Germination temperature
Warm: about 20-30 °C (68-86 °F); very poor at 10 °C (50 °F).
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Sickle senna, also called chakvad or Cassia tora, is a fast-growing warm-season legume grown for its leaves and seeds. Its seeds have a hard, waterproof coat, so scarifying them before sowing makes the difference between a few scattered seedlings and an even stand.
Warm: about 20-30 °C (68-86 °F); very poor at 10 °C (50 °F).
About 2-3 cm (3/4-1 1/4 in).
Scarified seed germinates quickly and evenly; untreated seed is slow and erratic.
Not needed for germination; grow in full sun or light shade.
Essential: nick or sand the seed coat, or use a hot-water soak.
Direct sowing is simplest; young seedlings can be moved with care.
Senna tora seed has physical dormancy: the hard seed coat stops water getting in. In a study from Bihar, India, only 20% of untreated Cassia tora seed germinated, while the best pre-treatment (concentrated sulphuric acid followed by gibberellic acid) raised germination to 90%. Mechanical scarification followed by gibberellic acid was almost as effective.
The most reliable home method is mechanical: rub seeds on fine sandpaper or nick each seed coat with a nail clipper or blade, on the side away from the small scar where the root emerges, until the paler inner layer just shows. In trials on five other Senna species, mechanical scarification gave 100% germination in four of them. Acid scarification works equally well but is a laboratory method and not safe at home.
Hot water is an alternative: pour water just off the boil over the seed, let it cool and soak overnight, then sow the seeds that have swollen and re-treat those that stayed hard. Test a small batch first: boiling water raised germination to 82-98% in some Senna species but reduced it in another.
Not needed. Dormancy is in the seed coat, not the embryo, so cold treatment does not help.
Aim for 20-30 °C (68-86 °F). Ethiopian Senna species germinated best at about 20-25 °C (68-77 °F) and hardly at all at 10 °C (50 °F); closely related sicklepod (Senna obtusifolia) germinated best between 15 and 30 °C (59-86 °F). In India this means sowing at the start of the warm, wet season.
Sow 2-3 cm (3/4-1 1/4 in) deep. Sicklepod seedlings emerged on average from 3.3-4.6 cm (1 1/4-1 3/4 in) and occasionally from 10 cm (4 in) in sandy loam, so a moderate cover is safe and keeps the seed moist.
Any well-drained soil or seed compost. Sicklepod germinated best near pH 6.
Keep the soil evenly moist after sowing scarified seed; germination falls sharply when the soil dries out.
Light is not required: Senna seeds germinated equally in light and darkness in laboratory tests.
Scarified seed gives quick, uniform germination. Untreated seed may sprout over a long period or not at all, so treat all seed before sowing.
Direct sowing avoids root disturbance. If you start seed in trays, use deep cells and plant out while seedlings are small, keeping the root ball intact.
Sickle senna grows into an erect, shrubby plant 0.5-1.5 m (1 1/2-5 ft) tall. Give it full sun or light shade, well-drained soil and moderate watering; it needs little feeding as a legume.
Plants form long, narrow, curved pods, each with more than 20 brown seeds. Pick pods as they turn dry and brown, before they split.
Cause: seed sown without scarification; the hard coat keeps water out. Fix: sand or nick each seed, or give a hot-water soak, then sow only seeds that have swollen.
Cause: cold or waterlogged soil, or damage from an overly long boiling-water treatment. Fix: sow only in warm soil (above about 20 °C, 68 °F), in free-draining compost, and use water just off the boil rather than continuous boiling.
Cause: uneven scarification, so only some seeds took up water. Fix: check after soaking and re-treat seeds that are still small and hard.
Cause: sickle senna is naturalised as a weed across much of the tropics, and dropped seed stays dormant in the soil. Fix: harvest pods before they open and remove unwanted seedlings early.
In India sow at the beginning of the monsoon or in warm weather; in cooler climates sow indoors in late spring or outdoors after the soil has warmed.
The leaves are edible and used as a herb. Pick young leaves from vigorous plants and leave enough foliage for the plant to flower.
Senna tora seeds and leaves have mild purgative properties and are used in traditional medicine. Use them in modest culinary amounts and seek medical advice before any medicinal use.
Hard, dry seed stores well. Scarify only the seed you are about to sow, because scarified seed takes up moisture and does not keep.
Order Senna tora seeds and sow them, scarified, at the start of the warm season.
The seed coat is hard and waterproof. Untreated seed germinated only about 20% in an Indian study. Sand or nick each seed, or soak in water poured just off the boil, and sow in warm soil.
Sandpaper or nicking is the most reliable, because each seed is opened. Hot water treats many seeds at once, but its effect varies between Senna species, so test a few seeds first.
Yes. Cassia tora L. is the older name; the accepted botanical name is Senna tora (L.) Roxb. It is a different species from American sicklepod, Senna obtusifolia.