Senna surattensis Seeds | Senna
LATIN NAME: Senna surattensis
COMMON NAME: Senna, Golden Cassia, Glaucous Cassia
Plant Profile
Golden Cassia is an evergreen flowering shrub of South and Southeast Asia, growing to four or five metres with a rounded crown and graceful, feathery leaves of paired oval leaflets. Through most of the year it carries flat heads of golden-yellow flowers, which has made it a standard street and garden plant across the tropics.
It grows fast in warm, humid conditions, flowers from an early age, and sets flat, papery pods in quantity. It is tender: anything below about 5 °C checks it, and frost will cut it to the ground, so in temperate gardens it is a pot plant for a bright conservatory. In strong light the young foliage carries a faint glaucous bloom that freshens the shrub between the waves of flowers.
Science & Biotechnology
The genus Senna was split from Cassia on the strength of its asymmetric flowers and the absence of the bark-rich chemistry of the true cassias. The sennosides that make senna a standard laxative come from two other species, chiefly S. alexandrina, not from this ornamental; the confusion is worth clearing up because the names overlap in older writing.
Like many legumes its seed is hard-coated and can lie dormant for years, which is why scarification rather than patience is the practical answer. Its flowers are asymmetric, with one large fertile stamen and reduced others, the floral signature the taxonomists used when they took Senna out of Cassia.
Uses & Benefits
In frost-free gardens it is a quick, long-flowering shrub for borders, hedges and streetscapes, attractive to bees and sunbirds through most of the year. Its crown gives light shade, and its pods are taken by birds and small mammals.
In temperate gardens it is a summer-flowering container plant that can be overwintered frost-free, though it needs space, since it grows strongly in a pot too. In its home range it is planted along roads and in school compounds, where its constant flowers cost almost nothing to maintain, and children learn its pods as a seed-collecting staple. A single pot plant will carry a dozen heads at once in its third year, enough to justify its winter floor space.
Growing from Seed
Nick the hard seed coat or soak the seed in hot water overnight, sowing the seeds that swell.
Sow a centimetre deep in a warm, free-draining mix at 25 °C; germination takes one to three weeks.
Grow the young shrubs in full sun, pot them on as they fill the container, and pinch them once or twice to build a bushy shape before the first flowering. Feed sparingly, since it flowers better on the lean side and overfed plants make leaf at the expense of the golden heads; a slow-release feed in spring is plenty. In frost-free ground, plant it out at the start of the rains. Repot every second year rather than annually, since the roots fill a pot quickly but resent disturbance when they have just filled it.
Our Take
A near-perpetual yellow-flowering shrub for the tropics or a bright conservatory, fast from scarified seed and easy to keep in shape.
Related Reading
Gardeners who grow Senna often pair it with these related subjects: