Soybean

The edamame page covers soybeans harvested green, while you’re still in the flavor window. This page is for the same plant harvested dry - seeds rattle in the pod, leaves have dropped, season is over. Same species, completely different product and completely different reason to grow it. Start here if you’re growing for tofu, soy milk, miso, or specialty varieties you can’t buy anywhere.

What It Actually Is

Glycine max is an annual legume in the family Fabaceae, domesticated in eastern China approximately 3,000 years ago. Archaeological evidence places the earliest cultivated soybeans in the Yellow River Valley during the Shang Dynasty period; by the first century CE it had spread across East Asia as a staple crop. It arrived in the United States in the early 1800s and became one of the most important commodity crops in American agriculture.

The scale is worth stating plainly. USDA NASS 2022 data: US farmers harvested 87.5 million acres of soybeans at an average yield of 49.5 bushels per acre - roughly 3,000 lb per acre. Soybean is the second largest US crop by planted acreage after corn. Virtual all of it goes to animal feed or industrial processing. The commodity price floats around $0.50-1.00/lb at the farm gate. Home garden soybean competes with none of that. The commodity market is not your reference point.

The distinction between edamame and dry soybean is entirely harvest timing. Edamame is the same plant, harvested at 80-90% pod fill - roughly 70-80 days from direct sow - when seeds are plump, green, and sweet. Dry soybeans are harvested when the pods have turned tan or brown on the plant and the seeds inside rattle, 90-120 days depending on variety. At the dry stage, the sugars have converted to starch and protein, the flavor is neutral and beany, and the seed is shelf-stable. The product going into your jar at harvest has almost nothing in common with what you ate as edamame six weeks earlier.

The reasons to grow each are different, and those reasons belong on separate pages.

Why Grow It at Home

Three arguments, stated without embellishment.

Variety control. The specialty soybean types worth growing - black soybeans (kuromame), heirloom yellow strains bred for tofu-making, cream-seeded Japanese types optimized for soy milk - are largely unavailable as dry beans outside specialty importers. A bag of black soybeans at a Japanese grocery store runs $8-15/lb when it appears at all. Most standard grocery stores don’t stock it. If you want to make traditional Japanese New Year kuromame with black soybeans you grew, or you want to press tofu from a specific high-protein heirloom variety, the supply chain doesn’t exist commercially. Home growing is the only option.

Fresh processing. Dry soybeans from the grocery store were harvested months ago, stored in warehouses, and have been sitting on a shelf in a clear plastic bag under fluorescent light. For tofu and soy milk made from whole soybeans, freshness affects flavor. Home-grown soybeans dried and processed within weeks of harvest produce a tofu and soy milk with noticeably cleaner flavor - less bitterness, more of the grassy sweetness that makes traditional Japanese preparations worth making.

Nitrogen fixation. Soybeans fix atmospheric nitrogen through a symbiotic relationship with Bradyrhizobium japonicum bacteria in root nodules. University of Minnesota Extension (Soybean Production in Minnesota, 2021) puts the fixation range at 40-80 lb of nitrogen per acre under good conditions. In a garden context, a bed of soybeans followed by corn, leafy greens, or brassicas benefits from the residual nitrogen left in decomposing root nodules. Most crops deplete. Soybeans deposit.

Inoculant - Don’t Skip This

If you’ve never grown soybeans or edamame in a particular bed - or haven’t grown them in three or more years - the Bradyrhizobium japonicum bacteria necessary for nitrogen fixation may be absent or present at insufficient levels. The plant will grow without them. It will not fix nitrogen without them, and yield will be meaningfully lower.

Inoculant is a powder or granular product containing live Bradyrhizobium japonicum cultures. Granular forms cost $3-6 at farm supply stores and online seed suppliers - enough to treat a full home garden planting with a single purchase. Liquid formulations also exist and perform comparably.

How to inoculate: moisten soybean seeds slightly with water. Add inoculant per package directions and coat seeds evenly. Sow within 24 hours. The bacteria in the inoculant die when the coated seeds dry out, and UV kills them if you let inoculated seeds sit in sunlight. Get them in the ground the same day or the next morning. Purdue Extension (Soybean Inoculants, AY-217) documents yield responses of 10-20% in uninoculated soils, with the response strongest in soil that has never grown soybeans.

After germination, you can check whether nodulation happened: pull a plant and look at the roots. Pink or reddish nodules indicate active nitrogen fixation. White nodules indicate the bacteria are present but fixation is limited. Absent nodules mean fixation isn’t occurring - consider inoculating for the next planting or switching beds.

If you’ve grown soybeans in the same bed within the past two to three years, Bradyrhizobium populations may still be present at functional levels. Inoculation is still worth doing; the cost is trivial and the downside risk of skipping it is real.

Variety Selection

Most commercial soybean varieties are commodity types, bred for yield and mechanical harvest compatibility. Those aren’t what you want for home garden dry-bean use. Seek out varieties with flavor, color, or protein profiles that justify the growing time.

