Cover Crops and Green Manure

 

We’ve all heard the phrase ‘cover crop’ at some point in our lives, we may have even vaguely understood the concept.  Most of us, however, have never heard of ‘green manure’.  In fact, most of us upon hearing the phrase vividly imagine a steaming pile of mutant green that we would rather have not pictured.  Some people think that they are one and the same, though they are not.  What they are, however, is of great benefit to any farmer or gardener and I’m here to explain why.

Cover crops and green manure crops share many of the same vegetation: various clover species, grasses such as barley and buckwheat, and virtually every member of the legume family (of which, strangely, clover is a member).  They both have the benefit of enriching the soil with their roots, prevent soil erosion, help retain water, and disallow weeds to grow because there’s no space to.  The fundamental difference between cover and green manure crops is this: the latter is tilled under while still green to further enrich the soil with it’s decomposition.  Essentially, you’re composting right there in the dirt, raising the nutritional value of the soil for years to come.

Be it that you have the worst soil on the planet or not, by growing a crop of ryegrass or clover you will improve it, and by tilling it under, the benefits are at least doubled–plus the loosening of the earth by tilling and root systems will make it vastly easier to dig into.  If the wagon is jumped on in early spring, a crop could be tilled under three times in a summer, effectively enriching your plain old backyard dirt into the envy of gardeners everywhere.

Where’s the downside?  Well, my dears, it’s time.  A single summer producing three enriching crops is fabulous, but the most productive growing season is sucked up by it, and no fruits or vegetables will be had until the following year.  Enriching can be a slower proccess, by utilizing the winter months for this variety of enrichment.  The winter months are typical unproductive, however by plating green manure crops in fall and letting them winter over, can be tilled in when spring arrives.  After two or three winters your soil will be as magnificent as a single overly-productive summer.

Cover crops are also used during the prime growing months to crowd out the seeding of weeds.  ‘Under-cropping’ corn with fava beans will save you hours of weeding through the spring and summer and yeild you beans for dinner more than a few times.  Planting clover between the rows of your carrots not only keep the weeds out, but rabbits prefer eating clover to carrots and will tackle the plants you don’t care about instead of the ones you do.

Even better?  Seed for cover and green manure crop are unbelievably cheap.  A two-pound bag of crimson clover goes for ten dollars at your local farm supply.  A two-pound bag of annual ryegrass only six.  A very small price to pay for improved, no-erosion soil and no weeds.

When the crop turned under in the spring, make it’s done roughly a month before you intend to plant anything.  The process of breaking down the green matter takes a lot of energy that your plants will have to compete with until it’s done, making it a risk for developing plants.

Typically all members of the legume family enrich the soil uniquely by taking nitrogen from the air and distributing it into the dirt, nitrogen is important (and often depleted by growth) for anything that wants to grow in the soil.  They also tend to grow deep roots, which naturally helps loosen the earth via their growth.  The drawback of legumes is that they often don’t have enough organic matter to enrich the soil that way.  Grasses add a lot of organic matter, but no exceptional nutrients like the legume family.  My personal opinion is that a mix of grasses and legumes are an optimum marriage for any space.

The following is a list of cover crops and their benefits as well as special needs, should there be any.

             

Type

Legume/
Nonlegume

Amount to Sow/
1,000 sq ft (oz)

When
to Sow

When to
Turn Under

Effects

Notes

Alfalfa
(Medicago sativa)

L

1/2

Spring/
Late Summer

Fall/Spring

Fixes 3-6 lb N/1000 sq ft/yr;
deep roots break up hard,
compacted soil.

Loam, fairly fertile soil; needs warm temperatures for germination; lime if pH is low; hardy; drought-tolerant; inoculate.

Barley
(Hordeum vulgare)

N

4

Fall/Spring

Spring/Fall

Adds organic matter,
improves soil structure.

Prefers medium-rich loam soil; lime if pH is low; not as hardy as rye; tolerates drought.

Buckwheat
(Fagopyron
esculentum)

N

2 1/2

Spring/
Summer

Summer/
Fall

Mellows soil;
rich in potassium.

