A common shrub of wetlands throughout Indiana, buttonbush (Cephalanthus occidentalis) attracts numerous butterflies with its beautiful white flowers that open in early to mid-summer. A member of the madder family (Rubiaciae), it occupies a unique niche where few other woody plants grow. Only bald cypress, which are confined to the southwest toe of Indiana as a native plant, are more tolerant of growing in ponded water than buttonbush.
Buttonbush is a medium to large shrub, sometimes reaching 10 to 12 feet in height. The leaves are simple and typically opposite or occasionally in whorls of three on vigorous shoots. They are usually 4 to 6 inches long with untoothed margins. Buttonbush is one of our latest woody plants to leaf out, typically remaining bare until mid-May. This usually saves their very frost-sensitive foliage from damage during spring cold spells.
The flowers typically develop in late June and continue through July. The white spherical flowerheads are 1 to 1.5 inches in diameter and are composed of numerous individual flowers tightly packed together. The fragrant flowers attract numerous pollinators for nectar and pollen. Many conspicuous butterfly species visit them including tiger swallowtail, buckeye, painted lady, pearl crescent, red admiral, silver-spotted skipper, monarch and viceroy. Bees, including honeybees, bumblebees, cuckoo bees, leaf-cutting bees and green metallic bees, also visit the inflorescences. Following pollination, the white flower parts drop, leaving a red seedhead that turns brown when mature. The seeds are popular with birds, especially ducks that frequent the wetland habitat of buttonbush.
Buttonbush is most frequently found in two types of wetlands in central Indiana. Their most common habitat is flatwoods depressions, which are low areas in flat upland woods where water ponds in the spring. Here they grow with wet-tolerant trees such as swamp white oak, pin oak and red maple. Winterberry (Ilex verticillata) and swamp rose (Rosa palustris) are other shrubs that share this habitat. These wetlands typically dry out late in the season. In the areas of deepest ponding in the center of these depressions, buttonbush frequently grows without associates due to its exceptional tolerance of standing water.
The other frequent habitat in central Indiana are overflow channels and old sloughs in floodplains which also generally hold water in the spring. Sycamore and silver maple are the most frequent trees found with buttonbush in this habitat.
Fortunately, buttonbush does not require standing water for successful cultivation in the landscape. It will grow fine in moist garden soil. It does well in full sun or filtered shade. It is widely available from nurseries that specialize in native shrubs. It may also be easily grown from seed collected in the fall. Keep the seeds refrigerated during the winter and spread them across a germination tray in the spring, where they will readily germinate in warm weather.