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  • Writer's pictureJennifer Anderson

Understory: Ironwood vs. Ironwood

Ostrya virginiana fruits resemble hops
Hophornbeam photo by Salomé Bielsa

Carpinus caroliniana male flowers
Hornbeam photo by Katja Schulz












Here’s a tripper-upper: Hornbeam and Hophornbeam, two understory trees that also both go by the name Ironwood.


Wait, there’s more: Both are in the birch family, both naturally grow in the understory, both have a similar, rounded form, and both are wind pollinated. It took me a while to figure out the differences and why I would plant one vs. the other.


Knowing your conditions helps: Hornbeam, Carpinus caroliniana, likes moist soil and full sun to full shade; and Hophornbeam, Ostrya virginiana, prefers medium to dry soil and sun to light shade.


Carpinus caroliniana, Hornbeam
Hornbeam fluted trunk by Tom Potterfield

Here’s a closer look.

Another name for Hornbeam is Musclewood because of its smooth outer bark covering bumps that give it a slight appearance of straining to hold itself up.


It has a short, stout trunk with low branches that flare out underneath a wide crown.


In the wild it’s most common in the floodplain under the shade of taller trees and where it tolerates occasional flooding.


Carpinus caroliniana fall foliage
Fall foliage on Hornbeam

Spring catkins can be showy in summer as they change from light green to tan and persist into winter. Hornbeam's fall foliage features yellows, oranges and sometimes blazing reds compared with plain yellow on Hophornbeam.


Papilio glaucus Eastern Tiger Swallowtail
Eastern Tiger Swallowtail

Hornbeam is fast growing and supports dozens of caterpillars including the Eastern Tiger Swallowtail, Papilio glaucus. Birds like Hornbeam for cover and nesting, and ducks and small mammals eat the seeds.



Ostrya virginiana Hop Hornbeam
Hophornbeam's shaggy trunk

The trunk may be the most differentiating feature between these trees as Hophornbeam’s bark is gray, slightly reddish, and shaggy, great for songbirds pecking around for invertebrates.


Hophornbeam also climbs higher in nature than Hornbeam, preferring the dry shade up in the hills. In cultivation, it does well in medium to dry areas, and in a sunny spot it likely will grow taller and faster.


Like Hornbeam, Hophornbeam forms a beautiful canopy with rich, green leaves. Its female catkins swell into papery pods that resemble hops strung together along the branches. Inside each sac is a ¼-inch nutlet favored by birds, turkey, pheasant and small mammals.


Hophornbeam may get slightly taller than Hornbeam, up to 40 feet, and its trunk, usually in the 10-inch range, can widen to 2 feet across.


Red-spotted Purple Butterfly
Red-spotted Purple

Great as a shade tree or part of a butterfly garden, Hophornbeam serves as a host for caterpillars of the Red-spotted Purple and Eastern Tiger Swallowtail butterflies, as well as those of several moth species.


Fun fact: Back in the day, Hophornbeam was used to make airplane propellers and sleigh runners.


Sources



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