Prepare Your Garden Soil:
Growing Edible Cover Crops
Cover crops or green manure crops are exceptionally vigorous plants that are grown primarily to improve soil. They are usually the cheapest and most ecologically sound way for farmers and gardeners to improve and maintain the fertility of their soil.
Cover crops protect and improve soil in different ways. They all capture carbon dioxide from the air, where it is driving climate change, and put it into the soil as beneficial organic matter. As much as a third of the carbon that plants capture from the air is extruded directly into the soil through their roots as sugary compounds that feed the soil life.
Atmospheric carbon is also captured as organ ic matter in the roots, stems, and leaves of the cover crops. Soil bacteria and fungi feast on all this organic matter. Protozoans then feast on the bacteria and excrete the excess nitrogen in plant friendly forms. To give a sense of the scale of all this feasting; there can be millions of protozoans in a teaspoon of soil and each one can eat up to 10,000 bacteria a day. (Who does this counting?)
Beyond capturing carbon, cover crops in the legume (or pea) family have an additional and extremely valuable ability.
In cooperation with rhizobia bacteria that form nodules on their roots, legumes can capture nitrogen from the air and convert it into forms that plants can make use of.
Cover crops with powerful taproots, like turnips and radishes, can punch into hard subsoil, allowing the roots of crops that follow to grow deeper.
Cover crops in the grass family form dense mats of roots near the soil surface. As these die they feed beneficial bacteria and fungi and leave millions of little passageways for air and water to move through the soil. Almost all cover crops are essentially leaf crops, in that they work best when the plants are cut down before flowering or forming seeds. Many of the most effective green manure crops have inedible or even toxic leaves. This group includes buckwheat, velvet bean, sword and jack bean, fish bean, and sunn hemp.
However, there are many other good cover crops that have leaves that are edible and can serve as leafy green vegetables. Generally, you can harvest up to about 1/3 of the leaves of these edible cover crops to eat as vegetables while still retaining much of their soil improving capacity.
When you harvest 1/3 of the leaves for your kitchen; the remaining 2/3 of the leaves, plus all of the stems, plus all of the roots, plus the liquid carbon extruded through the roots still go into the soil. This strategy simultaneously addresses two serious food system problems; declining soil fertility and the lack of vegetables –especially leafy green vegetables- in our modern diet.
The potential of this strategy is greatest for low-income smallholders and subsistence farmers.
While they are often aware that cover crops could improve the fertility of their soil, their economic circumstances may be too precarious for them to take any land out of food production while the cover crops rejuvenate their soil.
Eventually, choosing food production over soil health leads to declining fertility and even worse economic circumstances. The grower might be able to bypass this “either /or” quandary by using part of her cover crop to improve the family’s diet and health.
An enterprising grower might find ways to sell some of these leafy greens. (The LFL website has suggestions for making a variety of leaf enriched foods; some of which could be marketed)
The most important criteria for choosing edible cover crops are:
- that they can improve the health of your soil
- and that they taste good enough to be eaten regularly.
Our favorite plant for an edible cover crop is the cowpea.
Black-eyed peas are the best known variety of this warm weather plant. Cowpea leaves are widely marketed as a vegetable in parts of Africa and Asia. As a leafy vegetable they offer lots of nutrition and a mild flavor. As a cover crop they grow quickly even in poor soil and with little rainfall and produce a lot of bio-mass, or organic matter.
These nodules on the cowpea roots are colonies of rhizobia bacteria that can capture a lot of nitrogen from the air for crops that follow.
A garden bed of 100 square foot can produce about 60 pounds of cowpea plants per season. About 40% of the plant is leaf, 40% is stem and 20% is root. If you harvest 1/3 of the leaves, roughly 52 pounds of plant still goes to the soil.
Cowpeas are also an excellent green manure intercrop, planted between rows of taller plants like corn and cassava. Or in this case between rows of tomatoes. Intercrops don’t always look tidy, but they have a long history of improved production.
And if you should happen to let some flower and go to seed you have high protein peas for Hoppin’ John and other dishes and seeds for the next crop.
Our second place cover crop is Austrian winter peas. They are a cool weather legume that makes a thick tangle of vines. The leaves have a delicate and delicious pea flavor. Where cold weather prevents gardening over the winter, these peas are an ideal way to prepare your soil for spring while getting a bonus vegetable crop.
When they begin to make their beautiful two-tone purple flowers, we usually cut them as close to the ground as possible and leave them to rot in place. This is sometimes called “chop and drop.” You can cut them with a sickle or a scythe or a weed whacker.
Two or three weeks later we punch holes in this layer of mulch and plant seedlings.
This works much better with small plants, like this tomato, rather than with seeds, that can get lost in the mulch.
Barley and wheat are two other favorite edible cover crops. Both are cool weather crops, but neither fixes nitrogen. Instead they produce a lot of bio-mass and leave behind a dense mat of roots. Although they are well-known as grains, the young leaves of both barley and wheat are eaten. Wheat grass juice and barley leaf powder have long been available through health food stores. I am not a big fan of wheat grass juice, but find barley leaf powder to have a very pleasant flavor.
These grasses can be very stringy, but if you cut them before the flower, then blend them into smoothies or dry and grind to a powder they are easy to incorporate into many different recipes.
Or you can simply sprinkle the dried leaf powder over rice or popcorn for extra vitamins and minerals.
You can accelerate the soil improvement by planting barley and wheat in close rows with 2 inches of compost placed between them.
Other cover crops whose leaves can be eaten include fenugreek (a popular leafy vegetable in India), hyacinth bean, rice bean, scarlet runner bean, and butterfly pea. These are all good nitrogen fixing legumes. Other than fenugreek, the flavor of these leaves is not as good as that of cowpeas or winter peas, in my opinion.
Among non-legume edible cover crops are turnips and mustard, whose greens are well-known vegetables.
Forage radish, rape (or Canola), and sugar beets are other non-legume cover crops that can be eaten.
So far all of the cover crops mentioned have been grown as annuals, that need to be replanted each year.
A couple of perennial plants that can be used as edible cover are pigeon peas and moringa. Pigeon pea is a beautiful plant that fixes nitrogen and can be cut back many times. Unfortunately, while they are edible, pigeon pea leaves are not tasty.
Moringa, on the other hand, can’t fix nitrogen but the leaves are used as a vegetable in much of the tropics, and lately as a health food in the US and Europe. Moringa is an incredibly productive and fast growing tropical tree from India. In frost free climates it grows year round for many years without replanting. And moringa leaves have enough protein, vitamins, minerals, and antioxidants to put them near the very top of any nutrition chart.
There are a lot of different schemes for growing moringa. It produces the most leaves when grown close together and harvested several times a year.
We use a coppice system, cutting the trees down to less than knee height, two or three times a year.
We usually then strip most of the leaves and small branches from the moringa and then carry them off to use either as a high value mulch or to heat up our compost piles. This is called a “cut and carry” system.
Of course, we always set some aside for using in soup and drying to make green pasta.
There is good information on-line and from agricultural extension services which cover crops or green manure to grow and how to grow them. Choosing ones that also produce edible leaves can expand your possibilities.
Both your body and all your garden crops will benefit.
Thanks for watching.
View this video on YouTube (and subscribe to our channel at Leaf for Life @ YouTube)