Green Manure Crops

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PHOTO: MOTHER EARTH NEWS STAFF
After only two years of green manure cropping, Ecology Action's gardens were transformed from barren ground to the verdancy shown here.

Garden magic from John Jeavons and Bill Bruneau.

Green manuring — growing green manure crops especially for their
organic matter and ability to improve the soil — can
dramatically build up poor and exhausted soils and maintain
the fertility of better ones. Let me give you two examples
from our own experience. When we first started Ecology
Action of the Mid-peninsula in 1974, we were minifarming a
site in the Stanford Industrial Park that had no
topsoil or subsoil: It had all been scraped off in
anticipation of future construction. Eight years later, we
had improved the soil by using green manure crops to a depth of over two feet!

Then in 1982, we moved to our current steep hillside
location in northern California. Its thin rocky topsoil had
few available nutrients. Indeed, some feel the site
approximated marginal Third World growing conditions. But
now, four years later, it is becoming a beautiful and
productive garden/minifarm.

In both cases, we were able to dramatically improve the
soil through deep cultivation, intensive plant spacing, the
addition of composts and aged manures . . . and a
continuous program of growing green manure crops.

Growing Green Manure Crops

Green manuring will help your soil in many ways. Perhaps
most important, it boosts your plot’s organic matter (O.M.)
level. And a high O.M. level (2.5 to 4%)

— keeps nutrients from leaching down beyond reach of
crops,

— provides food for microbial soil life,

— helps legumes fix nitrogen in their root nodules,

— and helps the soil produce good structure and
maintain the air-pore spaces essential to good crop health.

In addition, your green manure crops will till the
soil
for you. Alfalfa, for instance, can send down
roots as deep as 60 feet, pulling up nutrients for next
year’s crops. A single rye plant grown in good soil can
produce an average of three miles of roots per day —
387 miles of roots and 6,603 miles of root hairs in a
season! Such root and roothair growth will
fiberize the soil, helping loose soils bind
together and clay ones open up.

Green manures also provide a living mulch that
will protect soil from erosion and other weathering
effects. Indeed, right now, during the late summer and
early fall, is an excellent time to put in a green manure
crop. The plants will protect your garden from winter
damage and will produce organic matter during the
off-season, when much of. your plot would otherwise lie
fallow. Then next spring, your soil will have good tilth
instead of being hard and compacted.

Many fall-planted green manure crops will also pump
excess water
out of the soil, allowing you to prepare
the soil and plant crops much earlier than usual. Fava
beans, for instance, can pump soil dry in as little as five
days of warm weather. (If, on the other hand, you are
trying to conserve soil moisture in early spring, you may
want to harvest your green manure crop on the first warm
day.)

Compost It

To get the maximum benefit from a green manure crop, you
should compost it. If, instead, you spade or till it
directly into the soil, you’ll have to wait 30 days for it
to decompose before you can plant again. (Turning under
such a crop is also quite arduous.)

You’ll do far better if you compost the current green
manure crop, while using compost made from the
previous growing season’s green manure (along with
kitchen and other garden waste) to fertilize the current
planting. You can harvest the crop by pulling it out by
hand or skimming it off with a sharpened spade.
[EDITOR’S NOTE: See “Skimming the Garden” in MOTHER EARTH NEWS NO.
99, page 72, for a complete explanation of this
technique.]
In our experience, a one-inch layer of
cured compost — about eight cubic feet per 100 square
feet — appears to maintain fertile soil in good
health. (Other organic fertilizers may be needed to
initially build up a soil’s nutrient reserve . . . or even
to maintain that level if not all waste nutrients
are returned to the soil.)

We feel the secret to composting green manures
successfully is to combine lots of fresh green matter (from
a legume crop, when possible) with lots of dry carbonaceous
matter and one-third topsoil (by weight). The
green matter — from your freshly cut manure crop
— provides nitrogen to the pile. The dry matter
— from a previously cut manure crop, or other dry
material such as leaves and straw — provides the
carbon that holds the water-soluble nitrogen in
the compost (and, later, in the soil). And the topsoil
slows and cools the composting process. There are
indications that slow-cooked compost will produce 12-40%
more compost (excluding the soil itself from these
percentages) than hot-cooked piles. Hotter piles, in
effect, burn off part of their mass.

Four Old Crop Standbys

Below are some good green manure crops you might think
about growing. When choosing one green manure over another,
consider

— how much O.M. it will add to the soil,

— how much nitrogen it will return to the soil (many
soils need up to .5 pound of nitrogen per 100 square feet
per year),

— if it can pull up nutrients from the substrate
below,

— if the crop fits your particular soil and weather
conditions,

— and if you want the harvest to also provide food
for your family.

Remember that two or more green manure crops can often be
grown together to their mutual benefit, and that you can
frequently save seed from your current crops so you can
reseed for free next year.

