How Do Soybeans Pollinate?

Flower Production

• Soybean is primarily a self-pollinating plant with some pollination also done by bees. The time of planting and weather conditions determine the blooming time. Flowers usually appear by midsummer, often a little earlier in warmer weather than under cooler temperatures. The determinate varieties do not start to flower until the plant reaches mature height. In all cultivars, only 25 to 50 percent of the flowers are pollinated and produce pods. Flowering generally lasts for three to four weeks with pods appearing within 10 to 14 days of first flowers.

Flower Structure

• The flowers grow in the form of clusters consisting of three to 15 flowers and appear from the axils of branches. Flower structure is referred to as Papillionadae with a single, large petal, two wing petals and two keep petals. The pistil in the center is surrounded by 10 stamens with nine fused in a tubelike form. The single stamen close to the standard petal bears the pollinating structure called a stigma. The very small, 1/4-inch flowers are white, pink or purple and are like pea or clover flowers in appearance.

Pollination Process

• The flowers of soybeans are pollinated a little before or after the flowers bloom when the stigma sheds the pollen. The time of pollen shed is usually between 7 and 9 a.m. with a temperature of 86 degrees Fahrenheit or higher. Under moderate temperature, flowers are pollinated from late morning and throughout the day. The rate of pollination reduces under cooler temperatures.

Pod Development

• As soon as the flower is pollinated, the development of the pod begins. It takes about 40 days for pods to reach mature size. Once the pods are mature, the seeds start to develop inside. This stage lasts for another 40 days. The pods are ready to harvest when the seeds are grown and before the color changes to yellow.