Ostrya spp.

Hop-hornbeam

Betulaceae Temperate Northern Hemisphere

SunFull Sun – Part Shade

HardinessZones 4–8

Overview

Ostrya is a genus of small to medium deciduous trees in the family Betulaceae, the hop-hornbeams, with about eight species across the temperate Northern Hemisphere. Familiar species include the American hop-hornbeam (O. virginiana) of eastern North America and the European hop-hornbeam (O. carpinifolia) of southern Europe and western Asia. Trees reach 8-18 m (26-59 ft) tall, with a rounded crown, finely shreddy grey-brown bark, and slender, often slightly drooping branches. The alternate leaves are oval with doubly toothed margins and parallel veins, 5-12 cm (2-5 in) long, turning yellow in autumn. Trees are wind-pollinated and monoecious: male catkins form in autumn and open with the leaves in spring, while female flowers develop into hanging clusters of papery, inflated bladder-like sacs, each enclosing a small nutlet, that resemble the fruits of hops and give the genus its common name. The wood is very hard and heavy, sinking in water, which has earned these trees the additional name ironwood. The genus grows as an understorey or edge tree in well-drained woodland, often on slopes and ridges.

Native Range

Ostrya is native to the temperate Northern Hemisphere, with species in eastern North America, Central America, southern Europe, and temperate Asia. The trees grow in well-drained woodland, on slopes, ridges, and rocky hillsides, usually as understorey or forest-edge trees.

Suggested Uses

Ostrya species are grown as small shade, street, and specimen trees where a compact, slow-growing hardwood suits the site, and in woodland and naturalistic plantings. The very hard wood has been used for tool handles, fence posts, and turnery.

How to Identify

A small to medium deciduous tree 8-18 m (26-59 ft) tall with finely shreddy grey-brown bark and oval, doubly toothed leaves with parallel veins. The hanging clusters of papery, inflated, bladder-like sacs that enclose the nutlets and resemble hop fruits are the clearest feature, along with the very hard, heavy wood.

Appearance

Size & Dimensions

Height26' - 59'

Width/Spread20' - 39'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

Spring

Flowering is in spring, around April to May, as the leaves expand. The drooping yellowish male catkins shed pollen on the wind, and pollinated female flowers develop over summer into hop-like clusters of papery sacs that ripen and shed their nutlets in autumn.

Detailed Descriptions

Foliage Description

green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 7.5(Neutral)

357912

Soil Types

loam rocky clay

Drainagewell drained

Water & Climate

Water Needs

Low

Frost Tolerance

hardy

Time to Maturity

slow; many years to mature size

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Ostrya grows in full sun to partial shade in moderately fertile, free-draining soil and tolerates a range of pH from acidic to alkaline, about 5.5-7.5. The trees are drought-tolerant once established and grow slowly into long-lived specimens. They are hardy through roughly USDA zones 4 to 8 depending on species. Deep, well-drained ground suits them, while wet or compacted soils are tolerated poorly. Few serious pests or diseases affect them, though the slow growth means damage is replaced gradually.

Pruning

Pruning is done in late winter to remove dead, crossing, or low branches and to shape young trees, since the dense wood heals slowly. Mature hop-hornbeams need little pruning and keep a naturally rounded crown.