The first four crops we’ll list are old standbys; ones that
have served often and well.

Cereal rye produces lots of organic matter
(the rye straw grows up to seven feet high) and
lots of roots (which makes it very good for fiberizing
compacted soil). It’s also drought-tolerant and very
winter-hardy . . . and, of course, can give you food: rye
grain.

Sow this rye in cool weather — in many areas, you can
plant it in fall and expect it to overwinter and produce
abundantly the next spring. It matures in as little as 16
to 18 weeks of growing season. If you want to harvest the
grain, time your planting so the rye will have only about
one month of hot weather before it matures. Yields are up
to 60 pounds of rye straw per 100 square feet plus 4 to 26
pounds of grain.

Agricultural mustard is a very
fast way to get lots of green matter: It can
mature in as little as six weeks and yield 180 to 270
pounds of green matter per 100 square feet!

Other benefits are that agricultural mustard will grow in
cold or hot weather and that it apparently has the ability
to bring health back to rundown soil. It’s often used in
orchards to reclaim and “invigorate” land. It also attracts
honeybees.

You can harvest this O.M. crop at any growing stage, but
just after flowering is best.

Alfalfa can be grown for just one growing
season, but this perennial is better used for long-term
soil buildup . . . say, in an area you plan to start
cultivating in a year or two. A deep-rooting crop, it
boosts fertility by pulling nutrients up from subsoil. And
since it’s a legume, its roots fix nitrogen in the soil:
from .36 to .57 pounds per 100 square feet per year.

Drought-tolerant alfalfa thrives in all growing seasons,
maturing in about 17 weeks (although it can take a while to
get a stand established). You can harvest ituse it for
green matter, not dry — repeatedly through the
season. Traditionally, farmers cut their alfalfa at
nine-week intervals, but the best times are when about 10%
of the plants are in bloom; those can be anytime from three
to twelve weeks apart depending on climate and season.
Alfalfa can provide from three to six cuttings a year and
from 80 to 360 pounds and more of green matter.

When you want to clear the land for other crops, you’ll
have to dig the roots out — a job hard enough to keep
you in shape without jogging. (If you clear the crop out
when it’s just three months old, you won’t have to dig the
roots out, but can let them decompose in the ground.)

Banner fava beans are quite hardy legumes
that are very good for spring growing. If your winters
don’t drop below 10 degrees Fahrenheit, a fall planting will keep
growing throughout the cold months. The plant grows from
four to six feet high, produces lots of green O.M., and, as
noted earlier, can bring up excess moisture from damp
spring ground. It also tolerates acidic soil conditions.
When we minifarmed in mildclimate Stanford, fava beans made
our garden productive year-round and were our favorite
green manure crop.

Banner favas mature in 11 to 26 weeks. They fix .16 pounds
or more of nitrogen per 100 square feet per season, and can
yield 90 to 360 pounds of green matter. They also can yield
5 to 18 pounds of dry beans. Many people enjoy eating fava
beans — they are a staple in Egypt — but a few
people are fatally allergic to them.

The next four crops we’ll discuss are some unusual,
specialty , ones you might consider growing.

Specialty Crops

Alsike clover is the “poor soil
workhorse.” It grows in any temperature except severe cold
… tolerates depleted, acidic, and poorly drained ground .
. . and stands up well to drought. The legume produces an
adequate (not large) amount of green matter and nitrogen
(about .27 pounds of N per 100 square feet). Sow it in
spring or autumn for best results.

Fodder radish has a deep taproot for
bringing up nutrients from the subsoil and produces more
organic matter per day than almost any other green manure
crop. Although you can use it for green matter, it will
also produce a great deal of carbonaceous dry matter if you
let it grow for several months until the plants are
“woody.”

Fodder radish grows well in hot or cool weather, but it’s
best sown in late summer, early autumn, or early spring. It
will mature in as little as 17 weeks and can yield 100 to
500 pounds of green matter per 100 square feet.

Wooly pod vetch , like alsike clover, is
good at growing in poor soil and under conditions such as
heat or drought. In addition, it’s very hardy
— it can handle cold down to 0 degrees Fahrenheit! (It’s more
cold-tolerant, but less productive, than its cousins purple
and hairy vetch.) It can also help knock out weeds in a
garden by outcompeting them.

A medium-fast-growing legume, wooly pod vetch produces only
an adequate amount of green matter (about 50 to 200 pounds
per 100 square feet) and nitrogen (up to .25 pounds). It
matures in 12 weeks and can be harvested more than once at
approximately nine week intervals.

Foul muddammas beans grow well in heat, so
they’re suitable for late spring and summer sowing. They
also have a good root system which can fix up to 16 or more
pounds of nitrogen per 100 square feet.

Foul muddammas mature in 11 to 26 weeks, depending on
season, and yield 45 to 180 pounds of green matter per 100
square feet and 5 to 30 pounds of beans.

