Sorghum (\(Sorghum\ bicolor\)) is a resilient crop known for its ability to thrive in hot, arid conditions where other cereals often fail. This ancient grain, one of the world’s most important cereal crops, is cultivated globally for grain, forage, and biofuel production. Its robust nature makes it highly tolerant of drought and heat, but its growth timeline is a dynamic process influenced by genetics and environment. Understanding the duration of its development is crucial for successful cultivation and timely harvest.
Overall Time to Maturity
The total time it takes for sorghum to grow from planting to harvestable maturity typically falls within a range of 100 to 140 days. This duration is highly dependent on the specific type of sorghum being grown and the intended use of the crop. Grain sorghum, grown for its seed, is harvested once the kernels reach physiological maturity, which usually takes approximately 115 to 140 days. Physiological maturity is signified by the formation of the “black layer” at the base of the seed, indicating maximum dry weight accumulation. Conversely, forage or silage sorghum, harvested for animal feed, is often cut much earlier to maximize nutritional quality, generally when the grain is in the soft dough stage (70 to 90 days after planting).
Key Stages of Sorghum Development
The sorghum plant follows a predictable pattern of development, divided into vegetative (V) and reproductive (R) phases, driven largely by temperature accumulation. The initial phase is emergence and seedling establishment, where the shoot breaks through the soil surface, typically three to ten days after planting. During this time, the growing point remains safely below the soil line, and the plant is counted by the number of leaves that have visible collars.
The vegetative development stage involves rapid stem and leaf production, culminating in growing point differentiation (GPD). This transition, where the plant switches from producing leaves to forming the seed head, usually occurs about 30 days after emergence. After this, the potential number of seeds per head is determined. The most intense period of growth follows this stage, with the plant forming its full canopy and maximizing light interception.
The reproductive phase begins with the boot stage, where the developing seed head, or panicle, is fully enclosed within the flag leaf sheath. This is quickly followed by heading and flowering, where the panicle emerges from the sheath and begins to bloom. Many modern hybrids typically reach the half-bloom stage (50% of the heads flowering) between 55 and 80 days after planting. The final stage is grain fill and maturation, which progresses from the milk stage to the soft dough, hard dough, and finally physiological maturity. This entire period from flowering to the hard dough stage takes approximately 25 to 45 days.
Factors Influencing Growth Speed
The variability in the sorghum timeline is primarily a function of the specific hybrid selected and the environmental conditions encountered throughout the season.
Hybrid Selection
Hybrid selection is the most controllable factor, as seed companies classify varieties based on their relative maturity. This classification often correlates to the number of days required to reach half-bloom. Early-maturing hybrids may flower in as few as 52 days, while late-maturing types may take 62 days or more to reach the same stage, directly affecting the final harvest date.
Temperature
Temperature is the primary environmental driver of growth, as sorghum development is directly related to the accumulation of heat units, known as Growing Degree Units (GDU). While sorghum is warm-weather tolerant, with an optimal growth temperature of 27 to 30 ºC, cooler temperatures slow the rate of development significantly. A medium-maturity hybrid planted in a cooler period might take 80 days to flower, while the same hybrid planted later in the season may reach flowering in only 60 days.
Moisture Availability
Moisture availability also plays a significant role in determining how quickly the plant progresses through its life cycle. Although sorghum is known for its drought tolerance, severe moisture stress during key reproductive phases, particularly from the boot stage through flowering, can slow development and negatively impact seed set. The plant’s ability to extract water from the soil helps it mitigate short-term drought, but prolonged stress can delay or stunt the progress toward maturity.