Planting green manure crops for small farms can transform farm soil fertility in a short time. Learn to composting method, four standby green manure crops, and double-duty crop suggestions.
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 or mini farm.
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 for Small Farms
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. [See “Skimming the Garden” in MOTHER EARTH NEWS NO. 99, page 72, for a complete explanation of this technique.] In our experience, a 1-inch layer of cured compost — about 8 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% to 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
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.
Mustard
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
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 0.36 to 0.57 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 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 12 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
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 mini-farmed in mild-climate 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 0.16 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.
Specialty Crops
The next four crops we’ll discuss are some unusual, specialty , ones you might consider growing.
Alsike Clover
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
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
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
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.
Double-Duty Crops
Hard Red Spring Wheat
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).
Barley
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).
Oats
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.
Resources
- Jeavons’ nonprofit small-scale food research group also publishes The Backyard Homestead, Mini-Farm & Garden Log Book for those who want to become more effective food growers
- One Circle by David Duhon and Cindy Gebhart, a guide to producing a complete year’s diet in as little as 1,000 square feet
- Growing to Seed, a 70-page booklet on seed saving
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.
