The soybean, Glycine max, is a globally significant agricultural crop, valued for its protein and oil. As a legume, the plant possesses the unique ability to convert atmospheric nitrogen into a usable form, enriching the soil as it grows. The length of time it takes for a soybean plant to reach maturity and be ready for harvest is not fixed, but rather a variable timeline influenced by genetics, environment, and specific farming practices.
Total Growing Season Duration
The total time required for a soybean plant to progress from a newly planted seed to harvest maturity typically spans between 80 and 150 days. This wide range is governed by Maturity Groups (MGs), a classification system that assigns a number to a soybean variety based on its genetic predisposition to flower and mature. This system ranges from ultra-early groups (000) suited for northern latitudes with short growing seasons, up to groups VIII and IX for the longest seasons in sub-tropical regions.
A variety with a higher MG number requires a longer growing period before it begins the reproductive process of flowering and pod formation. For instance, varieties in Maturity Group 4, common in the mid-South, will take significantly longer to reach full maturity than Group 1 varieties grown in the northern Midwest. Moving up by one whole maturity group generally adds about ten days to the total time needed for the plant to mature.
Key Phases of Soybean Development
The overall growth timeline is broken down into two main periods: the Vegetative (V) stages and the Reproductive (R) stages, which often overlap. The initial phase begins shortly after planting, with the seedling typically emerging from the soil within five to ten days, depending on soil conditions. Throughout the V stages, the plant focuses on producing leaves and establishing a strong canopy, adding a new trifoliate leaf roughly every five days until it is ready to flower.
The transition to the reproductive stage, marked as R1 (beginning bloom), often starts around 40 to 60 days after planting, though this varies greatly by the Maturity Group. Flowering then progresses through R2 (full bloom), followed by R3 (beginning pod) and R4 (full pod), where the plant begins forming its yield. This pod and seed filling phase can last for four to six weeks.
The final stages involve the plant stopping its accumulation of dry matter at R7, which is termed physiological maturity. At this point, one normal pod on the main stem has reached its mature color. The final stage, R8 or full maturity, is reached when 95% of the pods on the plant have achieved their mature tan or brown color, and the plant is ready for mechanical harvest.
Environmental Influences on Growth Rate
Even within a specific Maturity Group, the actual time it takes to reach each stage can be accelerated or delayed by environmental conditions. Temperature plays a significant role in early development, as soybeans require warm soil, ideally around 60°F or higher, for quick and uniform emergence. Colder temperatures slow down the initial germination and emergence, which can add several days or even weeks to the start of the timeline.
Soybeans are considered short-day plants, meaning that shorter day lengths (or longer nights) signal the plant to begin flowering. This photoperiod sensitivity ensures that the plant begins its reproductive cycle early enough to complete seed fill before the first frost. Planting a variety too far north or south of its adapted region can drastically change the timeline.
Water availability impacts growth during the pod-filling stages (R3 to R6). Drought stress during this period can cause the plant to prematurely halt seed development and drop pods. Conversely, optimal temperature and moisture conditions can allow the plant to progress rapidly through its stages, maximizing the genetic potential of its Maturity Group.