Siamese cassia (khi lek) Senna siamea
Siamese cassia (khi lek) (Senna siamea) is an evergreen perennial tree in the Fabaceae family, native to Mainland Southeast Asia (Thailand, Myanmar, Indochina) and possibly Sri Lanka. It grows 10–18 m (33–59 ft) tall and 6–10 m (20–33 ft) wide, wants full sun and low water, and is hardy to about 5 °C (41 °F). Space plants about 8 m (26 ft) apart.
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Siamese cassia (khi lek) at a glance
| Type | Perennial tree, evergreen |
|---|---|
| Family | Fabaceae |
| Mature height | 10–18 m (33–59 ft) |
| Mature spread | 6–10 m (20–33 ft) |
| Spacing | 8 m (26 ft) centre to centre |
| Sun | Full sun, at least 6 h of direct sun a day |
| Water | Low; drought tolerance high, waterlogging tolerance none |
| Soil pH | 5.5–8 |
| Cold hardiness | About 5 °C (41 °F) once established (roughly USDA zone 11) |
| Heat stress | Likely above about 42 °C (108 °F) |
| Flowering | from about October for 13–26 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | Moderate |
| Pollinator value | High |
| Edible | Yes: young leaves and flower buds (only after repeated boiling; kaeng khi lek curry) |
| Native to | Mainland Southeast Asia (Thailand, Myanmar, Indochina) and possibly Sri Lanka |
| Common in gardens of | 🇹🇭 Thailand, 🇮🇳 India, 🇮🇩 Indonesia, 🇲🇾 Malaysia, 🇰🇪 Kenya, 🇳🇬 Nigeria |
Is Siamese cassia (khi lek) toxic?
- People: moderately toxic
- Cats: not well documented
- Dogs: moderately toxic
- Parts: leaves, pods, seeds
Leaves contain barakol: Thai cooks boil them several times before making curry, which removes most of it. Leaf-powder capsules sold as a sleep aid were withdrawn in Thailand in 2003 after cases of hepatitis. The leaves and pods are poisonous to pigs and some other livestock.
If a child or pet may have eaten part of a plant, call a poison centre or vet straight away.
Companion planting: what to grow with Siamese cassia (khi lek)
Good neighbours
- good With Sweet corn: "Three sisters": climbing beans use corn as a support and fix nitrogen; the benefit to the corn is modest but real in low-input soils. Evidence C
Keep apart or take care
- caution With Alliums (onion family): Onions, garlic and leeks are said to stunt beans and peas (allium root exudates may reduce nodulation). Traditional companion-planting advice; controlled trials are few, so treat it as a soft preference. Evidence D
- caution With Alliums (onion family): Beans and peas are traditionally kept away from onions, garlic and leeks. Traditional companion-planting advice; controlled trials are few, so treat it as a soft preference. Evidence D
- caution With Fennel: Fennel is reported to suppress beans and peas growing next to it. Evidence C
Questions about Siamese cassia (khi lek)
- How far apart should I plant Siamese cassia (khi lek)?
- About 8 m (26 ft) apart, centre to centre. A mature plant spreads 6–10 m (20–33 ft).
- Does Siamese cassia (khi lek) need full sun?
- Full sun: at least 6 hours of direct sun a day.
- How much water does Siamese cassia (khi lek) need?
- Low water. Drought tolerance is high and waterlogging tolerance none.
- How cold-hardy is Siamese cassia (khi lek)?
- It tolerates about 5 °C (41 °F) once established, roughly USDA zone 11.
- When does Siamese cassia (khi lek) flower?
- From about October for 13–26 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Siamese cassia (khi lek) poisonous to cats and dogs?
- For cats it is not well documented; for dogs moderately toxic; for people moderately toxic. Leaves contain barakol: Thai cooks boil them several times before making curry, which removes most of it. Leaf-powder capsules sold as a sleep aid were withdrawn in Thailand in 2003 after cases of hepatitis. The leaves and pods are poisonous to pigs and some other livestock.
- What grows well with Siamese cassia (khi lek)?
- "Three sisters": climbing beans use corn as a support and fix nitrogen; the benefit to the corn is modest but real in low-input soils.
Sources and evidence
Evidence grade B (B: extension service or peer-reviewed).
- Plants of the World Online (taxonomy, native range), Royal Botanic Gardens, Kew
- PROSEA: Plant Resources of South-East Asia, PROSEA Foundation, Bogor
- CABI Invasive Species Compendium, CABI
Notes and assumptions
- Evergreen, fast and drought-hard; planted across the tropics for shade, firewood and hard dark heartwood. Not a nitrogen fixer, unlike many legume trees.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
Related plants
- Bush bean Phaseolus vulgaris
- Garden pea Pisum sativum
- Sweet pea Lathyrus odoratus
- Runner bean Phaseolus coccineus
- Broad bean (fava) Vicia faba
- Lima bean Phaseolus lunatus
- Cowpea (black-eyed pea) Vigna unguiculata
- Yardlong bean Vigna unguiculata subsp. sesquipedalis