A bean's germination timeline depends upon the type of bean and the provided growing conditions. First, the seed coat cracks and softens, allowing the primary root to take hold in soil and the seed leaves to emerge. Next, the stem arches so that the seed head is still bent to the ground but the stem is exposed to light. Last, the stem straightens and the seed becomes a maturing plant.
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Within a week's time, you can tell if stored seeds of undetermined age can germinate. Washington State University horticulturists suggest placing 10 seeds on a moist paper towel. Seal the paper towel inside a plastic storage bag and leave, undisturbed, for seven days at room temperature. If fewer than half the seeds germinate, do not sow the seeds.
Seed Coat Softens
Common outdoor garden beans–such as pole beans, bush beans, wax beans and runner beans–and uncommon beans like edamame ( a specialty soybean) and haricot vert, a French bush bean, aren't soaked prior to planting. Softening the seed coat prior to garden planting exposes the seed to disease. Allowing the seed to soften naturally takes more time than jar sprouting. Most beans begin to sprout within seven to 14 days of planting if the soil is warm (60 degrees Fahrenheit or more) and watered.
Bean plants usually have large, thick cotyledons, or seed leaves. These are not true leaves, but they provide a growing plant with nutrients. When a plant matures to the point of growing true leaves, the cotyledons drop off. Degradation of the cotyledons begins within the first day of sprouting. Within five days, mung beans lose their cotyledons entirely. Once the seed leaves drop the plant's stem straightens. The bean plant enters adulthood.
By the 21st day in the ground, the mature plant forms seed pods. The beans are ready to harvest within 60 to 75 days.