The plant is covered with short, downy hairs. Its taproots are long and strong with many lobed nodules. The plants branch at about 20 inches above the ground when not crowded, but branching is suppressed somewhat in dense stands. Sunn hemp is photoperiod sensitive and flowers in response to shorter days. In Homestead flowering has occurred in 90 days.
Flowers are bright yellow and showy.
Sunn hemp grows to a height of 6 to 7 feet tall in just ten weeks in south Florida. No other cover crop is known to grow so rapidly. In Alabama sunn hemp is planted immediately after corn harvest to prevent erosion of the soil by heavy fall and winter rains. Since this plant is a legume, it can fix much of the nitrogen needed by the next crop. Further sunn hemp can be grown as a high-protein forage for late summer when pastures may perform poorly.