Variety	Days	Seed type	Yield	Primary use	Notes
Butterbean	90-100	Yellow, large-seeded	High	General dry bean, tofu	Large bean; easy to shell; widely available; good starter variety
Black Jet	85-95	Black-seeded	Medium-high	Japanese cooking (kuromame), black bean recipes	Standard for New Year preparations; needs full season in Zone 5-6
Envy	75-80	Green-seeded	Medium	Edamame or dry bean	Dual-purpose; harvest green for edamame or let dry; compact plant
Shirofumi	95-110	Cream/beige	High	Tofu-making, soy milk	Bred for tofu; high protein; Japanese selection; less common in US catalogs
Vinton 81	100-115	Yellow	Very high	Dry bean, general use	Open-pollinated; developed for northern US; reliable in zones 4-6

Sources: Johnny’s Selected Seeds variety descriptions; USDA ARS soybean germplasm collection.

One note on sourcing: Shirofumi and similar tofu-bred varieties are harder to find. Fedco Seeds, Kitazawa Seed Company, and Fruition Seeds carry Japanese-type soybeans that the large seed retailers typically don’t stock. If your goal is tofu-making, search specifically for varieties described as tofu-type or natto-type rather than general-purpose dry beans.

Maturity Groups and Zone Compatibility

USDA classifies soybeans into maturity groups based on day-length sensitivity: group 000 at the far north to group X in the tropics. This matters for home gardeners because planting a group 5 soybean in Minnesota means it will never reach maturity - the variety needs day lengths that don’t occur that far north.

Practical guide by zone:

Growing zone	Recommended maturity groups	Notes
Zones 3-4	Groups 00 to 0	Short-season only; look for 75-85 day varieties
Zones 4-5	Groups 0 to 1	Group 1 is the limit for reliable dry harvest in most years
Zones 5-6	Groups 1 to 3	Most broadly adapted range for Eastern US home gardeners
Zones 6-7	Groups 3 to 5	Hot summers allow longer-season specialty types
Zones 7-8	Groups 4 to 6	Full range of specialty varieties available

Most catalog varieties sold to home gardeners fall into groups 1-3 and are broadly adapted to zones 5-7. If you’re in zone 4 or colder, check days-to-maturity carefully and prioritize varieties at 85 days or under.

Growing Requirements

Direct sow after last frost when soil temperature is at or above 60°F. The Bradyrhizobium inoculant is heat-sensitive; in hot soil above 85°F it can lose viability quickly after coating - sow promptly when soil is in the 60-75°F range. Cold soil means slow germination and seeds sitting in damp ground long enough to rot.

Sow 1 to 1.5 inches deep, 3-4 inches apart in rows 18-24 inches apart. Thin to 6 inches after emergence. Soybean roots develop the nitrogen-fixing nodule system during early establishment and don’t transplant well - direct sow is the right approach. Germination takes 6-10 days at 70°F soil temperature.

Target soil pH of 6.0-6.8. Well-drained soil is not optional - soybeans do not tolerate waterlogged conditions and will develop root rot in heavy clay that stays wet. If your soil is heavy clay, amend with compost and consider raised beds or raised rows. Phosphorus and potassium at planting support root and pod development; nitrogen fertilizer is unnecessary and counterproductive once inoculation is established.

Water 1 inch per week throughout the season. The critical period is pod fill: roughly a 2-3 week window when seeds are expanding inside pods. Drought stress during pod fill directly reduces seed size and yield. If you can only irrigate once in a dry stretch, do it during pod fill. The plants tolerate drier conditions during vegetative growth and after pod fill begins to slow.

Most garden soybean varieties are determinate - they set the bulk of their pods in a single flowering flush rather than continuing to flower as they grow. Indeterminate types exist but are less common in home garden catalogs. Determinate plants reach full size and stop, which makes them easier to manage and harvest cleanly.

The ROI Case

The honest calculation splits into two very different scenarios.

Standard variety, commodity comparison: if you’re comparing home-grown yellow soybeans against the $1-2/lb bag of dried soybeans at the health food store, the math is not compelling. Three pounds of home-grown soybeans at $3.00/lb retail value returns $9.00 gross on $2.99 seed cost - about $6 net. That is a real return on seed investment but a modest savings against the commercial equivalent.

Specialty variety, specialty market comparison: black soybeans (kuromame) at Japanese specialty grocers and online importers typically run $8-15/lb. Heirloom yellow varieties marketed for tofu-making at natural food stores run $4-8/lb. The same 3 lb yield priced against specialty market equivalents returns a completely different number.

For tofu: 1 lb of dry soybeans yields approximately 1.5-2 lb of fresh pressed tofu. Fresh tofu at specialty markets and natural food stores runs $3-6/lb; premium fresh tofu at Japanese markets runs $4-8/lb. Processing adds value at every step.

Scenario	Yield	Price reference	Gross	Seed cost	Net	ROI
Standard variety, dry bean	3.0 lb	$3.00/lb (health food store)	$9.00	$2.99	$6.01	3.0x
Specialty variety (black, heirloom)	3.0 lb	$10.00/lb (specialty import)	$30.00	$2.99	$27.01	10.0x
Processed to fresh tofu	3.0 lb dry → 4.5-6 lb tofu	$4.00/lb	$18.00-24.00	$2.99	$15.01-21.01	6.0-8.0x
Standard variety vs. commodity	3.0 lb	$1.50/lb (bulk bin)	$4.50	$2.99	$1.51	1.5x

The bottom row is the scenario that doesn’t justify growing soybeans. Standard yellow soybeans competing against bulk-bin prices at the co-op is a break-even proposition at best. The cases that justify the growing time are specialty varieties and processed products - and those are exactly the cases where home growing is often the only supply chain available.

