Where to plant
Soybeans prefer well-drained soil and full sun. Plants grow 2 to 2 ½’ tall and can get bushy, but as a few plants can provide a meal or two for your family they deserve a space in even a small kitchen garden.
Most soybeans grown in the U.S. are genetically modified (94% of them in 2016, per the USDA). If avoiding GMOs is important to you start by buying organic seed or seed from a seed company that sells no GMOs. (Here are 6 GMO myths, busted) Then think about your neighbors: If there are farmers growing fields of soybeans within a few miles of your garden you may want plant your seeds at least a couple of weeks later than your neighbors so their fields will have finished flowering before your plants start. Why? While soybean flowers are typically self-fertilized, meaning the pollen produced by one flower stays in that flower and pollinates itself, some cultivars have flowers that do open sometimes, so insect transport of pollen is possible.
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If you want to be able to enjoy your crop of soybeans fresh, look edamame (vegetable-type) cultivars, which have been selected to have larger, tastier, faster-cooking immature seeds than field-type cultivars, which are typically harvest when mature and dry and used to make tofu and soymilk.
Your local garden center may have a cultivar or two of edamame soybean seed but if you are looking for organic seed or more variety, you may have to turn to mailorder sources. Johnnys Seeds has organic ‘Butterbeans’; High Mowing Organic Seeds stocks Midori Giant, Shirofumi, and Chiba; and Seed Savers Exchange carries ‘Agate’ (very early, so good for early crops and for gardeners with short growing seasons), ‘Envy’, and ‘Friskeby’.
When to plant
Make your first planting after the last frost and once the soil reaches 60 degrees. As noted above, you may wish to delay a couple of weeks longer if you live in an area with farms that grow a lot of soybeans.
Because soybean plants only flower for a brief period, all the pods will be ready to harvest within a week or so of each other. They don’t stay at the perfect harvest stage for more than a few days, so for a continuous supply you may want to plant some edamame every 10 days to 2 weeks up until about 2 months before your average first fall frost date.
How to plant
Inoculate your seeds with Rhizobium japonicum, an inoculant labeled for soybeans: check the label for application instructions, some get applied to the seeds, others get sprinkled into the planting holes or row. The inoculant contains a bacteria (which occurs naturally in some soils) that stimulates the formation of nodes on the plant's roots that enable the plant to extract nitrogen from the air, allowing the plant to virtually feed itself—a phenomenon called "nitrogen fixing."
Plant seeds 1” to 1 ½” deep and 8 to 16 seeds per square foot or 8 to 10 seeds per foot in rows.
Keep soil moist until seedlings are established then water only if soil gets very dry.
Harvesting edamame (green soybeans)
One easy way to enjoy fresh soybeans are as edamame, which are simply immature green soybeans. Simply steamed and salted, then popped out of the pod, they are a tasty, protein-packed snack. The name comes from Japanese “eda” meaning branch or stalk and “mame” meaning beans, reflecting how the beans are often sold in fresh markets.
Similar in appearance to baby lima beans, edamame have a sweet, nutty taste and a firmer texture than limas. They are high in protein (one cup of shelled edamame has 14-20 grams of protein per the USDA Food Composition Database, while baby lima beans have 12, and shelled green peas have 9), calcium, iron, and vitamins (particularly A, B1, B12, and C). You can substitute shelled edamame in any dish calling for peas or baby lima beans. (Here are the 20 highest-protein vegetarian foods.)
Most pods on a plant ripen at the same time typically 35 to 40 days after the crop first flowers appeared. Handpick individual pods daily when the beans are plump and just as the pods begin to lose their bright green color for maximum harvest. Or, for easier harvest, cut all the plants in a planting off near the soil line when most of the pods are at the perfect stage (a few will have started to yellow and a few will still have undersized beans in them) and retire to a comfortable chair in the shade to pick the pods off the stems.
Pods can be refrigerated for up to 3 days, though flavor starts to degrade noticeably in as little as 10 hours. Keep fresh pods in a bag to maintain high humidity. If you can’t eat your edamame the same day as harvest it is best to blanch them for 2-3 minutes in boiling water to stop the enzyme activity that causes them to degrade and either refrigerate them to use within the next week or freeze them loose (in or out of their pods) in airtight containers for later.
Be sure to toss the leafy stems into your compost pile as they are very rich in nitrogen; you may even want to grow soybeans just as a green manure cover crop.
Cooking and eating edamame
Boil or steam edamame pods in hot water until the beans are easy to pop out of their pods (usually about 4-5 minutes) as shelling is much easier after cooking – just pinch the pod and pop the beans out. The pods are not edible.
To eat as is, sprinkle the pods generously with salt or your favorite seasoning blend so that when you pop or squeeze the beans out into your mouth you’ll taste the salt or spices too. You can also shell the cooked beans in the kitchen and add to other dishes or sprinkle on salads.
Harvesting dry soybeans
If you miss the harvest window for edamame you can either pull and toss the plants into your compost pile or you can allow them to ripen and harvest the mature, dry soybeans. Dry soybeans are ready to harvest when at least 90% of the leaves have fallen off and the pods are dry. Plants can stay in the garden to dry, even after frost, but you may want to cut and dry the plants under cover if weather is wet. Cut plants off at the soil line or pull the plants out by the roots. Shell the beans out of their pods by hand individually; or by holding several plants by the base of the stems and banging them back and forth inside a barrel or trash can; or by putting the plants into a large, closed bag and stomping on it. Sort the beans out of the bits of leaf and stem material and store in an airtight container.