Grow green manure

It’s important not to leave your garden soil bare. Instead grow a green manure to improve soil condition. Use either the physical space between crops e.g. undersowing medicago; or use empty space post harvest/flowering & before the next crops/flowers e.g. Vicia overwintering. Details in table below.

The adverse effects on soil of leaving it bare

Rye & Field Beans growing as a 'Green Manure'

Rye grass & Field Beans to overwinter.
U.K. gardeners may find the seeds on this link
  • Soil particles exposed to rain impact can break down.
  • Soil pores become blocked.
  • With no plant roots growing, drainage channels will be lost.
  • Poor soil structure leads to poor aeration, surface runoff, soil erosion. Increased percolation through soil mass instead of through drainage channels causes more leaching.
  • Leaching washes nutrients from the soil.
  • Beneficial soil microorganisms will not flourish.
  • Earthworms have less organic matter to sustain them and less protection.
  • Light stimulates germination to some extent. An open cultivated soil is easily populated by weeds.
  • No root competition means stronger weeds and more weed seeds.

The Green Solution – not a bottle of fertilizer but -
a packet of seeds.



U.S.A. Seeds.

Here's how a growing green manure plants can help.

  • The shade of dense foliage will reduce weed seed germination. Mulch also does this but better still plant roots can also inhibit the growth of weed competitors.
  • Beneficial soil microorganisms flourish.
  • Plants absorbs available nutrients that would have been of leached out of the soil. They can now be recycled in organic form to be made available when the plants are dug in or composted.
  • Plants of the Pea/Bean family often have root nodules populated by bacteria that convert nitrogen from air into useful organic nitrogen. Other plants, such as Rye or Buckwheat, use an extensive root system to absorb and concentrate nutrients like potassium that may otherwise be unavailable to crops.
  • Living roots feed microbes and produce colloides that increase the water holding capacity of soil to make it more drought resistant.
  • Living roots may improve the stability of soil particles and create useful drainage channels.
Green manures are chosen so they won’t give you a weed problem. But they will keep weeds down and improve soil condition and nutrition.

A green manure is commonly sown immediately after one crop finishes but before the next crop. Some can be under sown or fitted in between rows e.g. nitrogen fixing medicago around leafy cabbage.

Green manures may be cut down and dug in, or in a no dig system, cut and left to lie or composted. Cut when young - before they become woody and before flowering. At this stage the nitrogen content is relatively high. Some nitrogen fixers may be left for more than a year because their root nodules add nitrogen and there’s improvement over time.

**Caution: – some green manure plants e.g. Secale cereal and Vicia sativa will release germination inhibitors when dug into the soil. That’s great for weed prevention but it also means that sowing small seeded crops has to be delayed by about 1 month after digging in.

Don’t forget to rotate green manures as you would any other crop. E.G. rotate Vicia, and Alfalfa, with Peas/Beans, Mustard and Fodder Raddish with Brassicas. Click here for more reading.

Green manure can also attract wildlife providing cover and food for predators like frogs, and hoverflies, and pollinators like bees. You may decide for example to leave some of your Alfalfa, or Phacalia, to flower. Read more on companion plants.

How Green Manures Are Used.


Sinapsis alba
Sow spring - autumn – between crops.
Dig in when young.Best in moist fertile soils Rotate as with Brassicas. Not for soils with clubroot.

Fodder Radish
Sow summer
Rots down for good winter cover.Any soilRotate as with Brassicas. Not for soils with clubroot.

Fagopyrum esculentum
Sow spring & summer
Dig in before seed set. Tolerates poor soilDeep roots compete with weeds. Source of calcium. Pretty flowers attract hoverflies.

Secale cereale
Sow late summer to autumn
Fast ground cover. Fibrous roots improve top soil. Hard to dig in – dig in 1 month before sowing**.

Medicago sativa
Sow from April – July grow for several years.
Several cuts a year, for mulch. Deep roots, concentrate minerals, fixes nitrogen if Rhizobium bacteria present. Attractive flowers.

Trifolium incarnatum
Sow March – August, grows 2-3 months
Can over winter. Best on lighter soilsFixes nitrogen, flowers attract bees.

Trifolium pratense
Sow March – August
Cut before floweringNot for poor or moderately acid soils.Fixes nitrogen. Best left for a year or more.

Alsike Clover
Trifolium hybridum
Sow March – August
Cut before floweringMore acid tolerant, avoid very dry soil. Fixes nitrogen.

Medicago lupulina
Sow August to overwinter dig before seed set, or sow from March.
Shade tolerant, use for undersowing Grows in dry soils, avoids acid soilFixes nitrogen.

Winter Tare
Vicia sativa
Sow in spring or mid-summer - autumn to overwinter
Rotate with peas/beans – leaves readily available nitrogen for leafy crop e.g. brassicas For heavy soils, avoids acid soil dry soils Fixes nitrogen. dig in 1 month before sowing**.

Phacelia tanacetifolia
Sow in spring or mid-summer - autumn to overwinter.
Needs shelter to overwinter, good choice for winter greenhouse. Most soils. Attactive flowers good for bees, hoverflys…

grow from root cuttings or offsets.
For permanent bed.
Cut about 5 times a year. Make fertilizer, mulch, compost activator and more...Most soils Deep roots concentrate potassium. Find more on Comfrey here.

My local garden centres and most online stores no longer stock Green Manure seeds but see the links below.

BOTTOM OF THE GARDEN - more information and links

Green Manure/cover Crop Systems Of Smallholder Farmers: Experiences From Tropical And Subtropical Regions.

book cover

Compost, comfrey and green manure report from the H.D.R.A.


  • SUTTONS SEEDS - now stocking green manure seeds plus handy seed tapes & seed pads to simplify sowing of some seeds
  • The Organic Catalogue - a good selection of green manure seeds here



^ Top of page

<< Go to Grow Compost Go to Organic Fertilizer >>

Share this page:
Enjoy this page? Please pay it forward. Here's how...

Would you prefer to share this page with others by linking to it?

  1. Click on the HTML link code below.
  2. Copy and paste it, adding a note of your own, into your blog, a Web page, forums, a blog comment, your Facebook account, or anywhere that someone would find this page valuable.