Harvesting for Dry Beans

The harvest window requires patience and timing. Pods need to dry completely on the plant, to the point where the seeds inside rattle audibly when you shake a pod. The pods will have turned from green to tan, brown, or mottled depending on variety. Leaves will have yellowed and dropped. The plant looks dead - that’s correct.

Don’t push harvest to 100% dry pods. Fully dry soybean pods shatter naturally - they split open and drop seeds - and once the first pods start shattering you’re losing yield with every day you wait. Harvest when 90-95% of pods have turned tan. The remaining green pods will continue drying off the plant.

If fall rain is approaching before the crop is fully dry, pull the entire plants and hang them upside down in a dry, well-ventilated space - barn, garage, covered porch - for one to two weeks. They’ll finish drying off the vine as long as they’re protected from rain and humidity.

Threshing: once pods are completely dry and brittle, put the plants in a clean barrel, tote, or large grain bag and beat them against the inside walls. Seeds will crack free from the pods. Alternatively, spread dried plants on a tarp and roll over them with a rolling pin or lawn roller. A flat clean surface works too - put plants in a burlap or mesh bag and beat the bag against the ground.

Winnowing: pour seeds slowly in front of a box fan outdoors. Seeds fall into your container; pod fragments and debris blow away. Repeat until the seeds are reasonably clean. A second pass improves purity. This step takes fifteen minutes and produces a clean result.

Storage: dry soybeans keep 1-2 years at good quality if stored at 12% moisture or below. The moisture test: press a thumbnail firmly against the seed. If you can’t dent the seed coat, moisture is at or below the target. Store in airtight glass jars or sealed food-grade containers in a cool, dry location. Avoid clear containers in direct light.

What Goes Wrong

Pod shattering is the main harvesting hazard. In a hot, dry September, pods may shatter before you get to them. Watch the field from 85 days onward and harvest when the tan pods start showing up. If you hear rattling and see splits in pods when you walk the row, harvest immediately.

Soybean aphid (Aphis glycines) was introduced to the US in 2000 and is now present throughout the country. Colonies form on undersides of leaves in July and August. Natural predators - lady beetles, parasitic wasps, lacewing larvae - provide substantial biological control in most years without intervention. If colonies are heavy enough to cause leaf curl or wilting, insecticidal soap applied directly to aphid colonies is effective and spares beneficial insects. Avoid pyrethroid insecticides on soybeans; they kill the beneficial insect populations that provide free biological control and create conditions for aphid explosions in subsequent weeks.

Bean leaf beetle (Cerotoma trifurcata) chews small, round holes in leaves throughout the season. At low-to-moderate populations, the damage is cosmetic and doesn’t affect yield. Heavy infestations on very young seedlings can stunt plants. Keep row cover over seedlings for the first three weeks if beetle pressure has been high in previous seasons.

White mold (Sclerotinia sclerotiorum) appears as fluffy white fungal growth on stems at the soil line and on pods, in cool, wet conditions. Infected stems develop a soft rot and the plant collapses. Remove infected plants immediately; don’t compost them. White mold produces sclerotia - small black resting structures - that persist in soil for years. Prevention is the only practical strategy in home gardens: 3-year crop rotation, good drainage, and adequate plant spacing for airflow.

Deer eat soybean foliage aggressively, particularly when plants are young and tender. A 10-foot row of seedling soybeans can disappear overnight. If deer pressure is present, row cover for the first four to six weeks is the practical answer. Repellent sprays work inconsistently. Physical exclusion works.

Companion Planting Context

The frontmatter lists Corn and Squash - this is the Three Sisters planting system used by many Native American agricultural traditions. Corn provides vertical structure; beans (historically pole beans, but soybeans in this context) fix nitrogen that benefits the corn; squash’s large leaves shade the soil surface and suppress weeds while retaining moisture.

The nitrogen benefit is real and documented - soybeans fix 40-80 lb/acre equivalent of nitrogen (University of Minnesota Extension, 2021), leaving residual fertility in the soil after harvest. Planting soybeans adjacent to or preceding corn makes agronomic sense.

The structural companion planting aspect is more complicated for dry soybeans. Determinate bush-type soybeans - which includes most garden dry-bean varieties - don’t climb and don’t need the corn for support. The Three Sisters design works better with climbing pole bean varieties. If you plant corn and dry soybeans together, treat them as beneficial neighbors in terms of soil fertility and pest habitat rather than expecting a vertical integration that won’t occur with compact bush types.

Squash as a ground companion still works alongside soybeans - the canopy effect is independent of what the bean plants do above ground.

---

Related crops: Edamame, Corn, Chickpea

Related reading: Perennial vs Annual ROI - nitrogen-fixing legumes and their multi-year soil impact