Although commonly associated with Japanese cuisine, it’s believed that soybeans may have originated in China around 1000 BCE. Aside from being an excellent source of protein and oils, soybeans are also a fantastic cover crop as they can fix nitrogen and improve soil quality. While there are many varieties of soybean, which vary in size and viability in different climates, most types possess green, furry seed pods that follow white or lilac blossoms, grow to 1.5–3″ long, and contain 2–3 beans each. Each plant will produce several dozen easy-to-shell pods most often used for human consumption as tofu, soy sauce, milk, or as a main ingredient in animal feed.
Black Jet is an easy-to-grow soybean best used as a dry bean. Bushy, upright plants reach about 2 to 2.5 feet tall and produce high yields of thin-skinned black soybeans, which are said to be better tasting and easier to digest than their yellow- or brown-skinned relatives. Fairly early maturing and hardy, they’re a good choice even in cool climates and regions with short growing seasons. Each pod has an average of 2 or 3 seeds contained inside.
Seed Depth: 1″
Space Between Plants: 4–6″
Space Between Rows: 2′
Germination Soil Temperature: 60–80°F
Days for Germination: 7–10
Sow Indoors: Not recommended.
Sow Outdoors: 1–2 weeks after average last frost. Successive sowing every 2 weeks for continuous supply.
Note: Seeds must be inoculated with a soybean inoculant containing Rhizobia bacteria in order to fix nitrogen.
Vegetative: Soybeans can be propagated from shoot cuttings in a hydroponic environment.
Best adapted to a climate with moderate temperatures and will not survive frosts or excessive heat. They also do not grow well in a wet environment. Daytime temperatures between 60–70°F are ideal. If you live in an area with warm winters, soybeans can be planted in late fall.
Natural: Prefers full sun. Will tolerate partial shade.
Artificial: Photoperiod, or day length, is a regulator of flowering time, so mimicking natural sunlight patterns will help your plants grow flowers and produce healthy pods.
Soil: Prefers a loose well-drained soil with a high amount of organic matter. A pH between 6.0–8.5 will keep plants healthy and nourished. Because of their nitrogen-fixing abilities, soybeans will tolerate poorer soils.
Soilless: Will grow in a soilless mix.
Hydroponics: Will thrive in aquaponic or hydroponic systems, including NFT systems and media beds.
Water: Requires regular and even moisture, particularly during flowering. If seeds are too moist, they may crack and fail to germinate, so take care not to overwater when planting. Avoid heavy watering from above, as this may damage or knock off flowers or pods.
Nutrients: Requires moderate to low levels of nutrients. Avoid adding too much nitrogen, and if needed, use a fertilizer containing more phosphorus and potassium. Soybeans will fix nitrogen if the correct soil bacterium are present. Use compost to amend soil prior to planting and sidedress plants in the middle of the season.
Foliar: Foliar sprays of nitrogen, boron, magnesium, and manganese have been shown to increase yields.
Mulching: Mulch such as straw will help keep soil moist and reduce weeds.
Deficiency(s): Phosphorus and potassium may be supplied using organic fertilizers. Proper inoculation with Rhizobia bacteria is necessary for the plants to fix nitrogen.
Rotation: Practice a 3-year crop rotation of soybeans with other crops in order to break insect and disease life cycles.
Companions: Grows well with potatoes, cucumbers, corn, strawberries, celery, and summer savory. Avoid onions and garlic.
Harvest: Pick soybeans when pods are plump and still green for use as edamame or as a shelling bean. About a month later, after most of the plant’s leaves have died back, you can harvest the hardened dried pods. The pods should be hung in an area with low humidity until fully dry. Dried soybeans can be easily separated from their pods by placing the whole pods in a bag and shaking.
Storage: Fresh green soybeans will keep for up to a week in the refrigerator. Dried, shelled beans can be stored for 10–12 months in a dry, cool space.
SEED SAVING: Saving your own soybean seeds is easy since the flowers are self-fertile. This means they won’t cross-pollinate, and you can be sure that the seed’ll grow true to the variety you harvest it from. It’s best to dedicate an entire section of your soybeans for seed saving purposes rather than harvesting first and only saving the pods that develop later. That way, you’ll be sure to have all of the healthiest seeds for planting next year and not only the smaller and less vigorous remnants.
Fun Fact: The black soybean is an ingredient in a traditional New Year’s dish in Japan called Kuromame; mame means health and represents good health in the New Year.
PRESERVE: Can be blanched and frozen either whole or shelled. If canning, you must use a pressure canner. If starting with raw beans, leave 1″ of headspace to allow for expansion. Otherwise, fill the jar to within 1/2″ of the top. Fill with boiling water or the water you used to cook the beans. You can also pickle edamame.
PREPARE: To make edamame, whole green pods are boiled in salt water until tender, and the beans are removed from their fibrous pods for consumption. Soybeans can also be prepared to make miso, soy sauce, tofu, tempeh, soy milk, and soybean sprouts. Usually these processes are not undertaken by the home gardener since these products require fermentation, which helps to make soybeans easier to digest. If you save your dry beans, they will require an overnight soak prior to cooking. Changing the soaking water 1–2 times is also helpful.
Nutritional: Contains a high amount of complete protein. They are a good source of vitamin(s) A, B, calcium, iron, dietary fiber, and essential fatty acids, including omega-3s.
Medicinal: Contains phytochemicals and antioxidants which may have cancer fighting properties. Fermented soybeans have been used historically to treat colds, fever, headaches, insomnia, and irritability. The healthy fats found in soybeans are also useful for treatment of high cholesterol. Because of their isoflavones, which are estrogen-mimicking chemicals, soybeans may help lower the risk of developing hormone-related cancers. Soybeans are also being investigated for their effects on helping to reduce symptoms of menopause and the risk of osteoporosis.
Warnings: All soybeans must be cooked prior to consumption to destroy trypsin inhibitors, which prevent the digestion of proteins. Sprouted beans must be boiled for at least 5 minutes. Green soybeans should be blanched for a few minutes in boiling water.
Serve up your black soybeans with some Korean influence by following this recipe for Braised Black Soybeans.