Grow Edamame

Winter 2003-2004

Butterbeans, a cultivar of edible green vegetable soybeans, have a sweet, buttery flavor. Photo courtesy of Johnny’s Selected Seeds, Albion, Maine.

By Roberta Bailey

Nearly 20 years ago, I wrote an article for The MOF&G entitled, “What is tofu?” At the time tofu was not available in convenient, pre-packed cartons on any grocery store shelf, but could be found in a 5-gallon pail in the cooler of the local food co-op, or you could make your own. Francis Moore Lappe’s message of a vegetarian “Diet for a Small Planet” was just taking hold. Many of us were learning to pass up the beef and cook with rice and beans, tofu, tempeh and miso. But very few were using edamame.

What is edamame? Edamame is an Americanization of eda mame, one of the Japanese words for soybeans that are grown until they are filled out in the pod, but still green. The soybeans are shelled and eaten as a sweet, nutty snack or as a protein-rich part of a meal. They have become a popular bar snack called beer nuts. I find them to be delicious plain, with rice, in soups or used in place of lima beans.

Eda mame, or wild soybeans (Glycine max), originated in eastern Asia. They are called daizu in Japanese, da dou in Mandarin (a general term for soybean) and Tai tau in Cantonese. The Chinese have cultivated them for close to 5000 years, over time developing a wide range of uses. With close to 20 percent oil content, soy oil fueled lamps and stoves. With nearly 40 percent protein and lacking only one amino acid for complete protein, soy became an important part of the diet. The use of soy in the diet throughout Asia was probably hastened by the vegetarian doctrine of Buddhism.

The soybean was not known in Europe until the 17th century, and the Americas paid little attention to it until the early 1900s, when its high oil content garnered interest. Soy oil began to be used industrially in soap, paint, varnishes, and later, plastics. Because soy oil is highly unstable, subject to oxidation and to absorbing off flavors, it was not used for food until the invention of hydrogenation. During W.W.II, soy margarine replaced butter. The soybean’s high protein content, two to four times that of beans and corn respectively, made soy an attractive stock feed. Today, soy is the single largest cash crop in the United States.

In recent years, much of that crop has been genetically engineered, providing incentive for GMO-wary farmers and gardeners to grow our own. I have tried organic frozen green soybeans; they lack the sweetness of homegrown edamame.

Soybeans, an annual crop, are cultivated much like bush green beans. The erect plants stand 12 to 30 inches tall, with some varieties reaching 5 feet. A downy fuzz covers the three-leafed leaflets, stems and pods. Small white to lilac blossoms give way to 1-1/2- to 3-inch pods that are about 1/2-inch wide. Plants bear dozens of the pods, each with two to four beans.

The seed is green, black, yellow or creamy white. Green seeded varieties are the most tender and best flavored and are more widely adapted for the north.

Black seeded varieties are thin-skinned, tastier and easier to cook than yellow, though most are difficult to mature in the north. Among other things, they are used for black bean sauce.

Yellow seeded soybeans are used primarily for soy milk, flour, bean curd, tempeh, tamari and sprouting.

Dried beans are very hard and need to be soaked overnight (or for at least five hours), with two water changes before boiling.

Because soy can be hard to digest, it is often cultured or fermented (as in tempeh, tofu, miso and tamari) before being used in Asian culture. Edamame are easy to digest, as are sprouted soybeans. (Sprouts and edamame are about 16 percent protein versus 40 percent for dry beans.)

Soybeans mature in 75 to 110 days. They are daylength sensitive. Originally, varieties needed the long days of early summer to flower, but many varieties have been developed for northern latitudes. Most require three to four months to mature seed.

Field soybeans are used for green manure crops, hay, silage and feed seed. Many of the field varieties have been selected for lush growth and may be longer season plants with more of a sprawling habit.

Folk opinion says to plant soybeans when the apple trees are in full bloom or their petals are dropping. The seed germinates best between 60 and 80 degrees F. Set the seed 1/2 to 1 inch deep, spaced six to 10 per foot, in rows 15 to 30 inches apart. Thin to 3 to 4 inches between plants.

Inoculate the seed with specific soybean inoculant for better nitrogen fixation and higher yields. Plants will do quite well, however, if inoculant is not available.

Soybeans and corn often follow each other in crop rotations, but Will Bonsall and Molly Thorkildsen of Khadighar in Industry, Maine, plant edamame with their sweet corn. As Will says, “You go out and pick a few ears and grab a few handfuls of pods as well.” The dry, yellow soybeans grown with their field corn are all harvested at once. Will notes that the soybean yields are lower due to some shading, but the overall yield of both crops per row foot in the corn patch is higher when adding the soybeans, a good use of limited space.

