The mung bean (Vigna radiata) is an annual legume known globally for its versatility, consumed as fresh sprouts or dried seeds. Originating in India, this warm-season crop thrives across Asia and other temperate and tropical regions. It is valued for its short growing cycle, typically ranging from 60 to 100 days from planting to harvest. The life of the mung bean plant is a rapid progression, moving from hydration to the final dry-down of the seed pod.
From Seed to Seedling Emergence
The journey begins with the seed taking up water in a process called imbibition, which reactivates the seed’s metabolic machinery. This initial phase is fast in mung beans, often lasting only a few hours as the seed absorbs water equal to its dry weight, causing it to swell significantly. Once conditions are right, the radicle (embryonic root) pushes through the seed coat and begins to anchor the plant in the soil.
The mung bean exhibits epigeal germination, meaning the cotyledons (seed leaves) are pulled above the soil surface by the elongation of the hypocotyl (embryonic stem). This emerging stem forms a distinct hook shape to protect the growing tip as it pushes through the soil. The cotyledons, now above ground, serve a dual function: providing the plant’s initial energy supply from stored food reserves and beginning rudimentary photosynthesis. This stage ends as the first true leaves begin to unfurl, signaling a shift to self-sufficiency.
Building Biomass: Vegetative Growth
The vegetative phase is characterized by the rapid accumulation of biomass, focusing on producing the photosynthetic machinery needed for later reproduction. The first pair of leaves to appear above the cotyledons are the unifoliate leaves, which are simple (having a single leaflet). These leaves quickly take over the bulk of the plant’s energy production.
Following the unifoliate leaves, all subsequent leaves are compound trifoliate leaves, defined by their characteristic three-leaflet structure. The development of these trifoliate leaves determines the plant’s vegetative stage, with each new node on the main stem producing another set. Lateral branching also begins, creating a bushier structure that increases the total leaf surface area for light capture. This growth is sustained by the plant’s ability, as a legume, to fix atmospheric nitrogen through a symbiotic relationship with specialized soil bacteria.
Flowering and Pod Setting
Flowering, the transition to the reproductive phase, typically begins 30 to 60 days after emergence, depending on the variety and environmental conditions. Mung bean flowers are small and usually pale yellow or greenish-yellow, appearing in dense clusters of up to 15 blooms at the leaf axils. This species is primarily self-pollinating, ensuring successful fertilization even with minimal insect activity.
The mung bean has an indeterminate flowering habit, meaning vegetative growth and flowering can occur simultaneously for an extended period, especially if soil moisture is maintained. As the flowers fade, the pods begin to set, developing into long, straight structures up to 5 inches in length. Initially, these pods are green and soft as the internal beans fill with moisture and nutrients. The pod-filling stage is a period of high water demand, during which the plant dedicates its energy reserves to seed development.
The Final Phase: Maturation and Harvest
The final stage involves the drying down of the plant and the physiological maturation of the seeds inside the pods. As the plant shifts its energy entirely to the seeds, the leaves often begin to yellow and senesce. The most obvious visual cue for maturity is the color change of the pods, which transition from green to a dark brown or black.
Pod desiccation is a gradual process; not all pods mature at once, so it is common to see flowers, green pods, and mature black pods on the same plant. For harvesting dry beans, the optimal time is when 85 to 90% of the pods have turned their dark, mature color to maximize yield and quality. Harvesting can involve hand-picking the mature pods, but for commercial production, the entire plant is often cut and allowed to dry further before the seeds are threshed out. Dried seeds should be stored only once their moisture content has reached approximately 12% to ensure long-term viability.