Sunn hemp Crotalaria juncea
Sunn hemp (Crotalaria juncea) is an annual herb in the Fabaceae family, native to South Asia. It grows 1.5–3 m (4.9–10 ft) tall and 30–60 cm (12–24 in) wide, wants full sun and low water, and is hardy to about 3 °C (37 °F). Space plants about 10 cm (4 in) apart.
Plan Sunn hemp in your garden →
Free. Draw your beds, then watch it grow through the year in 2D and 3D.
Sunn hemp at a glance
| Type | Annual herb |
|---|---|
| Family | Fabaceae |
| Mature height | 1.5–3 m (4.9–10 ft) |
| Mature spread | 30–60 cm (12–24 in) |
| Spacing | 10 cm (4 in) centre to centre |
| Sun | Full sun, at least 6 h of direct sun a day |
| Water | Low; drought tolerance moderate, waterlogging tolerance none |
| Soil pH | 5–7.5 |
| Cold hardiness | About 3 °C (37 °F) once established (roughly USDA zone 10) |
| Heat stress | Likely above about 38 °C (100 °F) |
| Flowering | about 7–10 weeks after planting, for 3–4 weeks |
| Days to maturity | About 90 days from planting |
| Wind tolerance | Low |
| Pollinator value | Moderate |
| Edible | Not grown as food |
| Native to | South Asia |
| Common in gardens of | 🇮🇳 India, 🇹🇭 Thailand, 🇧🇷 Brazil, 🇺🇸 United States |
Is Sunn hemp toxic?
- People: moderately toxic
- Cats: moderately toxic
- Dogs: moderately toxic
- Parts: seeds
Seeds hold pyrrolizidine alkaloids, harmful to 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 Sunn hemp
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 Sunn hemp
- How far apart should I plant Sunn hemp?
- About 10 cm (4 in) apart, centre to centre. A mature plant spreads 30–60 cm (12–24 in).
- Does Sunn hemp need full sun?
- Full sun: at least 6 hours of direct sun a day.
- How much water does Sunn hemp need?
- Low water. Drought tolerance is moderate and waterlogging tolerance none.
- How cold-hardy is Sunn hemp?
- It tolerates about 3 °C (37 °F) once established, roughly USDA zone 10. As an annual it is usually planted out after the last frost.
- When does Sunn hemp flower?
- About 7–10 weeks after planting, for 3–4 weeks.
- Is Sunn hemp poisonous to cats and dogs?
- For cats it is moderately toxic; for dogs moderately toxic; for people moderately toxic. Seeds hold pyrrolizidine alkaloids, harmful to livestock.
- What grows well with Sunn hemp?
- "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 C (C: plausible, mixed evidence).
- EcoCrop crop environmental requirements, FAO
- Agroforestree Database, World Agroforestry (ICRAF)
Notes and assumptions
- Grown to feed the soil: cut or dig it in at flowering, before it turns woody or sets seed.
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