Soybean, lentil and pinto bean seeds grow rapidly, but the time it takes for a bean seed to germinate depends in part on where it sprouts. Germination of a seed in garden soil is measured from the day the seed is planted until just before its first shoot emerges above the soil. Germination outside the soil in a sprouting jar or other container usually is much shorter. Sometimes this is done as part of a science project or to produce edible sprouts.
Soybeans are a good model for a science germination experiment, because they sprout in three to four days in petri dishes, according to the Science Project Lab website. But Michigan State University notes that germination in the soil takes six to 14 days. Cold and excess or inadequate moisture are among the conditions that can slow germination outdoors. Living Gently Quarterly notes that soybean sprouts are becoming more common in cooking. But it warns not to sprout commercial seeds intended for planting, because they are chemically treated.
The Sprout People website says it takes two to three days to germinate lentil seeds in sprouters, which are typically lidded containers with holes for air circulation. If growing in the garden, lentil seeds germinate in about 10 days at 68 degrees Fahrenheit, according to the Harvest to Table website. They are hardy annuals and members of the pea family. Sprouting any bean seed involves a process of soaking and regularly rinsing the seeds until they germinate in a sprouter that is kept out of direct sunlight and stored at 70 degrees Fahrenheit. Lentil sprouts can be eaten raw or cooked.
In soil, pinto beans germinate in four to eight days, according to the Texas A&M University Extension. But Sprout People says that when germinated in a sprouter, the process only takes 2 to 4 days. Unlike soybean and lentil sprouts, pinto bean sprouts are not edible unless cooked. Sprout People says they add a "delicate sweetness" to soup and that the process of sprouting alleviates some of the gaseousness associated with beans.