Must leave part of garden in cover crop during growing season; grows quickly; not hardy.

Crimson clover
(Trifolium
incarnatum)

L

1/3

Spring/
Fall

Fall/Spring

Fixes 2-3 lb N/1000 sq ft/yr.

Not reliable hardy or drought-tolerant; lime if pH is low.

Fava beans
(Vicia faba)

L

Plant 8
inches apart

Early Spring/
Late Summer

Early summer/
Fall

Some types fix 1 1/2-2 lb
N/1000 sq ft in as little as 6
weeks. Use small-seed rather than large-seed table types.

Will grow on many soil types; medium drought tolerance; likes cool weather. Inoculate with bacteria as for other legumes.

Oats
(Avena sativa)

N

4

Spring/Fall

Summer/
Spring

Adds organic matter,
improves soil structure.

Not hardy; tolerates low pH.

Rye, annual
(Lolium
multiflorum)

N

3 1/2

Fall/Spring

Spring

Adds organic matter,
improves soil structure.

Very hardy; can plant until late fall/early winter.

Vetch, hairy
(Vicia vellosa)

L

2 1/2

Early Fall

Spring

Fixes 2 lb N/1000 sq ft/yr.

Slow to establish; fairly hardy; till under before it seeds; can become a weed; inoculate seed before planting.

Wheat, winter
(Triticum aestivum)

N

4

Fall

Spring

Adds organic matter,
improves soil structure.

Same as barley.

 

  Soybeans               

(Glycine Max)

 L  8 inches apart

Spring/

Summer

 Summer/               

    Fall

 Fixes Nitrogen  Treat as with Fava beans
White or Yellow Sweetclover              

(Melilotus alba and officinalis)

L As with other clover Anytime Anytime Fixes nitrogen  As with other clover

 

Other varieties that can be used but that I couldn’t find enough information on are Lupins, Rapeseed, Sudan Grass, and other legumes like peas and other beans.

 

This subject is neither a success or failure, the process is outlined below.

This subject is neither a success or failure as of yet, the process is being outlined below.

 

8-28-2008 :  Tilled most of my approximately 600 sq ft of ground with a self-propelled, rear-tined tiller (rented at 25 dollars an hour) for two and a half hours.  Soaked the overturned earth with water and spread a combination of 2 lbs crimson clover and 5 lbs ryegrass (all costing less than ten dollars) by hand in broad horizontal arcs. (I hope this is what they mean by ‘broadcasting’ the seed.)  It is much harder than one imagines to evenly disperse seed over such a large area.  I will try to keep the ground moist until established (hoping for rain).  There are pictures to come.

8-31-08 : It’s been four days, and despite some small birds often being caught eating the seeds at the very bottom of my yard, I have been persistent in keeping up with the watering with great rewards.  I was so delighted the day after tilling when I discovered that all of the tiny clover seeds had matching tiny white threads trailing from them.  Now on day four there are tiny, adorable green leaves poking their heads out to see the world and the rye seeds have threads in the ground.  I feel like a proud mama.

9-6-08 : It’s been another week and my clover leaves are bigger and the rye is over two inches tall.  When the latter first sprouted they were a dark red color and now they are a vibrant spring green.  I have not had to water them the last four days with no signs of ill effects and hardly any rain.  I still can’t help but smile when I look out at them.

 

 

Sources:

Jackie French

Suite101

The Encyclopedia of Country LIving

COGS

Garden Guides

Mother Earth News

Clemson Extension

Image courtesy of Rodale Institute

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2 Comments

  1. September 2, 2008 at 4:53 am

    Do you think I could possibly use this method to improve the soil in my raised beds? I really could use to improve the soil in one especially. Hmmmmmm. I just may have to consider it.

  2. Sinfonian said,

    February 20, 2009 at 7:42 am

    May May, sure you can. My brother did it last year with great success. Good luck with it! Brandy, I love that you cultivated 600 SF and amended it with a cover crop! You will be very happy with the results I expect! Great blog. You like researching even more than I do. Bravo!


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