Cassia can be a delight in the fall landscape because it is covered with cheerful yellow flowers when few other plants are blooming. Plus, cassia provides interesting foliage during other times of the year.
Another benefit of cassia plants is that they serve as larval host plants for three types of Florida butterflies—cloudless sulphur, sleepy orange, and orange-barred sulphur.
Two forms of cassia are most popular in Florida gardens—candlestick bush (Senna alata), and butterfly bush or Christmas senna (Senna bicapsularis).
The terms "cassia" and "senna" are used somewhat interchangeably, since these plants were once classified under the genus Cassia.
Planting and Care
Both candlestick bush and Christmas senna grow best in Zones 9–11. In North Florida the plants will freeze back but should return in the spring unless winter was especially harsh. Remove any cold-damaged branches after the last frost date and wait for new shoots to emerge.
Candlestick bush can reach 5 to 8 feet tall and 3 to 4 feet across. Christmas senna can reach a height of 12 feet, though it often sprawls if not staked upright.
Both plants are tolerant of many soil conditions and do best in full sun with moderate water until they are established.
Gardeners who wish to grow Senna bicapsularis should be aware that it resembles Senna pendula var. glabrata, a plant that has been identified as an invasive plant in South Florida and a caution plant in Central Florida.
Invasive plants should not be planted in home gardens because they spread to wild areas and displace native species. Caution plants may be planted in home gardens but should be managed to prevent escape into natural areas.
Any plant you purchase from a nursery should be Senna bicapsularis, but it's a good idea to double-check that you aren't buying the invasive Senna pendula var. glabrata.
Senna bicapsularis has 3 pairs of leaflets on each leaf and flower stalks that are 0.12–0.2 inches long, while Senna pendula has 4–7 pairs of leaflets on each leaf and flower stalks that are 0.08 inches or longer.
For more information, contact your county Extension office.