Provided that you live in an area where you have at least three months of above-freezing weather per year, you can grow soy beans. There are two main types of soy bean: grain and vegetable. Grain types are used for seed and animal feed, whereas vegetable types are the ones you would grow to harvest and eat from your garden. Both require the same types of planting and growing conditions. However, once they have reached their edible stage, vegetable-type soy beans should be harvested within five days to retain peak flavor.
Prepare your garden bed in an area that gets full sun. Dig soil to a depth of 1 foot, making sure to break up any clumps.
Mix compost into the garden soil in a 1:1 ratio about a week before planting. Mix 1/3 manure into the soil as well. Soy beans like a very rich soil with good drainage. If your soil has poor drainage, consider amending it with vermiculite, perlite, peat moss or coir. Be aware that vermiculite poses potential health risks associated with asbestos exposure. There are environmental sustainability concerns regarding peat moss, as well.
Sow soy beans directly in your garden after all danger of frost has passed in your area. Beans should be sowed 2 inches apart, to a depth of 1/2 inch. If planting in rows, plant about 2 feet apart.
Apply a side dressing of a nitrogen-rich vegetable fertilizer at the time of planting. Soy beans require consistent fertilization to grow, and are heavy nitrogen feeders. Apply fertilizer every week or so according to package directions for strong, vigorous growth. Nitrogen-rich fertilizers can be recognized by reading their nitrogen-phosphorus-potassium (NPK) numbers. If the first number is higher than the other two, this indicates it is high in nitrogen.
Water gently, using a "mist" or other low-pressure setting on your garden hose sprayer. Using these settings allows you to water without disturbing seeds or soil. Water consistently and keep soil moist but not flooded during the life of the plants.
Harvest when seed pods visually appear full and are a shiny, bright green. When they start to pale or turn yellow, they are approaching full maturity and will taste bitter. The best taste window is about five days, though it may vary by the variety of soy bean planted.