture: Moist, wet

Things to keep in mind

The freshly harvested inner bark is emetic but is alright once it has been dried.

Its other names

Local names

Synonyms

A. incana tenuifolia. (Nutt.)Breitung.