Green manure growing guide

Improve Your Soil with Green Manure and Cover Crops

Green manure crops are grown primarily to improve the soil rather than for harvest. They protect bare ground, establish living root systems and produce plant material that can later be cut down, lightly incorporated into the soil or left on the surface as mulch.

Depending on the species selected, green manure and cover crops can increase organic matter, fix nitrogen, suppress weeds, reduce erosion, improve soil structure and support beneficial soil organisms.

They can be used in backyard vegetable gardens, raised beds, market gardens, orchards, vineyards, farms and regenerative landscapes. The best choice will depend on your climate, sowing season, soil condition and intended result.

Why Grow Green Manure Crops?

Increase Organic Matter

Roots and leafy growth return carbon-rich plant material to the soil.

Fix Nitrogen Naturally

Compatible legumes can capture atmospheric nitrogen with the assistance of soil bacteria.

Suppress Weeds

Dense, fast-growing cover reduces the light and space available to unwanted plants.

Reduce Erosion

Roots stabilise soil while foliage softens the impact of wind and heavy rain.

Improve Soil Structure

Fibrous roots and taproots create channels and improve soil aggregation.

Support Soil Biology

Living roots provide food and habitat for beneficial soil microorganisms.

Improve Moisture Retention

Ground cover reduces evaporation, while organic matter improves water-holding capacity.

Rest Growing Areas

A green manure phase provides a productive break between vegetable and field crops.

Green Manure vs Cover Crops

The terms green manure and cover crop are often used interchangeably, although they describe slightly different priorities. Many crops perform both functions.

Green Manure Cover Crop
Usually grown to improve soil fertility and increase organic matter. Usually grown to cover and protect the soil surface.
Often cut down while young and returned to the soil. May be mown, grazed, slashed, rolled, crimped or retained for longer.
Frequently used between vegetable crops or during a rotational break. Frequently used to reduce erosion, suppress weeds and maintain living roots.
Legumes are often selected where nitrogen fixation is the main priority. Grasses, legumes, brassicas and multi-species mixtures may all be used.

In practice: a crop may protect bare soil while it is growing and then function as green manure when its roots and foliage are returned to the soil.

Choosing the Right Green Manure Seed

Begin by identifying the main result you want to achieve. A single species may suit a particular soil problem, while a mixture can provide several complementary benefits.

Your Main Objective Suitable Crops How They Help
Increase nitrogen Clovers, vetches, field peas, cowpeas, lupins and medics Legumes can fix atmospheric nitrogen when compatible rhizobia bacteria are present.
Build biomass Oats, cereal rye, millet and other vigorous grasses Produce substantial root mass and above-ground plant material.
Suppress weeds Buckwheat, cereals and vigorous green manure mixtures Establish quickly and create dense cover over the soil surface.
Improve compacted soil Forage radish, tillage radish and deep-rooted mixtures Strong taproots penetrate firm layers and leave channels after decomposition.
Protect soil in winter Oats, cereal rye, vetch, field peas and winter mixtures Maintain cover during cooler and wetter conditions.
Cover soil in summer Cowpea, millet, buckwheat and other warm-season species Provide rapid growth in warm soil and suitable summer conditions.
Support pollinators Phacelia, flowering clovers and buckwheat Produce flowers that provide forage for bees and beneficial insects.
Increase plant diversity Multi-species green manure mixtures Combine different root depths, growth habits and soil functions.

Types of Green Manure Crops

1

Nitrogen-Fixing Legumes

Clovers, vetches, field peas, cowpeas, lupins and medics are commonly grown to improve nitrogen availability.

They are particularly useful before nitrogen-demanding crops such as leafy vegetables, brassicas and sweet corn.

2

Grasses and Cereals

Oats, cereal rye and millet produce fibrous root systems and substantial above-ground biomass.

They can protect soil, capture residual nutrients and contribute carbon-rich material.

3

Deep-Rooted Soil Conditioners

Forage and tillage radishes develop strong roots that penetrate firm soil layers.

As the roots break down, they leave channels that improve air and water movement.

4

Fast-Growing Flowering Crops

Buckwheat and phacelia can establish quickly under suitable conditions.

Their flowers can provide forage for bees and beneficial insects when allowed to reach flowering.

Important: green manure crops grown primarily for soil improvement should generally be terminated before mature seed forms. This reduces the risk of self-sown plants becoming weeds in the following crop.

Single Species or Green Manure Mix?

Single-Species Crops

A single species is useful when you have one clear objective, a short growing window or want straightforward establishment and termination.

  • Simple sowing and management
  • Predictable growth habit
  • Useful for targeting a specific soil issue
  • Easier to match to a short seasonal window

Multi-Species Mixes

A mixture combines different plant families, root depths and growth habits to provide a broader range of soil benefits.

  • Legumes contribute nitrogen
  • Grasses produce biomass and fibrous roots
  • Brassicas provide strong taproots
  • Flowering species support beneficial insects

When to Sow Green Manure Seeds

Green manure can be planted whenever a garden bed, paddock or growing area would otherwise remain bare. The appropriate crop will depend on the season, local climate and available moisture.

Season General Crop Options Typical Use
Autumn Cool-season cereals, clovers, vetches, field peas and winter mixtures Establish cover before cooler and wetter conditions.
Winter Cold-tolerant cereals and legumes suited to the local climate Protect resting beds and maintain living roots.
Spring Short-duration cool-season crops or warm-season species as the soil heats Prepare soil for summer or fill a gap between plantings.
Summer Cowpea, millet, buckwheat and other heat-tolerant crops Provide rapid cover and biomass during warm conditions.