Soybeans prefer a pH of 6 to 7, and they thrive in full sun and humus-rich soil with reasonable drainage. Avoid nitrogen-rich ground. If a soil test recommends adding fertilizer or soil amendments, note that inoculated soybeans need more phosphorus and potassium than nitrogen.

Once soybeans are up and thinned, you may need to protect your plants from pests. Although Mexican bean beetles do not bother soybean plants, rabbits, deer and woodchucks find the plants delectable. Row cover, electric fence or live traps are among the best solutions. When my plantings are more remote than my dog’s regular patrol areas, I use polyspun row covers; these covered plants have escaped the attention of deer and woodchucks. Regarding weed control, cultivation is easy around the erect plants.

The plants bloom in midsummer, then form pods that swell over the next month or so. Harvest green soybeans when the beans in the pods are filled out; when you can feel a good-sized bean inside the pod. Open a few to see how they are sizing up. The pods will still be green or just barely starting to fade to yellow. Once the pods turn yellow, the seed inside starts to lose its sweetness and becomes starchy, then dry and hard. The harvest period is seven to 10 days long. Some plants seem to ripen almost all of their seed at once, although I have seen a few varieties that have a more staggered ripening. Plan on two full pickings with a third to catch the stragglers as an option.

Once picked, the beans lose their quality quickly, so process them within a few hours of picking. For this reason, some market gardeners have started selling bundles of soy plants with the pods intact but stripped of their leaves, making the beans last much longer and producing less labor for the harvester.

Soybeans are very difficult to shell unless you blanch them in boiling water or steam them for five minutes. Cool the lot in icy or cold water, then shell and pack them for freezing. Some people save time by freezing the blanched soybeans, then shelling them when they take them from the freezer. I employ a good friend, a good video, or a good reader and commit to a few hours of work at harvest time. I know I am more apt to use the soybeans in the winter if they are already shelled.

Because I grow a lot of soybeans (these things are really delicious), I stagger my plantings by one week: I don’t trust that varieties said to mature one week later will actually do that. This year I had a trial of 10 varieties, and they all matured at the same time. Fortunately my main crop matured a week later.

Saving your own soybeans for seed is very easy, since soybean flowers are self-fertile. The anthers dehisce (shed pollen) before the flowers open, eliminating the possibility of varieties cross pollinating. Your seed will grow true to type next year. The easiest way to harvest seed is to gather the seed that goes by after your edamame pickings – but this method increases your risk of picking small or weaker seed. The optimal method is to mark a small section of a row and save all of that seed, ensuring fat, well-matured seed for your future seed stock.

Harvest plants for dry seed when the leaves are yellowed and the stalks are still green. Leaves will drop if they are frosted, but if the pods are fairly dry, no damage will be done. Hang the plants to dry fully in an airy shed, garage or barn. For small plantings, the pods can be picked once they are dry and can then finish drying in a well-ventilated place.

Yield reports vary greatly. Northern varieties will yield 1 to 3 pounds of dry seed per 10-foot row.

As soybeans become more popular, seed companies are offering a few varieties. Look to catalogs that cater to your growing season for regional varieties. Of the varieties that I have grown, I highly recommend ‘Sayamasume,’ ‘Shironomai,’ ‘Shirofumi,’ ‘Beer Friend,’ ‘Butterbeans’ and ‘Tohya’ as the sweetest and nuttiest. ‘Envy,’ developed by Elwin Meader, is extremely early, good flavored, and has very dark green seeds. ‘Black Jet’ and ‘Lammer’s Black’ are black seeded varieties that mature to dry seed in 105 days. The Seed Saver’s Exchange 2002 Yearbook (which lists seed offered by and available to members) listed 64 soybean varieties.


Ashworth, Suzanne, Seed to Seed. Chelsea Green Pub. Co., 2002.

Fedco Seeds 2003 catalog, PO Box 520, Waterville ME 04903-0520

Johnny’s Selected Seeds 2003 catalog, 955 Benton Ave., Winslow ME 04901-2601

Larcom, Joy, Oriental Vegetables; The Complete Guide for the Gardening Cook. Kodansha International, 1991.

Mcgee, Harold, On Food and Cooking; The Science and Lore of the Kitchen. Charles Scribner and Sons, New York, 1984.

Rodale, J.I., and staff, editors, How to Grow Fruits and Vegetables by the Organic Method. Rodale Press, 1961.

Seed Saver’s Exchange 2002 Yearbook, SSE, 3076 North Winn Rd., Decorah, Iowa 52101; $30.00 annual membership fee

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