Senna alata Demystified: From Growth to Garden Brilliance

Senna alata, also known as “Candle Bush” and “Winged Senna,” belongs to the pea family and is a shrub that reaches heights of 1.5-3 meters.

Its branches are robust and green. The leaves are thinly coriaceous, in oblong-ovate or elongated shapes. The plant boasts terminal and axillary inflorescences with long peduncles.

The pod fruit is long and band-shaped, with the flowering season spanning from November to January and the fruiting season from December to February.

Each inflorescence, solitary or branched, stretches 10-50 cm in length; flowers are about 2.5 cm in diameter, initially enveloped by elongated oval, membranous bracts. The petals are yellow with distinct purple veins.

The upper three stamens are reduced while the seven lower ones are developed, with the bottom two bearing larger anthers and the side ones smaller.

Native to the tropical regions of the Americas, the Candle Bush’s bracts, buds, and petals share a striking yellow hue, making the entire inflorescence a spectacle of ornamental value. It’s also a medicinal plant, used as a laxative and vermifuge for its seeds.

I. Morphological Characteristics

Senna alata is an erect shrub, reaching 1.5-3 meters in height with robust green branches. Its leaves are 30-60 cm long, with two longitudinal ridges and narrow wings on the petiole and rachis, and triangular stipules.

There are 6-12 pairs of leaflets, thin-leathery, oblong-ovate or elongated, 8-15 cm long and 3.5-7.5 cm wide, with bluntly rounded tips and oblique bases. The veins on the underside are pronounced, and the petiolules are extremely short or nearly absent.

The inflorescences are terminal and axillary, with long peduncles, solitary or branched, 10-50 cm in length. Flowers, about 2.5 cm in diameter, are initially covered by elongated oval, membranous bracts.

The petals are yellow with clear purple veins. The pod fruit is long and band-shaped, 10-20 cm in length and 1.2-1.5 cm wide, with blunt-toothed, papery wings extending from the top center to the base.

Each pod contains 50-60 flat, triangular seeds. The blooming period is from November to January, and the fruiting season is from December to February.

II. Growing Environment

The Candle Bush thrives in open woodlands or on drier slopes. It is drought-tolerant, thrives in poor soil, and is highly adaptable. Preferring sunlight to partial shade, it enjoys a high-temperature, moist climate, but is not cold-hardy or resistant to strong winds.

III. Distribution

Senna alata is native to the tropical regions of the Americas.

IV. Growth and Propagation

Cutting Propagation

After the onset of warm spring weather, cuttings from either tender new growth or last year’s mature branches are suitable for propagation.

Insert the cuttings directly into containers filled with potting soil or into a planting bed. After the cuttings have rooted, transplant them two to three times to encourage robust plant growth.

Seed Propagation

Seeding can be done in both spring and autumn, although germination rates are generally higher in spring. The fresher the seeds, the better.

Pre-soak the seeds in hot water at 60°C before planting. Cover the seeds with about 2cm of soil after sowing and water regularly to maintain soil moisture.

Once germinated, water every three to four days and transplant once. Depending on growth, apply a light fertilizer two to three times.

V. Pest and Disease Control

Disease: Sooty mold can be treated in its early stages by spraying with a 500-800 dilution of 50% carbendazim solution once a week for 2-3 consecutive weeks.

Pests: Occasional infestations of powdery mildew and scale insects, which can lead to sooty mold, can be controlled by applying a 2000-fold dilution of fenobucarb.

VI. Main Value

Garden Use

With its bracts, buds, and petals all sporting a vivid yellow, the Candle Bush’s inflorescence is highly ornamental. It is well-suited for mass or scattered planting in gardens, along forest edges, roadsides, and lake shores.

Medicinal Value

The Candle Bush serves medicinal functions, acting as a mild laxative and effective against roundworms with its seeds.