Alnus x spaethii

The Spaeth alder, also known as Alnus spaethii, is an ornamental hybrid tree much appreciated for the opulence and beauty of its very slender, dark green, shiny, large foliage which remains on the tree for a long time before it falls in winter. The species is of medium size and has a conical, pyramidal, regular habit, wider than the Corsican alder, making it an excellent shade tree. Being very hardy and resistant to pollution, it is found in latitudes as far up as northern Europe, either alone or in rows in urban landscapes. Easy to grow, it tolerates all not too dry soils, in full sun or partial shade.

The Alnus spaethii is a deciduous hybrid tree of the Betulaceae family resulting from breeding in Berlin in 1908 between Alnus subcordata and Alnus japonica. It is a vigorous tree that stands out from other alders by its very large leaves, 18 cm (7.1 in) long and 6 cm (2.4 in) wide, lanceolate in shape, dark green and shiny, with small spaced teeth and curved veins. For this reason it is often confused with other distinct species, particularly with the wild cherry, the persimmon, and the Cornus controversa. In autumn, it displays beautiful autumnal colours in yellow tones. Its dense foliage is carried by loose and upright branches that spread more with age. The tree eventually forms a wide, symmetrical pyramid with a maximum height of 15 metres and a width of 10 metres. It has very fast growth, reaching a rate of 50 cm (19.7 in) per year! The male catkins, yellow-brown in colour and 5.5 cm (2.2 in) long, open in late winter, as early as late January. The female flowers are insignificant. It is an exceptional tree in terms of ease of cultivation. Hardy down to -30°C (-22 °F), it has no specific requirements and can grow in slightly acidic or slightly alkaline soils, even poor ones, as long as they are not too dry.

The Spaeth alder is mainly used alone or in rows in urban public spaces. Thanks to its dense foliage, it is perfectly suited for planting alone to create a shaded corner in a large or medium-sized garden. With its elegant silhouette and reasonable size, this suits more structured gardens, whether old or contemporary. In more natural gardens, plant in a grove with other species of deciduous and evergreen trees with different habits.