The last green manure crops we’ll mention have an extra
“by-product”: They can be harvested for food as well as for
dry carbonaceous organic matter.

A fall green manure crop gives off-season
garden productivity!

Double-Duty Crops

Drought-tolerant hard red spring wheat
should be planted early so it will mature after only about
one month of hot weather. (Its growing season is from 16 to
18 weeks.) It produces a lot of straw for dry O.M.: 20 to
60 pounds per 100 square feet.

The grain yield is 4 to 26 pounds per 100 square feet (the
average American consumes about 110 pounds of wheat per
year).

Like spring wheat, barley should be
planted to mature after only one month of hot weather. But
barley has a much shorter growing season — from 9 to
10 weeks! — so you can sneak it in a spot you can
spare for only two to three months. It actually contains
somewhat less protein and calcium per pound than wheat or
oats, but — due to its shorter growing season —
produces more of these nutrients per day of growing time.

Barley is a good straw producer (up to 60 pounds per 100
square feet) and yields 5 to 24 pounds of grain (the
average American consumes only about 1.2 pounds of barley
each year).

Grow your own oatmeal! Cold-hardy oats
mature in 13 to 17 weeks, and like barley and spring wheat,
need about one month of hot weather near harvest.

One hundred square feet will yield up to 60 pounds of oat
straw and 4 to 17 pounds of oats (the average American
consumes about 3.2 pounds of oats each year).

There are many other good green manure crops. [EDITOR’S
NOTE: The ones we’ve used most often at MOTHER ‘s
Eco-Village have been winter rye mixed with hairy vetch for
fall-to-spring plantings . . . and buckwheat for
short-term, warm-season growing.]
Any of them will
help you build a living soil from which you can harvest
increased crop yields.

Building your own soil is important for broader reasons, as
well. When we use fertilizers and organic matter from
somewhere else for our gardens, we may actually be
depleting the soil resource base of another growing area.
By improving our own soil base with “homegrown” materials,
we’re taking a small step toward improving our whole
planet’s soil and life resources.

In fact, in a world of diminishing agricultural
petrochemical resources, green manure is as precious as
gold. From 1975 to the year 2000, it is expected that the
percentage of desert on the earth’s land surface will
increase from 49% to 63% or more — and one-third of
this process is expected to occur in the United States!
Each backyard garden or homestead can contribute to our
planet’s much-needed increase in soil fertility.


Sowing Green Manure Crops

Almost all of the green manure crops mentioned in this
article can be directly sown into prepared soil by
hand-broadcasting. When doing so, under broadcast
at first, so you’ll have some seed left to fill in any
gaps. Then gently chop the seed into the soil by poking
holes in the area with a rake. You may also want to tamp
the soil down with a wide board to eliminate excess air
spaces. Finally, water the area thoroughly.

Some of the crops will produce more, and more quickly if
you first sprout them in soil on 1 inch centers in growing
flats. After 5 to 10 days, when the seedlings are about
1-1/2 inches to 2 inches tall, transplant them into the garden. This
works well with cereal rye, alfalfa, hard red spring wheat,
barley, and oats — all of which set out on 5 inch
centers.

Banner fava bean seed should be directly planted on 7 inch
centers, and foul muddammas fava beans should be directly
planted on 6 inch centers.


EDITOR’S NOTE: Ecology Action sells seed for all of the
above-mentioned green manure crops, in allotments big
enough to cover 100 square feet. Alsike clover, fodder
radish, and agricultural mustard cost 80 cents each per
allotment . . . barley and oats cost 90 cents each . . .
cereal rye, alfalfa, and hard red spring wheat cost $1 each
. . . wooly pod vetch costs $2.50 for one allotment, $3.50
for two, and $5 for three . . . banner fava beans cost $4,
$7, and $10 for one, two, and three allotments . . . and
foul muddammas fava beans cost $4, $6.50, and $9.50 for
one, two, and three allotments. (Jeavons suggests you
reduce your fava bean cost by buying just one unit and
saving your own seed for later plantings.) All prices are
postpaid from Ecology Action,Willits, CA.

John Jeavons was the subject of THE MOTHER EARTH NEWS feature
interview in issue 63, in which he explained how his
biointensive (also called biodynamic/French intensive)
growing techniques could help combat world hunger. He is
the author of one of our all-time favorite gardening
books,
How to Grow More Vegetables ($10.50).

Jeavons’ nonprofit small-scale food research group also
publishes
The Backyard Homestead, Mini-Farm &
Garden Log Book ($10.50) for those who want to become
more effective food growers . . .
One Circle
($9.50), by David Duhon and Cindy Gebhart, a guide to
producing a complete year’s diet in as little as 1,000
square feet . . .and
Growing to Seed ($3.75), a
70-page booklet on seed saving. Again, all prices are
postpaid from Ecology Action.