Carpinus caroliniana: American Hornbeam1
A handsome tree in many locations, the tree slowly reaches a height and spread of 20 to 30 feet. It will grow with an attractive open habit in total shade, but be dense in full sun. The muscle-like bark is smooth, gray, and fluted. Ironwood has a slow growth rate and is reportedly difficult to transplant from a field nursery (although 10-inch-diameter trees were moved with a 90-inch tree spade during the winter in USDA hardiness zone 8b with no problem) but is easy from containers. The fall color is faintly yellow to orange to red and stands out in the landscape or woods in the fall. Brown leaves occasionally hang on the tree into the winter.
Scientific name: Carpinus caroliniana
Pronunciation: kar-PYE-nus kair-oh-lin-ee-AY-nuh
Common name(s): American hornbeam, blue-beech, ironwood
USDA hardiness zones: 3A through 9A (Figure 2)
Origin: native to the majority of the eastern United States, southeast Quebec, and southwest Ontario
UF/IFAS Invasive Assessment Status: native
Uses: sidewalk cutout (tree pit); deck or patio; specimen; street without sidewalk; screen; hedge; tree lawn 3–4 feet wide; tree lawn 4–6 feet wide; tree lawn > 6 ft. wide; Bonsai; shade
Height: 20 to 30 feet
Spread: 20 to 30 feet
Crown uniformity: symmetrical
Crown shape: oval
Crown density: dense
Growth rate: slow
Leaf arrangement: alternate
Leaf type: simple
Leaf margin: double serrate
Leaf shape: ovate, oblong
Leaf venation: pinnate
Leaf type and persistence: deciduous
Leaf blade length: 3 to 5 inches
Leaf color: green on top, paler green underneath
Fall color: yellow, orange, red
Fall characteristic: showy
Flower color: yellow-green
Flower characteristics: not showy; male—hanging catkin; female—spike-like catkin
Flowering: mid to late spring
Fruit shape: elongated, oval
Fruit length: ½ to 1 inch
Fruit covering: dry or hard; ribbed, cone-shaped nutlet
Fruit color: brown
Fruit characteristics: attracts birds; not showy; fruit/leaves not a litter problem
Fruiting: ripens in late summer and early fall
Trunk and Branches
Trunk/branches: branches droop; showy; typically multi-trunked; no thorns
Bark: smooth, bluish gray, thin, with fluted vertical ridges
Pruning requirement: little required
Current year twig color: reddish, brown
Current year twig thickness: thin
Wood specific gravity: unknown
Light requirement: full sun to partial shade
Soil tolerances: clay; sand; loam; acidic; slightly alkaline; well-drained to occasionally wet
Drought tolerance: moderate
Aerosol salt tolerance: none
Roots: not a problem
Winter interest: yes
Outstanding tree: yes
Ozone sensitivity: unknown
Verticillium wilt susceptibility: resistant
Pest resistance: resistant to pests/diseases
Use and Management
With age, a multiple-trunked, low-branching specimen can be very attractive, showing off the bark and trunk form particularly well when lit at night. Tolerant of pruning, the tree can be used as a hedge plant or lends itself well for use as a screen due to the densely foliated crown. It can also be trained for street tree use by pruning to one central leader with small-diameter horizontal branches forming "layers" of foliage in the crown. Some nurseries offer single-stemmed specimens. Well-suited for small spaces in the shade or sun, ironwood is tolerant of occasional flooding. The wood is very hard and strong and makes a great tree for climbing, if allowed to grow with low branches intact. The wood dulls woodworking tools quickly. Nutlets and buds are eaten by many birds and squirrels. If transplanting from the field, do it in the spring.
It performs well even in areas inundated with water for several days to a week or two once it is established. Although moderately drought-tolerant, it is probably best to provide even established trees with some irrigation during dry spells in the South. Ironwood grows in sun or shade (as an understory tree in the woods) and tolerates most soils, including wet, but not alkaline.
Relatively few insects attack hornbeam. Maple phenacoccus forms white cottony masses on the undersides of the leaves.
None are normally very serious. Several fungi cause leaf spots on Carpinus. Leaf spots are not serious, so control measures are usually not needed.
Canker, caused by several fungi, causes infected branches to die back, and entire trees die if the trunk is infected and girdled. Severely infected trees cannot be saved, and infected branches are pruned out. This could limit usefulness in parts of the Deep South.
Koeser, A. K., Hasing, G., Friedman, M. H., and Irving, R. B. 2015. Trees: North & Central Florida. Gainesville: University of Florida Institute of Food and Agricultural Sciences.