The peanut, often incorrectly called a nut, is actually a legume that develops its pods underground. The entire growing season, from planting until harvest, generally spans four to five months. This translates to approximately 120 to 150 days of growth, depending on the specific variety and local climate conditions. Understanding the distinct phases of this growth cycle is key to appreciating how the peanut transitions from a small seed to a mature, edible product.
Overall Duration and Environmental Requirements
The total time a peanut needs to grow is heavily influenced by the chosen variety and the environment. Varieties like Spanish peanuts mature relatively quickly, often requiring only 90 to 120 days until harvest. Conversely, the larger Virginia and Runner types, widely grown for snacking and peanut butter, typically need 130 to 150 days to fully develop.
The crop requires consistent warmth and sunshine to complete its cycle. Planting must occur after the last frost, specifically when the soil temperature reaches a minimum of 65°F, ideally sustained at 68°F to 70°F. Cooler soil temperatures can significantly delay germination and seedling emergence, extending the time to maturity.
The preferred soil type is a loose, sandy loam, which accommodates the plant’s reproductive process. This loose texture allows the developing pods to easily push into the ground and expand. If the soil is too heavy or compacted, the growth cycle can be prolonged, or the plant may fail to produce a full harvest.
Key Growth Stages: From Flower to Peg
The peanut plant begins its life cycle with vegetative growth, sprouting about 10 days after planting and developing leaves and stems for the first 30 to 40 days. Once this canopy is established, the plant starts to produce small, yellow, self-pollinating flowers, usually around 40 to 55 days after planting. The flowers are borne above ground, but the fruit develops below the soil surface, a process known as geocarpy.
After the flower is fertilized, a structure called a “peg,” or gynophore, forms from the base of the former flower. This peg is a fertilized ovary that elongates and senses gravity, causing it to curve downward toward the earth. It then pushes into the soil, growing one to three inches deep.
The peg must successfully penetrate the soil for the peanut pod to form. Once buried, the tip swells and turns horizontal, and the embryo begins to mature into a peanut pod. This underground development phase, where the pod fills with the kernel, is the final stage of growth, typically requiring consistent moisture and warmth for 60 to 110 days after planting.
Determining Maturity and Harvesting
The end of the 120- to 150-day cycle is marked by specific physiological changes, not a simple calendar date. A visual indicator that the peanuts are nearing readiness is the yellowing and wilting of the leaves. However, because the plant is indeterminate (it continues to flower and set new pods while older ones mature), a precise assessment is necessary.
To determine the optimal harvest time, growers must physically sample the underground pods. This involves digging up a few plants and scraping away the outer layer of the shell (the mesocarp) to reveal its internal color. The shell interior changes color in a predictable sequence as the pod matures, progressing from white, to yellow, to orange, and finally to brown and black.
The goal is to harvest when a significant percentage of the pods (often 70% or more) have reached the mature brown or black color classes. Once maturity is confirmed, the peanuts are harvested using specialized equipment to dig up the entire plant and invert it, leaving the pods exposed to the air. The newly harvested peanuts are left in the field for a few days to cure, or dry, which is required for proper storage and edibility.