Soybeans are tender warm-weather legumes. Sow soybeans in spring 2 to 3 weeks after the average last frost date when the soil has warmed to at least 60°F. Soybeans can be planted earlier in warm-winter regions. Soybeans grow best where the daytime temperature averages in the 70°sF.
Description. The soybean is a bushy, free-branching annual legume. It grows 12 to 36 inches tall. Stems and leaves are hairy. Flowers are white with lavender shading. Pods grow 1 to 4 inches long in clusters of three to five. Each fuzzy pod contains 2 to 4 seeds. There are more than 10,000 soybean cultivars. Colors range from black to gray, brown, green, yellow, white, and striped. Seeds can be smaller than a pea or as large as a kidney bean.
Yield. Grow 4 to 8 soybean plants per each household member.
Site. Plant soybeans in full sun; soybeans will tolerate partial shade but the yield will be reduced. Soybeans grow best in loose, well-drained soil rich in organic matter. Soybeans prefer a soil pH of 6.0 to 6.8. Soybeans are tolerant of poor soil.
Planting time. Sow soybeans in spring 2 to 3 weeks after the average last frost date when the soil has warmed to at least 60°F. Soybeans grow best where the daytime temperature averages between 60° and 70°F. Plant soybeans in late winter in warm-winter regions. Soybeans are not frost-tolerant.
Planting and spacing. Sow soybean seeds 1 to 2 inches deep, 2 to 4 inches apart in rows 24 to 30 inches apart. Thin successful seedlings from 4 to 6 inches apart; cutaway thinned seedlings with scissors at ground level being careful not to disturb the roots of remaining plants. Do not soak seed before planting and do not overwater immediately after planting; too moist seeds may crack and germinate poorly.
Companion plants. Potatoes, cucumbers, corn, strawberries, celery, summer savory. Do not plant soybeans with onion or garlic.
Caring for Soybeans
Water and feeding. Keep planting beds evenly moist until soybeans have pushed through the soil. Water regularly during flowering and pod formation. Avoid overhead watering which can cause flowers and pods to fall off. Mulch when the soil warms to greater than 60°F to conserve soil moisture. Add aged compost to planting beds in advance of planting. Side dress soybeans with aged compost at midseason. Avoid adding nitrogen-rich fertilizers to planting beds. Soybeans, like other legumes, set up a mutual exchange with soil microorganisms called nitrogen-fixing bacteria to produce nitrogen compounds used by the plant.
Care. Avoid handling soybeans when they are wet or covered with heavy dew; this may spread fungus spores. Keep planting beds weed-free; cultivate around soybeans carefully so as not to disturb the plant's shallow root system. Mulch to conserve soil moisture once the soil has warmed. Rotate soybeans and other legumes to add nitrogen to the soil.
Container growing. Soybeans can be grown in containers 8 inches deep, the space required for a useable crop makes soybeans a poor choice for container growing.
Pests. Soybeans are rarely bothered by pests. Keep the garden clean and free of debris so that pests can not harbor or over-winter in the garden.
Diseases. Soybeans are rarely attacked by a disease. Rotate beans so that they do not grow in the same location more than every three years.
Harvesting and Storing Soybeans
Harvest. For green shell beans, harvest soybeans when pods are green, full, and plump, usually 2 to 3 inches long, about half mature. Soybeans for shelling and fresh use are ready for harvest 45 to 65 days after sowing. Dry soybeans require 100 or more days to reach harvest. Soybeans reach maturity at the same time; pull the whole plant and hang it upside down to dry. Shell dry beans once the pods are fully dry.
Note: Soybeans should not be eaten raw; they contain trypsin inhibitor which prevents the digestion of proteins. Blanch green soybeans in boiling water for a couple of minutes and then plunge them into an ice-water bath. Boil sprouted beans for at least 5 minutes before eating.
Storing. Green shelled or unshelled soybeans will keep in the refrigerator for up one week. Shelled soybeans can be frozen, canned or dried. To make shelling easier, drop pods into boiling water for a minute. Dried, shelled soybeans can be stored in a cool, dry place for 10 to 12 months.
Varieties. There are more than 10,000 soybean cultivars. Green-seed cultivars are considered the most tender and best flavored. Black-seeded beans are used for drying. Yellow-seed beans are used to make soy milk and flour. Select a cultivar suited to your growing region; check with the nearby agricultural extension for recommendations.
Common name. Soybean
Botanical name. Glycine max
Origin. East Asia