To grow soybeans, sow seeds in the spring two to three weeks after the last frost when the soil has reached at least 60 degrees Fahrenheit. Plant seeds 1 to 2 inches deep, and 2 to 4 inches apart in rows 24 to 30 inches apart.
Soybeans grow best in areas with an average daytime temperature between 60 and 70 degrees Fahrenheit. Soybeans are not frost-resistant.
Before sowing, add aged compost to planting beds. After sowing, keep soil moist until soybeans have sprouted. During flowering and pod formation, water regularly. Avoid overhead watering, as it causes damage to soybean flowers and seed pods.
At mid-season, add more aged compost to the planting bed. Avoid adding nitrogen-rich fertilizers, as it disrupts the growth of soybeans and other legumes.
Do not handle soybeans when they are wet, as this can spread fungus spores which cause infection in plants. Weed regularly without disturbing the soybean plants' shallow root systems. Rotate soybeans and other legumes at least every three years to prevent disease and enrich soil.
To harvest green shell beans, pick when the seed pods are green and plump. For fresh-use soybeans, harvest 45 to 65 days after sowing. To harvest dry soybeans, pick the entire plant after 100 days or more and hang it to dry.