Australia includes tropical, subtropical, temperate, cool and arid growing regions. Always check the sowing information on the individual product page before selecting a crop.

General Australian Climate Guide

Climate Common Options Points to Consider
Tropical Cowpea, millet and other warm-season species Time planting around rainfall and avoid crops poorly suited to persistent heat.
Subtropical Cowpea, buckwheat, millet, clovers and seasonal mixtures Warm- and cool-season crops may both be suitable at different times of year.
Temperate Oats, vetch, field peas, clovers, rye and summer buckwheat Match the crop to the available autumn, winter or summer growing window.
Cool Cereal rye, oats, vetches, field peas and cold-tolerant clovers Select species capable of establishing and growing in low temperatures.
Arid or Low Rainfall Drought-tolerant crops selected for the season and available moisture Avoid using moisture required by the following cash or food crop.

How to Sow Green Manure

  1. Clear the growing area.
    Remove established weeds and excessive crop residue that may prevent seed from reaching the soil.
  2. Prepare the soil surface.
    Loosen and level the upper soil layer to create a fine, reasonably firm seedbed.
  3. Sow the seed evenly.
    Broadcast the seed across the area or sow it in rows using the recommended rate.
  4. Cover at the correct depth.
    Small seeds generally require shallower covering than larger legumes and cereal grains.
  5. Firm the soil gently.
    Press or roll the area to improve contact between the seed and moist soil.
  6. Water after sowing.
    Keep the seedbed consistently moist until the seedlings are established.
  7. Check establishment.
    Dense, even growth will provide better soil coverage and weed suppression.

Sowing rates vary considerably. Fine clover seed, large legumes, cereals and blended crops require different quantities per square metre or hectare. Follow the rate provided on the individual product page.

When to Cut Down Green Manure

Green manure is generally terminated before or around early flowering, while the growth is still soft and relatively easy to decompose. At this stage, the crop has produced useful biomass without forming mature seed.

Waiting until the plants become woody may slow decomposition. Allowing mature seed to form can also result in volunteer plants appearing in the following crop.

  • Cut with hand tools in small garden beds
  • Mow or slash larger areas
  • Roll or crimp the crop and retain it as surface mulch
  • Lightly incorporate the growth into the upper soil layer
  • Remove and compost the material where appropriate

Avoid deeply burying large quantities of fresh green material. Shallow incorporation generally provides better aeration and more even decomposition.

How Long Before Planting the Next Crop?

After cutting or incorporating green manure, allow time for the plant material to begin decomposing before planting the next crop. Approximately two to four weeks is a useful general guide, although the actual period will vary.

Faster Decomposition

  • Young, soft growth
  • Nitrogen-rich legumes
  • Warm and moist soil
  • Finely cut plant material
  • Shallow incorporation

Slower Decomposition

  • Mature or woody plants
  • High-carbon cereal growth
  • Cold or dry soil
  • Large quantities of biomass
  • Deeply buried material

Using Green Manure in Different Growing Systems

Vegetable Gardens

Use green manure between seasonal crops to keep beds covered, add organic matter and provide a productive break in the rotation.

Raised Garden Beds

Select crops that fit the available space and growing period. Terminate them before they become difficult to manage.

Orchards and Vineyards

Cover crops can protect inter-row soil, suppress weeds and provide habitat for beneficial insects. Consider water competition and mowing requirements.

Market Gardens and Farms

Green manure can form part of a crop rotation, fallow-management program or broader soil-restoration strategy.

Frequently Asked Questions

What is the best green manure crop?

There is no single best crop for every situation. The right choice depends on the season, climate, soil type and intended benefit. Legumes suit nitrogen fixation, grasses produce biomass and fibrous roots, while deep-rooted brassicas can help condition compacted soil.

Which green manure crops fix nitrogen?

Legumes such as clovers, vetches, field peas, cowpeas, lupins and medics can fix atmospheric nitrogen when compatible rhizobia bacteria are present. The correct inoculant may improve nodulation where the required bacteria are absent or limited.

Do I need to dig green manure into the soil?

No. Green manure can be lightly incorporated, left on the surface as mulch, rolled, crimped or removed for composting. The best method depends on the crop, available equipment and following planting.

Can green manure become a weed?

Any crop may self-seed when allowed to produce mature seed. Terminating green manure before seed formation substantially reduces this risk.

Does green manure replace fertiliser?

Green manure can improve nutrient cycling, nitrogen availability and organic matter, but it does not automatically correct every soil deficiency. Soil testing and balanced crop nutrition may still be required.

How long should green manure grow?

The growing period varies by species and season. Fast crops may be ready to terminate within several weeks, while winter cereals and legumes may remain in place for several months.

Can green manure improve clay soil?

Green manure can add organic matter and create root channels that improve aggregation, aeration and water movement. Deep-rooted crops and fibrous grasses are useful options, although severely compacted or poorly drained clay may require additional management.

What is a fast-growing green manure crop?

Buckwheat is commonly used as a fast warm-season cover crop. Millet and some other summer species can also establish rapidly under suitable conditions.

Can green manure be used in organic gardens?

Yes. Green manure is widely used in organic and low-input growing systems to increase organic matter, improve nutrient cycling and reduce the time that soil remains bare.

Packet and bulk quantities

Green Manure and Cover Crop Seeds for Australian Growers

Seedmart supplies green manure and cover crop seeds for home gardeners, market gardeners, commercial growers and larger soil-improvement projects.

Available pack sizes vary by variety, with bulk quantities offered across many products in the range. Check each product page for recommended sowing rates, seasonal suitability and growing requirements.