Peanuts, botanically classified as legumes, possess a distinctive growth cycle. Understanding these developmental stages is useful for successful cultivation and maximizing yield. Unlike typical legumes that form pods above ground, peanuts exhibit a unique underground fruiting habit, requiring specific environmental conditions and management practices.
The Unique Peanut Growth Habit
The defining characteristic of peanuts is their geocarpic nature, meaning their fruits develop beneath the soil surface. After fertilization of the above-ground flowers, a specialized structure called a “peg” or gynophore emerges from the withered flower. This peg is an elongated, thread-like stalk that grows downwards, actively pushing into the soil. The tip of this peg contains the developing ovary, which, once buried, begins to swell and form the peanut pod. This underground development protects the nascent pods from various environmental stressors and is an adaptation for the plant’s reproduction.
Germination and Early Vegetative Growth
The peanut life cycle begins with planting the seed. For successful germination, soil temperatures need to be at least 65°F (18°C). Upon absorbing water, the seed swells, and the embryo within begins to grow. The primary root, or radicle, emerges first, anchoring the seedling in the soil, followed by the plumule, which develops into the shoot and leaves. This emergence, often called “ground cracking,” occurs about 7 to 14 days after planting. During this early vegetative phase, the plant focuses on establishing its root system and producing leaves and stems above ground.
Flowering and Pegging
Approximately 30 to 40 days after emergence, peanut plants begin to produce small, yellow, pea-like flowers, primarily in the leaf axils of their branches. These flowers are self-pollinating, meaning they do not rely on external agents like bees or wind for fertilization. The petals fold together, and fertilization occurs within a few hours.
Following successful pollination, the petals wither, and the fertilized ovary at the base of the flower begins to elongate, forming the “peg.” This peg grows downwards, exhibiting positive gravitropism, and penetrates the soil within about 10 to 14 days after pollination. Loose, moist soil and adequate calcium in the pegging zone are important for successful peg penetration and subsequent pod formation.
Pod Development and Maturation
Once the peg successfully enters the soil, the embryo at its tip, which had its growth arrested, resumes development. The tip of the peg swells to form the peanut pod, which then undergoes significant enlargement and kernel filling. Within the pod, the seeds develop, accumulating oils and nutrients. The shell hardens, and the characteristic flavor of the peanut forms during this maturation. The perception of darkness and mechanical pressure from the surrounding soil are important signals for the transformation of the peg into a mature pod.
Harvesting and Curing Considerations
Harvesting signals the culmination of the peanut’s growth cycle, occurring 120 to 160 days after planting, depending on the variety. Indicators for harvest readiness include the yellowing of the plant’s foliage and the maturation of the pods themselves, which turn from green to yellow or brown. Farmers often dig up sample plants to visually inspect the pods for fullness and shell color.
After digging, the peanut plants are left in windrows in the field for a period of “curing” or initial drying. This post-harvest step reduces the moisture content of the peanuts from 35-50% down to 8-10%, which prevents mold, enhances flavor, and prepares them for storage. Proper curing ensures the quality and storability of the final product.