Sunn Hemp

Build Soil Between Cash Crops

Sunn Hemp gives growers an opportunity to put otherwise open summer ground to work. Its rapid growth creates above-ground biomass while its root system contributes below-ground organic material. As a legume, Sunn Hemp can also fix atmospheric nitrogen, making it especially attractive for rotations where improving soil fertility and reducing bare-ground periods are priorities. USDA-NRCS notes that cover crops can improve nutrient cycling, organic matter, erosion protection, water infiltration, and overall soil health.

Sunn Hemp is an excellent option for:

• Summer cover crops
• Soil-building programs
• Crop rotations
• Green manure
• Multi-species cover crop blends
• Fields needing additional residue
• Nitrogen-fixing cover crop programs

Put a Summer Legume to Work

One of the biggest reasons growers plant Sunn Hemp is its ability to fix atmospheric nitrogen through a symbiotic relationship with rhizobia bacteria.

When properly inoculated and established, that makes Sunn Hemp more than just ground cover. It can contribute nitrogen-rich biomass that becomes available to the cropping system as plant material decomposes.

USDA research describes Sunn Hemp as capable of fixing substantial nitrogen in a relatively short 60–90 day growing period, although actual nitrogen contribution varies considerably with stand establishment, growing conditions, biomass, and termination timing.

Benefits

• Adds a legume to crop rotations
• Fixes atmospheric nitrogen
• Produces nitrogen-rich residue
• Helps build soil organic matter
• Improves crop diversity
• Can reduce dependence on applied nitrogen in some cropping systems

Why Choose Sunn Hemp Seed?

Fast Summer Growth

Sunn Hemp establishes quickly under favorable warm-season conditions, allowing growers to produce meaningful cover in a relatively short planting window. USDA describes it as a very quick-growing cover crop.

Excellent Nitrogen Fixer

As a summer annual legume, Sunn Hemp can capture atmospheric nitrogen and incorporate it into plant biomass.

High Biomass Potential

Sunn Hemp can produce substantial above-ground growth. In an NRCS guide for north-central West Texas and southwestern Oklahoma, Sunn Hemp was listed with approximately 5,000–7,000 pounds per acre of biomass potential under the conditions represented by that guide.

Helps Suppress Weeds

Rapid canopy development can shade the soil surface and compete with unwanted vegetation. NRCS identifies weed suppression as one of Sunn Hemp’s useful cover-crop characteristics.

Adds Organic Matter

The combination of roots, stems, and leaves provides substantial plant material that can be returned to the soil following termination.

Excellent in Cover Crop Blends

Sunn Hemp can be mixed with grasses, brassicas, and other legumes to create a more diverse warm-season cover crop. NRCS Texas specifically lists small grains, brassicas, and other legumes as potential mixture partners.

A Warm-Season Option for Southern Plains Cover Crop Programs

Sunn Hemp’s warm-season growth habit makes it particularly interesting for growers looking to establish cover during the hottest part of the cropping season.

For West Texas producers, it can fit into summer cover-crop programs where the goal is to establish a legume component alongside species such as cowpeas, sorghum-sudangrass, millet, sunflower, or other warm-season cover crops.

A USDA-NRCS guide specifically evaluating summer cover crop species adapted to north-central West Texas and southwestern Oklahoma identified Sunn Hemp as a soil builder, nitrogen source, erosion-control crop, and weed-suppression option.

Sunn Hemp Planting Recommendations

Plant Sunn Hemp after soils have warmed and the danger of frost has passed. Seed should be placed into a firm, well-prepared seedbed with adequate seed-to-soil contact.

General Planting Information

• Planting Season: Late spring through summer
• Planting Depth: Approximately ½–1 inch
• Growth Habit: Warm-season annual legume
• Inoculant: Cowpea-type inoculant is commonly recommended
• Termination: Mowing, tillage, appropriate herbicides, or frost depending on the production system

USDA-NRCS guidance lists a ½–1 inch planting depth for Sunn Hemp.

Seeding Rate

Sunn Hemp seeding rates vary substantially according to location, planting method, seed size, stand objective, and whether it is planted alone or in a mixture.

For example, an NRCS guide developed for north-central West Texas and southwestern Oklahoma lists 15 lb./acre for Sunn Hemp, while NRCS trials and recommendations in other regions use substantially higher rates.

For that reason, we recommend choosing a seeding rate based on your field, planting method, and intended use rather than treating one national rate as appropriate everywhere.

Contact Jack Seed & Supply for a Sunn Hemp seeding recommendation for your acreage and cover-crop goals.

What Does Sunn Hemp Bring to the Field?

Crop Type: Warm-season annual legume

Primary Uses: Cover crop, green manure, nitrogen fixation, biomass, soil improvement

Growth: Rapid during warm conditions

Planting Depth: ½–1 inch

Nitrogen Fixation: Very Good

Quick Growth: Very Good

Erosion Control: Good

Soil Building: Excellent use case

Weed Suppression: Useful with adequate stand density

Residue: Can produce substantial plant material

Winter Hardiness: Frost-sensitive annual

NRCS describes Sunn Hemp as a quick-growing summer annual legume with strong nitrogen-fixation ability and benefits for soil health, residue production, erosion control, and weed suppression.

What is Sunn Hemp?

Sunn Hemp is a fast-growing tropical/subtropical annual legume used primarily as a cover crop, green manure, nitrogen-fixing crop, and soil-building species.

Is Sunn Hemp a true hemp plant?

No. Despite the name, Sunn Hemp is not cannabis. Its scientific name is Crotalaria juncea, and it belongs to the legume family.

Does Sunn Hemp add nitrogen to the soil?

Sunn Hemp is a nitrogen-fixing legume. The amount of nitrogen ultimately contributed to the cropping system depends on stand establishment, biomass production, growing conditions, and how the cover crop is managed.

How deep should Sunn Hemp be planted?

A general planting depth is approximately ½ to 1 inch.

Is Sunn Hemp good for West Texas?

It can be a useful warm-season cover crop option. USDA-NRCS has specifically included Sunn Hemp in guidance for summer cover crops adapted to north-central West Texas and southwestern Oklahoma.

Can Sunn Hemp be planted in a cover crop mix?

Yes. Sunn Hemp works particularly well as the legume component of diverse warm-season cover crop blends.