Soybeans are a member of the legume family; however, they grow more slowly than most common garden beans. Soybeans need warmer air and soil temperatures and a longer growing season than most garden bean varieties. When you grow soybeans in a cooler region, they will grow more slowly. For this reason, gardeners who live in cooler growing regions should choose soybeans that mature earlier for best results. Plant soybeans at the same time as tomatoes for best harvesting results.
Soybean Germination and Emergence
After planting, the soybean seeds absorb moisture from the soil rapidly. Within 2 days, the radicle pushes through the seed coat and becomes the first root of the new soybean plant. Within 5 days of planting, the stem of the soybean emerges from the soil in a bent-over "hook."
As the stem continues to grow, the tip of the stem will pull up out of the soil and the stem will straighten out. On this new stem are the cotyledons, which are the initial leaves of the new soybean plant. The cotyledons provide nutrients during this initial period until the true leaves form. After the first true leaves grow, the cotyledons fall off the soybean plant. If soil and temperature conditions are not ideal during this period, the soybean plants may not germinate and grow.
The Vegetative Period
After the soybean seedling germinates and emerges from the soil, it grows quickly. The two months after the soybean seedlings emerge from the soil are the vegetative period. At the same time as the stem and leaves of the seedling are growing up, the roots are growing down into the soil.
Lateral roots grow off the central taproot to formulate a large root system. Most of the roots stay in the top 12 inches of the soil, but some may grow down as far as 5 feet. Within two weeks of the seedlings emerging from the soil, the roots will be capable of providing for all of the soybean plant's nitrogen requirements.
The Flowering and Fruiting Stages
The flowering stage comes after the vegetative period. Soybean flowers fertilize themselves and as many as 15 flowers may grow at each stem node. The flowers may be purple, white or pink and up to 80 percent of the flowers will go on to produce bean pods.
Within 2 weeks of the flowers appearing, the bean pods will appear. Up to four beans are in each pod. This is a critical period for the soybeans and if temperature and moisture conditions are not ideal, the beans may not grow properly.
Beans Maturing and Harvest
As the beans mature in the pods, the moisture level of the soybean plant decreases. When the beans are completely mature, the foliage of the soybean plant turns yellow. The bean pod will also be yellow to indicate maturity. Soybeans are either harvested while still green for edamame (green soy beans) or when they are yellow for animal feed or food processing uses.