Alnus incana aka Grey Alder

Alnus incana, or grey alder, belongs to the birch family. It grows as a native tree in Europe and the Caucasus. Plants For A Future also lists temperate Asia and North America. It is not native to Britain or Ireland. This tree sheds its leaves and has an upright, cone-shaped crown. The RHS gives a height of about 66 feet [20 metres]. Its crown can spread beyond 26 feet [8 metres]. It can take 20–50 years to reach its full size.

The leaves are dark green and reach about four inches long. Grey-white hairs cover the lower side of each leaf. Male flowers grow in hanging clusters called catkins. These are yellow-brown and hang in groups of three or four. They appear in late winter or early spring, before leaves open. The tree forms oval fruit in summer. Its leaves can shelter other trees that grow in woods. Fallen leaves help improve poor sites for plant growth. Root bacteria that fix nitrogen also help improve these sites.

Grow grey alder in full sun or part shade. It prefers moist soil that drains well and is moderately fertile. It also grows in poor, wet ground and tolerates dry soil. The RHS lists clay, loam, sand and chalk as suitable. It grows in acid, neutral and alkaline soils. Both open and sheltered sites suit it. Its H7 rating means it withstands very cold European climates. Gardeners can grow it from seed or hardwood cuttings. The RHS says to prune between leaf fall and midwinter.

Grey alder suits gardens for wildlife and those with informal planting. It also suits coastal planting and woodland gardens as a canopy tree. Plants For A Future also lists bog gardens as suitable sites. It grows fast and helps shelter trees planted for long-term woodland cover. Root bacteria take nitrogen from the air. Nearby plants can use some of that nitrogen. It tolerates polluted soil, so it can help reclaim land. Pests may include alder sucker and alder leaf beetle. Leaf-mining sawflies may also attack it, as may Phytophthora and honey fungus.

Its food value is low, though some parts are edible. The inner bark has bitter tannins and needs a great deal of processing. Even then, it offers little food value and stays bitter. You can boil and eat male catkins. They taste bitter and resinous, with a taste of resin. Plants For A Future reports no known hazards or medicinal uses. That report does not establish safety for every person or pet.