Carpinus

American hornbeam occurs naturally over a large area in eastern North America. It thrives in shade and often grows in the forest under a canopy of larger species, on moist lake shores and river banks. It grows as a multi-stemmed shrub or small tree with an attractive crown. The dark grey, smooth and shiny bark emphasises the ridges of the trunk, which look like tensed muscles under the bark.

The leaves have numerous strong parallel veins which give them an attractive wavy shape. In autumn the species has decorative seed catkins resembling paper lanterns, while the leaves take on attractive shades of yellow, orange and red.

American hornbeam is a popular garden tree in North America and is considered hardier than the European hornbeam (C. betulus). In Europe, the American species is grown mainly in special collections. American hornbeam seed was brought to Mustila in 1996 as two separate batches collected in Canada’s Ontario and the United States’ Vermont. Its restrained beauty can be hidden in summer by more luxuriant growth in the Arboretum but its fantastic autumn colours can’t be ignored.

Korean hornbeam is a small extremely beautiful tree with a regular round crown, but it is seldom seen in western gardens. In Finland this East Asian species hardly reaches apple tree dimensions. The leaves are deep green, shiny, with toothed edges, grouped in decorative clusters typical of the hornbeams. They are a bronze colour in spring, while in autumn they turn a blazing orange-yellow, sometimes with interesting, clearly defined splashes of red. The trees are also decorated in autumn by the nutlets in their paper-lantern dangling clusters, typical of the hornbeam genus.

Slow-growing and adapted to dry conditions, the Korean hornbeam is a popular species for bonsai. The tree’s hardiness in Finnish conditions is still a matter for doubt, because it has been so little tested. In Sweden it has shown promise, and at Mustila, too. In its native habitat in the mountain forests of northern China and Korean it has to survive extremely cold winters, but the summer climate there is much warmer than in Finland.

The Japanese hornbeam is perhaps one of the most slender of the genus. Typical of many Japanese trees, it has broad slightly drooping branches. The leaves are long, strongly veined and have toothed edges; the seed catkins are long and drooping. Like the other hornbeams, this species is fairly undemanding about where it grows but is perhaps best under the canopy of larger trees or in occasional shade, like in its native habitat.

The autumn colour is unexceptional and the leaves fall late. In summer the deep green foliage and in autumn the browning seed catkins make it irresistibly attractive. It doesn’t grow very large but its broad, slightly shrubby habit requires plenty of room.

There has been little long-term experience of growing this species in Finland. The trees at Mustila, which can be found among the ashes at the lower end of the Atsalearinne (Azalea Slope), are still young. Seeds of a suitable provenance might well succeed at least in the southernmost parts of the country.