Peanuts are grown in the ground, a growth habit that is highly unusual compared to most common crops. Unlike potatoes or carrots, the peanut does not start as a root or tuber. Instead, the plant initiates its fruit above the soil and then actively buries it to mature. This unique reproductive strategy, known as geocarpy, makes the peanut’s development distinct.
Are Peanuts a Nut or a Legume?
Botanically, the peanut (Arachis hypogaea) is a legume, placing it in the same family, Fabaceae, as beans, lentils, and peas. Legumes develop inside a pod containing multiple seeds. They are also known for their ability to harbor nitrogen-fixing bacteria in root nodules, which improves soil fertility.
Peanuts are often grouped with tree nuts, such as almonds or walnuts, for culinary purposes due to their similar texture and high fat content. However, a true nut is a single-seeded fruit that does not open on its own and is protected by a hard, woody shell. Peanuts differ from this botanical definition, despite their common name.
The Pegging Growth Process
The peanut plant’s reproductive cycle begins with small, yellow flowers that appear above the ground, usually around 40 days after planting. These flowers are self-pollinating, and once fertilization occurs, the petals drop off. The fertilized ovary then begins to form a specialized structure called a gynophore, or “peg.”
This peg is a short, stiff stalk that elongates rapidly, curving downward until its tip penetrates the soil surface. The peg must successfully push the developing ovary into the darkness and moisture of the earth, often reaching a depth of one to seven centimeters. The failure of the peg to enter the soil results in the abortion of the fruit.
Once the tip of the peg is safely buried, the embryo at its end turns horizontal to the soil surface and begins to mature into the peanut pod. The pod requires the underground environment—specifically the darkness, moisture, and mechanical resistance of the soil—to fully develop into the familiar shell and kernels.
Harvesting and Curing Peanuts
After a growing season of typically 120 to 160 days, the peanuts are ready for harvest, signaled by the plant’s leaves turning yellow and starting to wilt. Harvesting requires specialized equipment, often called a digger. The digger is pulled through the field to sever the plant’s taproot and lift the entire plant from the soil. It then gently shakes the plant to remove excess soil and inverts it, laying it back down in a row with the peanuts exposed to the air.
This inversion process initiates drying, or “curing,” which must take place before the peanuts can be stored or processed. Freshly dug peanuts have a high moisture content, often ranging from 35 to 50 percent, which would lead to spoilage if not reduced. The plants are left in the field in these inverted rows, known as windrows, for several days to cure in the natural heat and air.
Curing reduces the moisture content to a safe level of around 8 to 10 percent. This reduction is essential for developing the characteristic flavor and texture of the peanut and preventing mold growth. After field curing, a combine machine separates the dried pods from the vines. The peanuts may then undergo a final, controlled drying process in wagons using forced warm air before they are sent for inspection and market.