Soybeans are in the legume family of plants, and like most legumes, they are excellent to grow for improving soil quality--particularly fixing nitrogen from the air to the soil. Soybeans are extremely nutritious food for both humans and animals because they contain protein, carbohydrates and fats and crucial vitamins such as calcium and iron. The combination of healthy for eating and healthy for the soil makes them a popular addition to any home garden.
Soybeans will provide the best growth results and harvest yields if they're planted when the soil temperature is between 55 and 60 degrees Fahrenheit. This temperature or warmer allows the seeds to germinate quickly.
While soybeans will grow in almost any type of soil, they do best with fertile loam that's loose and well-drained.
Healthy, fertile soil will be loose enough for the seedlings to break through the surface as they sprout. It will also help the soybean plants absorb and retain water and nutrients, plus there are beneficial organisms such as algae and worms that help balance the nutrients and minerals needed for the plants to grow well.
Soybeans can be planted from 1 to 2 inches deep depending upon how moist the soil is and how large the soybean seed is. Larger seeds can be planted at slightly deeper depths, but generally soybean seeds are planted at 1 to 1 1/2 inches below the surface unless the soil is sandy or doesn't have enough moisture in it. In those cases the seed can be planted 2 to 2 1/2 inches.
According to the National Soybean Research Laboratory, soybean seeds are generally planted from 1 to 4 inches apart in narrow rows so that the soybean canopy completely joins together at flowering time. This growth canopy shades the soil and prevents weeds from growing.
Soybeans take longer to grow than standard garden beans, and they generally require warmer weather as well. Depending upon the amount of warmth available, soybeans take three to five months to fully mature. Because growth is slower in cooler regions, the NSRL recommends planting early maturing varieties in northern gardening regions.
Five to 10 days after planting soybean seeds, they will emerge from the ground as seedlings. They will continue to grow vegetation for six to eight weeks, while also growing the root system. In lose, well-drained soil a soybean tap root can grow down as far as 5 feet.
Towards the end of the vegetation growth stage, flowers begin to appear. Very small clover-like flower buds will develop at the node stems. Each flower is about 1/4 inch in size and may be pink, purple or white in color.
One to two weeks after flowers appear pods will form with three to four seeds each. These seeds will fully mature in 30 to 40 days, and are ready for harvest when the pods have turned completely yellow.