European hornbeam

Identification and origin

Carpinus betulus belongs to the Betulaceae, the birch family, alongside alders and hazels. Its native range runs from Great Britain, France and Spain to southern Scandinavia, central and eastern Europe, the Balkans, Türkiye, the Caucasus and Iran. It has naturalized in Norway and New York State. Its species name means “birch-like.”

It is a medium-sized tree that usually reaches 39.5–59 ft tall, less often 78.5 ft, and 29.5–39.5 ft wide. It takes more than fifty years to reach full size. The crown is pyramidal, oval, rounded or vase-shaped depending on the tree, and the branches tend to droop with age.

• Trunk and bark: smooth and gray, grayish brown on young trees, later splitting into shallow furrows. The trunk shows distinctive fluting, like muscles under the bark.
• Leaves: alternate, simple, oval and dark green, 2–4 in long, with double-toothed margins; the strong parallel veins give them a quilted look. They turn yellow in fall, sometimes orange, and some reddish-brown dry leaves sometimes cling to the twigs until the following spring.
• Twigs: slender and reddish brown, dotted with pale lenticels; the buds, green then light brown, curve slightly against the twig.
• Flowers: catkins, male and female on the same tree, appear in spring before the leaves. Yellowish male catkins are about 2 in long; greenish female catkins about 3 in. They are wind-pollinated.
• Fruit: small, hard brown nutlets, each set on a three-lobed bract. In summer they form drooping clusters about 5 in long and stay on the tree into fall.

The name hornbeam refers to its extremely hard wood. It was once used for ox yokes, chopping blocks, wheels, windmill and watermill cogs, wooden screws and piano hammers, and it also makes excellent firewood. There are many cultivars: ‘Fastigiata’, upright and dense, widely used as a screen; ‘Frans Fontaine’, narrow, for small yards; ‘Pendula’, weeping; ‘Purpurea’, with purplish leaves; ‘Incisa’ and ‘Asplenifolia’, with deeply cut leaves.

Light

Hornbeam grows in full sun or part shade, with two to six hours of direct sun a day. It accepts any exposure, open or sheltered. As a bonsai, it does well in a sunny or lightly shaded spot with good airflow.

Watering

It prefers moist but well-drained soil and handles an occasional dry spell or occasional wet spell. Once well established, it is drought tolerant. In a dry summer, check soil moisture deep around a young tree and water deeply when it is lacking, rather than following a schedule.

In a container, the root ball should never dry out completely: water as soon as the surface of the mix dries, without leaving the pot waterlogged. In winter, simply keep it slightly moist. Avoid very hard, lime-rich water, which eventually yellows the foliage.

Potting mix

Hornbeam adapts to most soils: clay, loam, sand or chalk, acidic, neutral or alkaline. It does best in fertile, moist, well-drained loamy or sandy soil. It handles urban conditions well. In a container, a free-draining bonsai mix is suitable.

Temperature

The tree is hardy in USDA zones 4a to 8b and withstands the harshest continental European climates, below -4 °F. In the ground, its deep roots protect it from frost. In a container, however, the root ball freezes much more easily: protect it during hard freezes. The tree needs its cold winter rest and is not grown indoors.

Repotting

In the ground, it is a large tree that needs plenty of room: allow more than 59 ft of open space. It is planted as a shade tree, as a street tree or as a hedge.

In containers and as bonsai, repot every two years in spring, before the buds open; older trees are repotted less often. The hornbeam bonsai guide covers the mix and root pruning in detail.

Pruning

Grown as a tree, hornbeam needs little pruning. It responds very well to hard pruning, though, which makes it a first-rate hedging plant.

• Tree: prune preferably between late summer and midwinter, so cuts do not bleed heavily. Remove branches that droop too much.
• Hedge: trim once a year, in mid- to late summer. Check first for active bird nests and, if you find one, wait until the young have fledged.
• Cutting back: an overgrown hornbeam hedge can be reduced; it resprouts from old wood.

Propagation

• Seed: the most accessible method, especially for raising young plants to train as bonsai; results are still irregular.
• Cuttings: softwood cuttings; they root with difficulty. Among bonsai growers, hornbeam cuttings and air layers root somewhat better than those of beech.
• Grafting: probably the best method, especially to keep a cultivar true.

Common problems

One symptom can have several causes: yellowing leaves can come from waterlogged soil, water that is too hard, drought or a pest. Look at the tree and its conditions before treating.

• Diseases: no serious diseases are known. Leaf spots appear occasionally; powdery mildew, coral spot and, more rarely, honey fungus can affect it.
• Pests: aphids and caterpillars; on bonsai, mealybugs and scale.
• In containers: root rot from overwatering, and chlorosis from very hard irrigation water.
• Animals: gray squirrels sometimes strip the bark.

Hornbeam is also valuable for wildlife: its fruit feeds small birds and small mammals, its foliage gives them shelter and nesting sites, and it feeds the caterpillars of many moths.

Toxicity

No toxicity has been reported: European hornbeam does not appear among the plants listed as toxic to dogs and cats by veterinary references. Still, keep children and pets from chewing on any part of it.