The soybean, Glycine max, is a globally important crop. The time required for a soybean plant to complete its full life cycle, from planting to harvest readiness, typically ranges from 90 to 150 days. This wide timeline depends heavily on the specific genetic variety planted and the environmental conditions of the growing season. Understanding this timeline requires recognizing that the plant’s development progresses through distinct biological phases.
The Typical Life Cycle Duration
The total period from the emergence of the seedling to maturation is categorized into two major developmental phases. The first is the Vegetative (V) stage, which focuses on the growth of leaves, stems, and roots, building the plant’s structure. This is followed by the Reproductive (R) stage, which involves flowering, pod development, and seed fill.
Early-season varieties, often grown in northern latitudes, may complete their cycle in as little as three months. In contrast, late-season varieties, common in warmer, southern climates, may require up to five months to reach full maturity. The specific number of days is governed by the transition from the V to R stages, which acts as a biological trigger setting the pace for the remainder of the plant’s life.
Key Vegetative and Reproductive Stages
The initial Vegetative stages (V-stages) are marked by the number of fully developed trifoliolate leaves on the main stem. This phase establishes the plant’s photosynthetic capacity, with new leaf nodes appearing sequentially as the plant grows taller. The duration of this phase directly influences the plant’s size and its capacity to produce pods and seeds later in the season.
The transition to the Reproductive stages (R-stages) begins with R1, or beginning bloom, when the first flower appears on the main stem. Pod development begins at R3, and pods reach their full size at the R4 stage, marking the start of intensive resource allocation. The R5 stage, known as beginning seed, is initiated when the seed inside an upper node pod reaches a specific length, signaling the start of rapid dry weight accumulation.
Seed filling continues through the R6, or full seed, stage, where the seeds fully occupy the pod cavity and accumulate nutrients. This period from R5 to R6 is when the plant is most sensitive to environmental stress, as the seed is actively gaining mass. Each stage represents a measurable benchmark of the plant’s development.
How Variety and Environment Affect Timing
The most significant factor determining the overall growth duration is the variety’s genetic classification, known as its Maturity Group (MG). The MG system ranges from 000 for the earliest maturing varieties to IX for the latest, with approximately five to seven days between each whole number group. Farmers select a specific MG based on the length of their region’s growing season to ensure the crop matures before the first killing frost.
Soybeans are sensitive to photoperiod, or day length, which acts as the primary signal for initiating the reproductive phase. A chemical compound in the leaves responds to the duration of darkness and triggers the plant to switch from vegetative growth to flowering. This explains why a specific variety matures at different times when planted in different latitudes, as day length varies by geographic location.
Temperature also modifies the timeline, as soybeans require a specific accumulation of heat units, referred to as Growing Degree Days (GDDs), to progress through their stages. Warmer temperatures accelerate the accumulation of these units, leading to faster progression. Conversely, cooler conditions slow the plant’s metabolism, extending the time needed to reach each subsequent stage.
Signs of Maturity and Harvest Timing
The end of the growth period is defined by two distinct stages: physiological maturity and harvest readiness. Physiological maturity is reached at the R7 stage, which is visually marked when one normal pod on the main stem achieves its mature color, typically brown or tan. At this point, the seed has reached its maximum dry weight, and the plant ceases to accumulate further mass.
The plant begins to shed its leaves as the seeds lose their green color. The next stage, R8, or full maturity, occurs when 95% of the pods have reached their mature color. While the seed is biologically mature at R7, its moisture content is still too high for safe storage.
Harvest timing is determined by the environmental dry-down period that follows R8. The seeds must naturally dry in the field to a moisture content suitable for storage, often around 13 to 14%. This final dry-down process usually requires an additional five to ten days of warm, dry weather after the R8 stage to achieve harvest readiness.