The peanut plant is unusual because it flowers above ground but the fruit (peanut pods and seeds) develops below the ground.
Peanut seeds (kernels) grow into a green oval-shaped plant usually about 18 inches tall which develop delicate flowers around the loser portion of the plant. Peanut plants begin to bloom about 30 to 40 days after emergence. The small, bright yellow flowers are pea-like in appearance. The flowers pollinate themselves (self-pollinated). The petals begin to fall as the fertilized ovary begins to enlarge. After pollination and fertilization occurs, the small stem or stalk known as the “peg” below the fertilized ovary elongates and curves downward and starts moving into the soil. It takes about 10 days for the peg to penetrate into the soil.
The peanut embryo is in the tip of the peg. A week after soil penetration, the peg tip enlarges and pod and seed development begin (right on the tip of the peg). The embryo turns horizontal to the soil surface and begins to mature taking the form of the peanut. The plant continues to grow and will eventually produce 40 or more mature pods.
With warm temperatures and favorable moisture conditions, the fruits (seeds) mature in 70 days or so. From planting to harvesting takes from 140-160 days depending on peanut type and variety planted. Since the peanut plant produces flowers over several weeks, all of the pods do not mature or ripen at the same time. The objective is to harvest the greatest number of mature pods and seeds.
Oklahoma Peanut Commission