The peanut, Arachis hypogaea, is not a true nut but a member of the legume family, which also includes beans and peas. This classification means the peanut is a seed contained within a pod, or technically a fruit, that develops in an unusual way compared to other legumes. The entire cultivation process is defined by one unique characteristic: the fruit bodies must develop underground, a phenomenon known as geocarpy. This requirement dictates everything from the soil preparation to the final harvesting methods. The journey from planting a single seed to harvesting the mature pod takes approximately four to five months, spanning 120 to 160 frost-free days depending on the variety and local climate.
From Seed to Flower: Initial Cultivation
Peanut cultivation begins with planting the shelled seed kernels after the last frost, typically from April through May in the United States Peanut Belt. Successful germination requires warm soil temperatures, ideally reaching 65°–70°F, as the plant is sensitive to cold conditions. Growers select light, well-drained, sandy loam soil, often with a slightly acidic to neutral pH between 5.5 and 7.0, because the developing pods need a loose medium to penetrate and expand.
Once the seed germinates, a seedling emerges within seven to ten days, growing into a low, leafy, herbaceous annual plant that spreads close to the ground. Like other legumes, the plant hosts symbiotic bacteria in its root nodules, allowing it to fix atmospheric nitrogen, which reduces the need for nitrogen-based fertilizers. About 40 days after planting, small, yellow, pea-like flowers begin to appear, mostly around the lower portion of the plant.
These flowers are self-pollinating and generally complete their fertilization process before the petals fall off. The plant continues its vegetative growth, producing new leaves and flowers continuously, which means it is indeterminate in its development. This prolonged flowering period ensures a steady supply of fertilized ovaries that will eventually mature into peanuts.
The Unique Process of Pegging
The moment of fertilization initiates the peanut’s distinct biological process: the formation of the “peg.” The peg is a specialized, stalk-like structure, technically a gynophore, that elongates rapidly from the base of the withered flower’s ovary. This embryonic fruit, encased within the sharp tip, is carried downward toward the soil surface.
The peg is driven to push itself into the ground, typically penetrating the soil to a depth of one to three inches. The soil must be loose and moist enough for the peg to successfully push through the surface and avoid being damaged. Pegs that remain above ground or are unable to penetrate the soil will fail to develop into mature pods.
The actual peanut pod, the fruit, only begins to mature once the peg tip has successfully buried itself in darkness, a process known as geocarpy. The developing pod also absorbs essential nutrients, particularly calcium, directly from the surrounding soil through the peg’s minute hairs. Pod formation and the subsequent filling of the kernels take an extended period, often requiring 60 to 70 days after the peg has entered the ground to reach full maturity.
Harvesting and Curing
Growers determine the optimal time for harvest by monitoring the color change of the inside of the peanut shell, which progresses from white to black as the pod matures. Harvesting too early results in low yields of immature kernels, while harvesting too late risks losing the peanuts as the pegs naturally begin to deteriorate and break.
The harvest is a two-step process, beginning with mechanical digging. A specialized machine cuts the main taproot below the level of the pods, lifting the entire plant out of the soil. The machine then immediately inverts the plant, leaving the peanuts attached to the vines, upside-down on the ground.
This inversion allows the peanuts to begin the first phase of drying, called “curing,” right in the field for two to four days. At the time of digging, the pods contain a high moisture content, often between 35% and 50%. This initial field curing reduces the moisture content to approximately 20%, which is necessary before the final mechanical harvesting step.
The second step involves a combine that separates the semi-dried pods from the vines, after which the peanuts are moved to commercial drying facilities to reduce the moisture content further, typically to 8.5% to 10.5%, for safe storage and to prevent mold growth.