With fertiliser prices remaining volatile, many Australian farmers are looking for practical ways to reduce input costs without sacrificing productivity.
One crop attracting renewed attention is Sunn Hemp (Crotalaria juncea) — a fast-growing tropical legume capable of fixing nitrogen, producing valuable biomass, improving soil structure and helping suppress weeds.
Recent coverage by ABC Rural highlighted growers using Sunn Hemp to reduce their reliance on urea fertiliser, showing how cover crops can play an important role in more profitable farming systems.
Whether you are growing broadacre crops, vegetables, sugarcane, pasture or cover crops, Sunn Hemp is increasingly proving itself as more than just a green manure crop.
What Is Sunn Hemp?
Sunn Hemp is a vigorous annual legume grown primarily as a:
- green manure crop
- nitrogen-fixing cover crop
- soil improver
- biomass producer
- weed suppressor
Despite the name, Sunn Hemp is not the same as industrial hemp. It is a different plant species grown for its agricultural and soil-building benefits.
In warm conditions, Sunn Hemp establishes rapidly and can produce a large volume of organic matter in just 8–12 weeks.
Why Farmers Are Planting More Sunn Hemp
The biggest driver is simple: nitrogen fertiliser is expensive.
Rather than relying solely on manufactured fertiliser, legumes work with beneficial soil bacteria to capture atmospheric nitrogen and convert it into forms future crops can use. This process is known as biological nitrogen fixation.
When Sunn Hemp is incorporated back into the soil, much of the nitrogen and organic matter becomes available to support following crops.
Instead of buying every kilogram of nitrogen, farmers can use legumes like Sunn Hemp to naturally supply part of their crop’s nitrogen requirement.
Reducing Reliance on Urea
One reason Sunn Hemp is receiving attention is its potential to help reduce fertiliser inputs.
Although every farming system is different, many growers use Sunn Hemp between cash crops to:
- reduce purchased nitrogen requirements
- increase soil organic matter
- improve water infiltration
- recycle nutrients
- reduce erosion
- stimulate beneficial soil biology
For growers facing rising fertiliser costs, these benefits can translate into meaningful savings over time.
Additional Benefits of Sunn Hemp
Excellent Weed Suppression
Sunn Hemp grows quickly in warm conditions, shading the soil and helping suppress many annual weeds before they become established.
Large Biomass Production
Sunn Hemp produces a large volume of leafy biomass that breaks down relatively quickly after incorporation. This adds organic matter and helps improve soil structure.
Improved Soil Health
Repeated use of cover crops such as Sunn Hemp can help:
- increase soil carbon
- improve soil aggregation
- reduce compaction
- increase microbial activity
- improve moisture retention
Supports Sustainable Farming
By integrating legumes into crop rotations, growers can build healthier soils while reducing dependence on synthetic fertilisers.
When to Plant Sunn Hemp in Australia
Sunn Hemp is a warm-season crop. For most regions, it performs best when soil temperatures are consistently warm, generally above 18–20°C.
| Region | Recommended Planting Time |
|---|---|
| Northern Australia | September – February |
| Queensland | September – January |
| Northern New South Wales | October – January |
| Southern Australia | Late Spring – Summer |
It grows best in full sun and well-drained soil.
How Long Does Sunn Hemp Take to Grow?
Under favourable conditions, Sunn Hemp establishes quickly and produces strong canopy growth within a few weeks.
For green manure use, the crop is commonly incorporated after around 8–12 weeks, before stems become overly woody.
Does Sunn Hemp Fix Nitrogen?
Yes. Like many legumes, Sunn Hemp forms nodules on its roots that contain beneficial nitrogen-fixing bacteria.
These bacteria capture atmospheric nitrogen and convert it into plant-available forms.
For maximum nitrogen fixation, seed should be inoculated with the appropriate rhizobium inoculant where required.
Is Sunn Hemp Suitable for Australian Farms?
Sunn Hemp is suitable for a wide range of Australian growing systems, including:
- vegetable growing
- market gardening
- mixed farming
- regenerative agriculture
- sugarcane rotations
- grazing enterprises
- orchard inter-rows
- cover cropping systems
Its rapid growth and adaptability make it one of Australia’s most useful summer green manure crops.
Frequently Asked Questions
What is Sunn Hemp used for?
Sunn Hemp is primarily used as a nitrogen-fixing cover crop, green manure and soil improver.
Is Sunn Hemp edible?
No. Sunn Hemp is grown for soil improvement rather than human consumption.
Is Sunn Hemp the same as industrial hemp?
No. Sunn Hemp (Crotalaria juncea) is a different plant species grown for agricultural and soil-building purposes.
Does Sunn Hemp need inoculation?
In many situations, yes. Using the correct rhizobium inoculant helps maximise nitrogen fixation.
Why Buy Sunn Hemp Seed from Seedmart?
Seedmart supplies high-quality Sunn Hemp seed suitable for Australian growing conditions.
Whether you are improving degraded soils, reducing fertiliser costs or introducing cover crops into your rotation, Sunn Hemp offers one of the fastest ways to build biomass and naturally add nitrogen to the soil.
Shop Sunn Hemp Green Manure Seeds
As fertiliser prices continue to challenge Australian agriculture, growers are increasingly looking for practical ways to improve profitability.
Sunn Hemp offers a valuable combination of nitrogen fixation, rapid biomass production and soil improvement, making it an excellent addition to many farming systems.
Whether you are managing a broadacre enterprise, market garden or regenerative farming operation, incorporating Sunn Hemp into your crop rotation can help build healthier soils while reducing dependence on purchased nitrogen.