Warm-Season Legume • Cover Crop • Green Manure
Sunn Hemp
Crotalaria juncea
A fast-growing warm-season annual legume used to build biomass, fix nitrogen, suppress weeds, add organic matter, and increase functional diversity in summer cover crop programs.
About Sunn Hemp
Sunn hemp is a warm-season annual legume valued for rapid vegetative growth, nitrogen fixation, biomass production, and its ability to provide dense summer cover.
Unlike true hemp, sunn hemp is a member of the legume family. It develops an upright canopy and extensive root system while forming a symbiotic relationship with nitrogen-fixing rhizobia.
Sunn hemp can be grown as a full-stand green manure or incorporated into diverse warm-season cover crop mixtures where additional nitrogen fixation, biomass, rooting diversity, and weed competition are desired.
Agronomic Benefits
Why Plant Sunn Hemp?
Sunn hemp combines fast summer growth with several complementary soil-health functions.
Nitrogen Fixation
As a legume, properly nodulated sunn hemp can fix atmospheric nitrogen and incorporate nitrogen-rich plant material into the cropping system.
High Biomass
Rapid warm-season growth can produce substantial above-ground material for residue, green manure, and organic matter.
Weed Competition
Fast growth and a tall canopy can shade the soil surface and improve competition against many summer weeds.
Rooting Diversity
Adds a different root architecture to mixtures dominated by fibrous-rooted grasses and cereals.
Nematode Management
Sunn hemp is recognized for suppressive effects against certain plant-parasitic nematodes and can be useful within appropriate crop rotations.
Pollinator Habitat
Yellow flowers can provide floral resources for bees and other insects when plants are allowed to reach bloom.
Establishment
Plant Sunn Hemp in Warm Soil
Sunn hemp is a warm-season species and should be planted after frost risk has passed and soils have warmed. Rapid establishment is favored by warm temperatures, adequate moisture, and good seed-to-soil contact.
A full-stand seeding rate of approximately 40 lb/acre is appropriate for California cover crop use. Rates should be reduced when sunn hemp is included as one component of a multi-species mixture.
Place seed approximately ½–1 inch deep. Avoid planting too deeply, particularly in heavier soils. Sunn hemp performs best in soils with good drainage and should not be established where prolonged waterlogging is likely.
Where Sunn Hemp Fits
Cover Crop & Soil-Building Applications
Green Manure
Produces nitrogen-rich biomass that can be terminated and returned to the soil.
Cover Crop Mixes
Adds warm-season legume diversity to mixes containing grasses, broadleaves, and other legumes.
Weed Suppression
Tall, rapid growth can create competitive summer canopy cover.
Soil Health
Adds roots, residue, organic matter, and biologically fixed nitrogen to the system.
Summer Cover Crop Diversity
A Strong Legume Component for Warm-Season Mixes
Sunn hemp can complement warm-season grasses and broadleaves by adding biological nitrogen fixation and a different rooting and canopy structure.
Weaver Seed can incorporate sunn hemp into custom summer cover crop and soil-building mixtures based on crop rotation, planting window, termination timing, irrigation, and management goals.
Inoculation
For reliable nitrogen fixation, sunn hemp seed should have access to compatible rhizobia. A cowpea-type inoculant is commonly recommended where appropriate bacteria are not already present in the soil.
Livestock Consideration
Sunn hemp cultivars can differ in pyrrolizidine alkaloid content. Do not assume an unknown sunn hemp lot or cultivar is suitable for grazing, hay, or feed. Verify cultivar and intended livestock use before feeding.
Sunn Hemp Seed
Need Sunn Hemp for a Cover Crop or Custom Mix?
Contact Weaver Seed for current sunn hemp availability, wholesale quantities, pricing, and custom warm-season cover crop mixtures.