Plant of the Month – October, 2007
At a glance:
Latin Name: Cassia splendens
Common Name: autumn cassia or flowery senna
Flowers: Bright yellow
Foliage: Fine-textured, medium-green. Semi-evergreen.
Mature height: 5-10 feet
Hardiness: Zone 7 south herbaceous perennial to subshrub.
Exposure: Full sun to light afternoon shade
Water usage: Medium
Sources: Mail-order or Internet, local nurseries
Mention fall flowers and everyone immediately thinks of mums, marigolds and salvias. But I think of Cassia splendens!
This shrub will stop you in your tracks with its fantastic fall flowers. Beginning in late September, large clusters of pure yellow flowers cover this plant until first frost. Monarch butterflies flock to it along their fall migration route.
This subtropical plant is a small tree in Zones 9 and 10. In Zone 8 gardens you may lose the foliage occasionally during severe weather (below 15 F). In Zones 7 and northward, it will freeze to the ground at temperatures below 10 F.
I’ve had good luck with it returning yearly and flowering at about 5 feet tall. Occasionally my plant has not returned after winter, but for the amount of flowers I get from my initial purchase, I’d still use this plant like an annual! If it isn’t hardy in your area try planting 1-gallon containers now and they will be 4 to 5 feet tall and wide by fall, and will produce more flowers than any chrysanthemum.
C. splendens makes an incredible backdrop for other fall-flowering perennials, such as Salvia leucantha and Aster oblongifolius. I have also had wonderful results using this plant in large containers. The bright-green foliage and mounding habit looks good all summer. If plants become too large, an occasional pruning will keep them more compact.
Autumn cassia is exceptionally easy to grow, requiring only full sun and well-drained soil to succeed. For fastest growth, a monthly application of fertilizer will help plants size up before fall.
If this plant interests you I recommend planting it soon. The earlier they get into the garden, the more flowers you’ll get this fall, and also the plants will have more time to establish before winter sets in.
To see this plant and many others, visit the Dallas Arboretum at 8525 Garland Rd., Dallas. For more information visit www.dallasarboretum.org or call (214) 515-6500.
About the author: Jimmy Turner is the Director of Horticulture Research at the Dallas Arboretum. For more plant profiles by Jimmy, subscribe to Neil Sperry’s GARDENS Magazine.