Sunn Hemp Cover Crop Seeds

Sunn Hemp Cover Crop Seeds

Botanical Name: Crotalaria juncea

Sunn Hemp is a fast-growing warm-season legume grown as a cover crop for nitrogen fixation, biomass production, weed suppression and soil improvement. It is also widely used as a green manure crop. It grows quickly in warm conditions, produces strong upright stems and develops a deep root system that helps improve soil structure and add organic matter.

As a soil-building cover crop, Sunn Hemp is suitable for summer vegetable rotations, orchards, food forests, broadacre cover cropping, regenerative farming and soil-building blends. It can be chopped and incorporated into the soil before flowering, or cut and left on the surface as mulch in no-dig systems.

• Fast-growing warm-season legume cover crop and green manure.
• Can fix atmospheric nitrogen when compatible rhizobia are present; an appropriate inoculant may improve nodulation.
• Produces high biomass for chop-and-drop mulch or soil incorporation.
• Helps suppress weeds by forming quick, dense summer growth.
• Deep roots can contribute to soil structure and organic matter as plant residues decompose.
• Useful for vegetable beds, orchards, food forests, paddocks and regenerative farming.
• Best suited to warm, frost-free growing periods.

Plant Details

• Plant Type: Warm-season annual legume cover crop
• Botanical Name: Crotalaria juncea
• Growth Height: Approximately 1–2.5 m depending on conditions
• Growth Habit: Upright, fast-growing annual
• Root System: Deep taproot with nitrogen-fixing potential
• Frost Tolerance: Low; frost sensitive
• Drought Tolerance: Moderate to good once established
• Best Position: Full sun
• Important Note: Primarily grown for cover cropping and soil improvement; not recommended for general livestock grazing without variety-specific safety advice.

Best Uses

• Green manure crop
• Warm-season cover crop
• Nitrogen fixation
• Weed suppression
• Chop-and-drop mulch
• Summer soil improvement
• Orchard and food forest inter-rows
• Vegetable garden rotations
• Regenerative farming and cover crop blends

Sowing Information

• Best Sowing Time: Spring to summer once soil is warm and frost risk has passed
• Germination Time: 3–10 days in warm, moist soil
• Sowing Depth: 1–2 cm
• Position: Full sun
• Soil Type: Well-drained soil; performs well in sandy loam, loam and lighter soils
• Watering: Keep moist during germination; more drought tolerant once established
• Inoculation: For best nitrogen fixation, use a suitable cowpea-type legume inoculant where available.

Sowing Rate and Coverage

Seed Quantity Guide

Coverage is a guide only. Coverage is approximate and depends on establishment, seed quality and site conditions; adjust sowing rates to local agronomic advice.

When to Sow Sunn Hemp in Australia

How to Sow Sunn Hemp Seeds

1. Choose a warm, sunny position with well-drained soil.
2. Remove weeds and prepare a firm seedbed.
3. Broadcast seed evenly or sow in rows 20–30 cm apart.
4. Cover seed with approximately 1–2 cm of soil.
5. Press or roll lightly for good seed-to-soil contact.
6. Water well after sowing if soil moisture is low.
7. Keep moist until seedlings are established.

Management

• Sow into warm soil for fastest establishment.
• Keep moist during germination and early growth.
• Cut before plants become too woody if incorporating as green manure.
• Cut before heavy seed set if volunteers are not wanted.
• Use in warm-season green manure blends for added diversity.
• Leave chopped material on the surface as mulch in no-dig systems.

Harvest and Incorporation

For green manure use, cut Sunn Hemp when plants are around 60–100 cm tall or before stems become overly woody. Incorporate the chopped material into the soil 2–3 weeks before planting the next crop, or leave it on the surface as mulch.

Earlier cutting produces softer material that breaks down faster, while later cutting produces more biomass and longer-lasting mulch.

Soil Benefits and Use

Sunn Hemp is valued as a cover crop for its nitrogen-fixing potential, fast summer biomass, weed suppression and soil improvement. Its roots help improve soil structure, while the above-ground growth provides organic matter when chopped and returned to the soil.

It is especially useful in vegetable rotations, orchards, food forests, broadacre cover cropping and regenerative farming systems.

Important Notes

• Sunn Hemp is frost sensitive and should be sown only after frost risk has passed.
• Primarily intended for cover cropping and green manure, not general livestock grazing; do not graze without variety-specific safety advice.
• For best nitrogen fixation, use a suitable legume inoculant where available.
• Cut before stems become too woody if quick breakdown is desired.
• Do not allow plants to set seed unless volunteer plants are acceptable.

Quick Growing Guide