Sunn hemp, Crotalaria juncea, is one of India’s oldest fibre crops and a fast-growing green manure. It has nothing to do with cannabis, despite the name hemp. Its tall stems give a strong bast fibre for ropes, nets and paper, and farmers plough it into the soil to add nitrogen. Its bright yellow flowers make sunn hemp fields easy to spot.
- Botanical name
- Crotalaria juncea L.
- Family
- Fabaceae
- Tamil
- Sanappu
- Hindi
- San
- Parts used
- Bast fibre, Green manure
- Habit
- Sunn hemp; hemp is a shop word
- Last updated
- 2026-10-26
How to recognise Sunn hemp
It is an upright annual, two to three metres tall, with simple, narrow, silvery-hairy leaves.
It grows very fast, reaching full height in about two months.
Large bright yellow pea-flowers grow in long spikes at the top of the stems.
The pods are inflated and hairy, and the seeds rattle inside when dry.
Rattleweed, Crotalaria retusa, is a smaller weed with wedge-shaped leaves and more toxic seeds.
Traditional use of Sunn hemp
Fibre
Sunn fibre is retted from the stems and used for ropes, fishing nets, twine and paper, especially cigarette paper.
Indian fibre practice
Green manure
Farmers sow sunn hemp before rice or other crops and plough it in at flowering to enrich the soil.
Indian farm practice
Modern notes on Sunn hemp
As a green manure it adds large amounts of nitrogen and organic matter and suppresses some soil nematodes.
Its seeds contain alkaloids, though less than rattleweed, so they should not be fed to livestock in quantity.
Sunn hemp safety
Do not eat the seeds or feed them in bulk to animals.
Ecology and sourcing
It is thought to have originated in India and is grown across the tropics.
It grows quickly in heat and drought, smothering weeds.
Bees and butterflies visit its flowers.
Related plants
Also in Fabaceae
Questions about Sunn hemp
Is Sunn hemp related to cannabis?
No. It is a legume; hemp is just a fibre name.
What is green manure?
A crop ploughed into the soil to enrich it.
Is Sunn hemp rattleweed?
No. Rattleweed is Crotalaria retusa.
Where is Sunn hemp grown in India?
Across the plains, in both the monsoon and the dry season, as fibre or green manure.
Sources
- Crotalaria juncea L. — Plants of the World Online, Kew (search) (accessed 2026)
- Wikidata item Q2855436 (Crotalaria juncea)
Educational page about a plant. It is not medical advice, not a diagnosis, and not an offer to sell. Traditional use is historical. If you need care, ask a licensed clinician. Questions: hello@meevamed.com.