Homegrown Habitat, October 2024: Hornbeam
Hornbeam displays beautiful foliage in the fall. Photo by Nadiatalent – Own work, Public Domain, commons.wikimedia.org
Hornbeam, with its sinewy, muscled gray bark, is a beautiful tree of the understory that can turn spectacular in fall, its leaves ranging from a clear gold to orange and bright crimson. Sarah Middeleer explains how to grow it and why it’s so important for birds, small mammals, and insects. Write to her at homegrownhabitat@ctaudubon.org.
Hornbeam (Carpinus caroliniana), also known as musclewood, ironwood, and blue beech, is a graceful, slow-growing tree with multiseason interest and suitability for almost any garden. This adaptable small tree is native across a large swath of Canada, the Eastern United States, and as far south as Central America. Its westward reach in the U.S. is to just west of the Mississippi River.
Hornbeam has smooth blue-gray bark that develops a sinewy, muscled appearance. This pattern is repeated in the way the tree grows—in a spiraling, serpentine manner that one author likens to that of bonsai. These qualities contribute to the strong winter interest of hornbeam. The wood is extremely hard, which has limited the tree’s commercial use (Native Americans did use it to make bowls, tool handles, and ox yokes). But the wood’s density helps to protect hornbeam from winter ice damage.
Yet the smooth hornbeam bark is vulnerable to nicks from power equipment. Give your hornbeam (and all trees in your garden) a very generous bed—not only to keep the sharp blades and weed whackers away, but also to permit the beneficial insects that call the tree home a safe place to overwinter in its fallen leaves. Don’t remove the leaves until consistently warm weather occurs in the following spring.
As the tree matures and its canopy spreads, so must the bed. Plant it densely with native ground covers and other herbaceous plants to form a “living mulch.” The Wild Seed Project has clear information on this approach. It is an excellent way to reduce your lawn and to give struggling wildlife a fighting chance in an increasingly forbidding world.
The hornbeam branching pattern is intricate, which creates a fine texture and invites nest builders. This texture is enhanced by the hornbeam leaves, which have pointed tips and finely toothed leaf margins. If the tree is growing in good light conditions, when new spring leaves appear they are wine colored, which contrasts attractively with the bright-green older leaves.
In autumn the foliage color can range from a clear gold to orange and bright crimson. Sometimes the leaves persist all winter, but not as much as on hornbeams from Europe and Asia.
Hornbeam fruits are tiny winged nuts held in small clusters that blend in with the foliage. Photo by Fepup – Own work, Public Domain, commons.wikimedia.org/
Like several other trees in the birch (Betulacea) family, hornbeam produces catkins in early spring as the leaves emerge. Fruits that develop inside the catkins are tiny winged nuts held in small clusters that blend in with the foliage. Many birds, including finches and turkey, favor the hornbeam nutlets. Seed-eating fall migrants, as well as overwintering songbirds, will be glad to find them.
Besides offering excellent cover and shelter, hornbeam hosts over 70 species of moths and butterflies, including the Eastern tiger swallowtail and red-spotted purple butterflies, and the walnut sphinx moth. All of these lepidoptera lay eggs on the tree from which caterpillars emerge.
Another reminder: the ability of a plant to provide plenty of caterpillars makes it invaluable to our songbirds, who rely on thousands of larvae to feed their young each spring. (As entomologist, author, and conservationist Doug Tallamy says, without caterpillars we have no birds.) In addition, the hornbeam seeds, wood, and bark are all food sources for ducks, warblers, rabbits, squirrels, foxes, and beavers.
In the Northeast, hornbeam doesn’t typically grow taller than 15-20 feet, with a similar spread—although in its southern range it can reach greater heights. It may grow as a multi- or single-stemmed tree. In nature hornbeam is typically found in moist woods or along watercourses, but it is adaptable to dryer, sunnier sites. In these days of sometimes brutal summer heat, it would probably be best to site your hornbeam in part shade or full shade in a moist area. Plant in spring only.
Good woody companions for hornbeam in part shade include hop-hornbeam, witch-hazel, serviceberry, redbud, and flowering dogwood, northern arrowwood viburnum, and inkberry. Herbaceous companions (such as those you’d plant in the generous bed around the tree) include cranesbill geranium, sweet Alexanders, may apple, native violets, wild ginger, ferns, and many others.
Hornbeam would make a fine patio tree (although one might lose some of the large bed underneath), where you could easily keep an eye on its watering needs. Also consider it for rain gardens, “ecotones,” (transition zones between a wooded area and lawn or meadow), woodland understory plantings, and other locations. One author recommends it for framing a pathway, due to its attractively arching branches. It doesn’t tolerate salt, so avoid hornbeam as a street tree.
Do you grow hornbeam? Send us a photo if you’d like, especially if it has a bird in the tree. As always, drop us a line at homegrownhabitat@ctaudubon.org
Resources
Books
Anna Fialkoff and Heather McCargo, Native Ground Covers for Northeastern Landscapes, 2022, Wild Seed Project
Heather McCargo and Anna Fialkoff, Native Trees for Northeastern Landscapes, 2021, Wild Seed Project
Mark Richardson and Dan Jaffe, Native Plants for New England Gardens, 2018, Globe Pequot
Edith Roberts and Elsa Rehmann, American Plants for American Gardens, 1929, MacMillan Company, and 1996, University of Georgia
Guy Sternberg with Jim Wilson, Native Trees for North American Landscapes, 2004, Timber Press
Websites
https://extension.psu.edu/underutilized-landscape-plant-carpinus-caroliniana-american-hornbeam
https://plants.ces.ncsu.edu/plants/carpinus-caroliniana/
https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_2/carpinus/caroliniana.htm
