Christmas senna is an open, sprawling, evergreen shrub that gets up to 12 ft (3.7 m) tall with about the same spread. The leaves are pinnately compound with 3-5 pairs of oval leaflets, increasing in size toward the tip, and averaging about 1.5 in (3.8 cm) in length. Christmas senna blooms in late summer and fall (and through the winter if there's no frost) with bright yellow flowers, about 1/2 in (1.3 cm) wide in long-stalked racemes (spike-like clusters) consisting of 3-12 blossoms. The mature pods are brown, cylindrical, partially segmented and 3-6 in (7.6-15.2 cm) long.
Christmas senna is native to South America. It has escaped cultivation and become established in disturbed areas in central and southern Florida and in the Bahamas.
Easy to grow and fast-growing. Moderately salt tolerant. Likes sandy soil. Light: Full sun for best flowering. Will tolerate partial shade. Moisture: Prefers moist soil, but not waterlogged. Only moderately drought tolerant. Hardiness: USDA Zones 9 - 11. Frost kills Christmas senna to the ground, but it resprouts in spring so it also succeeds in Zone 8 as a perennial. Propagation: By seeds.
In this photo Christmas senna is seen naturalizing a disturbed road shoulder in Central Florida.
Christmas senna is recommended for butterfly gardens in central and southern Florida, the Gulf Coast of Alabama, Mississippi, Louisiana and Texas, and most of California. The flowers are very showy. In South Florida Christmas senna is planted in roadway median strips and around parking lots. It does well near the coast. Christmas senna needs frequent pruning to control sprawl and to develop a strong branch system that won't break under its own weight. Larger specimens may require staking to keep them from falling over. Frequent pinching of young shoots during the growing season will encourage branching and increase the number of flowers.
The caterpillars of the sulphur butterflies (family Pieridae) feed on this and other species of Senna and Cassia. Adult sulphurs are especially fond of Christmas senna. See Floridata's profiles of the sleepy orange and the cloudless sulfur.
Christmas senna is listed by the Florida Exotic Pest Plant Council as a Category I species that is invading and disrupting natural communities in central and southern Florida. However most observers note that it invades areas that already are disturbed (canal banks, cleared lots, etc.) as opposed to undisturbed natural areas. Other non-governmental organizations still recommend Christmas senna for butterfly gardens, and its cultivation is not prohibited.