This perennial member of the pea family (Fabaceae) is native to the area between Ontario eastward to Maine and southward to Georgia including Tennessee. It is found in Hardiness Zones from 4 through 9, thus, Chattanooga is a perfect area for the American senna.
This species produces large plants up to 6 feet tall that flower in July and August. The bright yellow flowers attract bees, butterflies and other pollinators. During autumn, the leaves undergo a remarkable color change again, adding accents to the garden. While this plant is perennial it also is deciduous.
American senna prefers moist to medium moist loamy soils along with full sun to partial shade. It is often found in moist woods and disturbed areas such as road ditches and bridge embankments.
This plant is often used as a living hedge, effectively blocking access past it.
It is used as a cover crop and food source for quail and other hunted bird species.
While the light-yellow flowers of this plant are beautiful, the flowers, seeds and leaves have a toxin called anthraquinones and can cause a fatal situation, especially in children. This toxicity can be greater or lesser depending on a person’s age, weight, individual medical condition, and exposure. Children can be particularly susceptible.
This species has few diseases or insect pests that the home gardener needs to be aware of.
Due to the large tap root of this plant, dividing the roots in an effort to propagate it is often not possible. Instead, the gardener can collect the seed heads in late autumn and sow them in the early spring.
According to iNaturalist, this species is currently found at Reflection Riding Arboretum and Nature Center.
In the northeast US this plant is state-designated as “endangered,” specifically in Pennsylvania, Massachusetts, Connecticut, Rhode Island, and Vermont. Here in Tennessee it is considered “secure,” with no restrictions on its distribution or care.
About the Author
Charlie Belin is a retired professor and biological oceanographer. He taught five courses in the University of Georgia system for many years from his home base in Savannah, Georgia.
Charlie loves hiking at Reflection Riding, teaching children about the ecology of the area, and interacting with the Reflection Riding staff. They are GREAT!