Annual Sunn Hemp Pasture, Forage, and Cover Crop Seed

Sunn Hemp Seeds


Latin Name: Crotalaria juncea L.

Season: Annual

Height: 36 - 108 inches

Environment: Full sun

USDA Zones: 8 - 11

Sunn hemp (Crotalaria juncea L.) - is a legume commonly used as a cover crop for southern and sub-tropical and tropical farming systems. It has recently been more adopted in the Midwestern United States cropping systems. Sunn hemp is a tall, shrubby plant – and can reach up to nine feet high! It’s an annual crop that creates a lot of biomass, along with well-developed root systems. It’s deep-yellow flowers produce tiny seeds – so tiny that one pound can contain over 15,000 seeds! It has been utilized as a green manure, livestock feed and as a non-wood fiber crop. 

Because it is a legume, sunn hemp pulls atmospheric nitrogen and puts it into the soil – a process called nitrogen fixation. This leaves the soil with more nitrogen (a necessary nutrient for crops) than before the sunn hemp was grown. Sunn hemp has been extensively used as a soil improvement crop. Its enormous potential to produce biomass and fix nitrogen is crucial to build up soil organic matter and sequester carbon. Sunn hemp possesses many soil-building traits, including high rates of biomass production — over 20 percent greater than crimson clover and hairy vetch in research trials. It is not only resistant to plant root nematodes but actively suppresses them. In as little as 60 to 90 days it can produce 120 pounds of nitrogen per acre and can suppress weeds up to 90 percent.

Sunn Hemp is adapted to a wide variety of soil and environmental conditions, thriving through hot, dry summers and continuing to grow until the first frost. But sunn hemp isn’t just a soil builder — it also offers benefits as a forage producer. Recent on-farm grazing trials have yielded an abundance of information on using this crop for grazing. Sunn hemp is easy to grow and amazingly productive. Plant when soils reach above 50°F and at least four to five weeks before frost. Plants will be killed when temperatures dip below 28°F. Optimal soil conditions include a pH between 5 and 7.5 and good drainage.

For forage production, a seeding rate of 25 - 50 pounds per acre is recommended if seed is broadcasted. Reduce rate for drilling. Seed should be drilled at ½-inch depth for best germination. Because plants can reach 3 to 9 feet in height, wide spacing between rows (6 inches is recommended) may make plants susceptible to lodging. With adequate moisture, temperature and fertility, researchers have recorded a growth rate of 1 foot per week. Plants can return to or exceed this growth rate if slowed by temporary drought.