Alnus nepalensis aka Himalayan Alder

Alnus nepalensis, or Nepalese alder, is in the birch family. Its home range spans the Himalayas and south-central China. It also includes northern Indochina. It grows in ravine woods and by streams and rivers. It also grows near villages and on some drier sites. In the Himalayas, it grows at 2,950–8,860 feet [900–2,700 metres].

This fast-growing tree sheds all or some of its leaves. Sources give a range of sizes for garden trees. RHS gives a height above 39 feet [12 metres]. Useful Tropical Plants gives 72 feet [22 metres]. Both sources list trees that reach 98 feet [30 metres]. RHS gives a spread above 26 feet [8 metres]. The trunk is straight, with branches that spread or point up. Green leaves have pale undersides and reach seven inches long. They do not change colour in autumn before they fall.

Long, cream male catkins hang in large groups in autumn. Wind moves pollen from flower to flower. The female parts then form small, woody cones. These stand upright in groups on the bare branches. Catkins and cones add interest when the leaves have gone. RHS lists the tree for bold landscape use and banks. PFAF also lists it for woodland canopy and bog gardens.

Give this alder good light and soil that stays damp. RHS lists full sun or part shade as suitable. It also accepts ground that drains poorly. RHS lists clay and loam, with acid, neutral or alkaline soil. The tree fixes nitrogen, which helps it grow in poor ground. Sources differ on how much cold it can take. Take care when you choose a site. RHS assigns H7, while PFAF gives USDA zones 8–11. Useful Tropical Plants lists warm-temperate and subtropical conditions for growth. It says mature trees can stand some frost. Growers can use seed or hardwood cuttings to raise plants.

People plant Nepalese alder to restore land and shade crops. Its wide roots help hold soil on eroded slopes. The wood serves as poles, fuel and for some building work. Bark yields tannin for dyes and tanning. People have used preparations from it for swollen legs and burns. Such records do not show that home treatments are safe. PFAF lists no known food use or hazard. This does not prove it is safe for people or pets. Watch for alder leaf beetles and alder suckers. Leaf-mining sawflies may also attack the tree. Other threats include Phytophthora root rot and honey fungus.