Soybeans are a globally important crop used for food, feed, and oil. Determining the time required for maturity is complex, as the total duration from planting to harvest can vary dramatically, ranging from 75 to over 200 days. A common range for many varieties is 90 to 150 days. Understanding the timeline requires looking beyond a single fixed number and examining the plant’s programmed life stages and external influences.
The Soybean Growth Cycle
The soybean plant’s life is divided into two distinct phases: the Vegetative (V) stages and the Reproductive (R) stages. The V-stages focus on developing leaves, stems, and roots, building the plant’s structure and capacity for photosynthesis. These stages are designated by the number of fully developed trifoliolate leaves present on the main stem (e.g., V1, V2).
The Reproductive stages begin with flowering (R1) and continue through pod and seed development. This phase determines the final duration of the crop, as the plant shifts energy from producing leaves to filling pods with mature seeds. The ultimate goal is R8, or Full Maturity, which breeders use to classify a variety’s overall growth period.
Understanding Maturity Groups
The most significant factor influencing maturity time is the Maturity Group (MG) classification. This system categorizes varieties based on their genetic response to photoperiod, or day length. Soybeans are short-day plants, triggered to flower when days shorten to a specific length. Breeders use a system of 13 MGs, from 000 (earliest) to X (latest), to match varieties to suitable growing latitudes.
Lower-numbered MGs (000 through III) are adapted to northern latitudes with shorter growing seasons and earlier frosts. These varieties mature quickly, often in 90 to 120 days, due to a shorter vegetative period before flowering. Higher-numbered groups (VII through X) are suited for southern regions closer to the equator, where the growing season is longer, allowing for slower maturation. The difference in maturity date between two adjacent, whole-numbered MGs is generally 10 to 15 days.
Growers select an MG to maximize the growth period while ensuring the plant reaches R7, or physiological maturity, before the first killing frost. Selecting a longer MG than typical for a region can increase yield potential but raises the risk of frost damage. Conversely, selecting a shorter MG allows for earlier harvest but may limit overall growth and yield potential.
Climate and Environmental Factors
While the Maturity Group provides the genetic blueprint, external environmental factors can accelerate or delay maturity. Temperature and water availability are the primary variables interacting with the plant’s internal clock. High temperatures, especially during the reproductive stages, can significantly accelerate maturation, shortening the overall growth period.
Below-normal temperatures during the growing season slow development, delaying flowering and final maturity. Stressors like drought or extreme heat during the pod-filling stages (R3 to R6) can force premature maturity, resulting in lower yields because seeds do not fully develop. Adequate rainfall and moderate temperatures allow the plant to proceed on its programmed schedule.
The planting date also affects the plant’s perception of day length. Planting a variety later than recommended may dramatically shorten the vegetative phase, as the photoperiod cue for flowering arrives sooner. This can lead to a smaller plant size at maturity, requiring farmers to adjust the Maturity Group selection for late plantings to avoid fall frost damage.
Visual Cues for Harvesting Time
Full maturity, R8, is visually defined when 95% of the pods have reached their mature color, typically brown or tan. This stage follows R7, or physiological maturity, where the seed has reached its maximum dry weight. At R7, the seed moisture content is high, approximately 60%.
Once the plant reaches R8, the leaves have usually dropped, and the seeds begin the crucial dry-down phase. The period between R8 and harvest is not part of the biological maturity cycle but is a drying period. The optimal moisture content for harvest is generally between 13% and 15% to minimize mechanical damage and storage issues.
This drying process typically requires an additional 5 to 20 days of favorable weather after R8, depending on atmospheric conditions like temperature, wind, and humidity. Harvesting too early (above 15% moisture) can lead to storage problems. Harvesting too late (below 11% moisture) increases the risk of pod shatter and yield loss.