HARDINESS: Zones 3 to 9
PREFERRED SOIL pH: Neutral to slightly acid
PREFERRED SOIL TYPE: Moist to well-drained
PREFERRED LIGHT: Sun to shade
ATTRIBUTES: Deciduous tree with attractive bark; for specimens, foundations
SEASON OF INTEREST: Spring to fall; C. caroliniana blooms in spring, O. virginiana in summer
FAVORITES: C. caroliniana, C. betulus and 'Fastigiata', O. virginiana
QUIRKS: Plants hove very tough wood and are difficult to transplant
GOOD NEIGHBORS: Blends well with many trees and shrubs
WHERE IT GROWS BEST: C. caroliniana in moist soil, O. virginiana in well-drained soil
LONGEVITY: Lives up to 150 years
POTENTIAL PROBLEMS: Gypsy moths
SOURCE: Nursery plants
DIMENSIONS: To 30 ft (9.1 m) tall and wide
Hornbeam in the Landscape
American hornbeam (Carpinus coroliniana) is a sinewy tree also known as iron wood or blue beech. The names refer to its hard wood, bluish gray bark, and resemblance to a beech tree. Its cousin the hop hornbeam (Ostrya virginiana) also has strong wood and the same tough constitution.These trees have a small stature and a neat habit with spreading limbs. These undemanding species grow slowly to 30 ft (9.1 m), and they can be tucked
into a border or foundation grouping without fear that they will outstrip their spaces anytime soon.
The two species may share several characteristics, but there are differences. American hornbeam has smooth bark covering subtle ripples in the trunk, like skin stretched tightly over muscles. Hop hornbeam has the same fluted appearance, but the bark is rough and has a shredded texture. American hornbeam flowers are inconspicuous catkins that appear in spring and are followed by a fall crop of nutlike seeds that birds relish. Hop hornbeam has showy fruit clusters in summer that dangle from branch tips and look like the flowers of hops. American hornbeam turns either yellow-orange or maroon in fall, while hop hornbeam has golden fail color.
Other Care-Free Hornbeams
American hornbeam and hop hornbeam are eastern North American natives with very large natural ranges. European hornbeam (C. betulus) is similar and popular for hedges, because it withstands shearing well. "Fastigiata" is a strongly upright variety that spreads out a bit with age and is often available at nurseries. It grows to 50 ft (15.2m) and makes an excellent landscape tree in Zones 4 to 7.
For best results, select a site that mimics the hornbeams' natural habitats. American hornbeam is a lowland tree happiest in a moist, shady place, while hop hornbeam grows best on higher ground in sun or partial shade. Hornbeams are tough to transplant, so don't plan to move one after it's in the ground. Choose a tree in a large nursery container or a balled tree with a big soil ball. Plant in spring and be careful not to plant too deeply, as burying the lower section of the trunk can lead to problems with disease.
Hornbeams are susceptible to damage by gypsy moth larvae, which eat the leaves in midsummer. However, not every caterpillar is a pest. American hornbeams are important food for the larvae of tiger swallowtail and other butterflies. So you may want to ignore the casual feeding by caterpillars with smooth skins, which are likely to be butterfly larvae, and step in with the biological control Bt (Bacillus thuringiensis), used as directed on the label, if dark, hairy gypsy moth caterpillars feed in large numbers.