Ironwood | The Morton Arboretum

Ironwood is a tough understory tree with beautiful birch-like leaves, grayish-brown flaky bark, fine-textured drooping branches, and attractive hop-like fruits. Ironwood is considered one of Illinois’ toughest native hardwoods and is not only ornamental but resistant to many disease and insect problems. Excellent tree for naturalized landscapes.

This species is native to the Chicago region according to Swink and Wilhelm’s Plants of the Chicago Region, with updates made according to current research.

Family (English) Birch
Family (botanic) Betulaceae
Planting site City parkway, Residential and parks, Wide median
Tree or plant type Tree
Foliage Deciduous (seasonally loses leaves)
Native locale Chicago area, Illinois, North America
Size range Medium tree (25-40 feet), Large tree (more than 40 feet)
Mature height 25-40 feet
Mature width 15-40 feet
Light exposure Full sun (6 hrs direct light daily), Partial sun / shade (4-6 hrs light daily)
Hardiness zones Zone 3, Zone 4, Zone 5 (Northern Illinois), Zone 6 (City of Chicago), Zone 7, Zone 8, Zone 9
Soil preference Moist, well-drained soil
Tolerances Alkaline soil, Dry sites
Season of interest midsummer, late summer, early fall
Flower color and fragrance Inconspicuous
Shape or form Pyramidal, Round
Growth rate Slow
Transplants well No
Wildlife Browsers, Small mammals, Songbirds
Has cultivars Yes

Native geographic location and habitat:

C-Value: 5. Ironwood is native to Illinois, the Midwest, and the southeastern United States.

Bark color and texture:

The gray-brown bark and trunk are ornamentally attractive, forming long vertical shredding strips.

Leaf or needle arrangement, size, shape, texture, and color:

The alternate, simple, deciduous leaves are 2 to 5 inches long and 1 to 3 inches wide. Medium to dark green leaves with doubly serrate leaf margins and a pointed leaf tip turn yellow in fall.

Flower arrangement, shape, and size:

The male flowers are 1 inch long catkins. Female flowers are small and inconspicuous.

Fruit, cone, nut, and seed descriptions:

The fruit are drooping clusters at the tip of branches that look like hops, hence the common name hop hornbeam. Each small inflated sac has a hard nutlet inside. The fruit changes from creamy green to tan as it ages.

Plant care:

Ironwood prefers full sun to partial shade. It naturally occurs in dry woodland understory areas. It does best in slightly acid soil that is moist, fertile and well-drained, but can tolerate dry, gravelly soils in partial shade, once it is established. It is difficult to transplant and slow to establish. It is not tolerant of salt. Prune it in late winter or early spring.