Corn, or Zea mays, is a widely grown crop used as food, livestock feed, and industrial products. The time it takes for a corn plant to fully grow is not fixed, as development is driven by genetics and environmental conditions. Generally, the period from planting to full maturity ranges from 60 to 120 days. Understanding the stages and environmental influences on this timeline is key to predicting when the crop will be ready.
The Overall Timeframe for Corn Maturity
The time required for corn to reach maturity is primarily determined by the specific variety planted. Early-maturing varieties are often ready in 60 to 80 days, while full-season hybrids can take 100 to 120 days or more.
A significant difference exists between the two main types of corn: sweet corn and field corn. Sweet corn, grown for human consumption, has a shorter growing period, typically reaching its ideal eating stage in 60 to 100 days. Field corn, used for animal feed, ethanol, and processed goods, requires a longer growing season to reach full physiological maturity, often needing 90 to 120 days or more.
The Distinct Stages of Corn Growth
The life cycle of a corn plant is divided into two main phases: the Vegetative (V) stages and the Reproductive (R) stages. The V stages focus on the plant’s structural development, starting with emergence (VE) and moving through successive leaf-collar stages (V1, V2, V3, etc.). During the early V stages, the plant relies on the seed’s energy reserves before transitioning to photosynthesis for all its energy needs, typically around the V3 stage.
This vegetative growth culminates with the tasseling stage (VT), where the male flower emerges at the top of the plant. The number of leaf stages before VT can vary widely, depending on the hybrid. The transition to the reproductive phase begins with silking (R1), where the female silks emerge from the ear shoot to catch pollen from the tassel.
Following pollination, the plant enters the kernel development stages. These begin with the blister (R2) and milk (R3) stages, marked by a clear and then milky liquid inside the kernels. The kernels then move to the dough (R4) and dent (R5) stages as the liquid thickens and a dent forms in the crown.
This reproductive phase, from silking (R1) to full maturity, generally takes about 55 to 65 days to complete.
Factors That Determine Growth Speed
The speed at which a corn plant moves through these stages is determined by the accumulation of heat, a measurement known as Growing Degree Days (GDD). GDD, or heat units, are calculated daily based on the maximum and minimum air temperatures, with a base temperature of 50°F and a maximum of 86°F. Corn development is stalled below 50°F and does not accelerate significantly above 86°F, making GDD a more accurate predictor of maturity than calendar days.
Each corn hybrid requires a specific, cumulative number of GDDs to reach its final physiological maturity. An early-maturing hybrid might need 2,000 to 2,400 GDDs, while a full-season variety may require 2,700 or more. This explains why a corn plant in a warm climate reaches maturity faster in terms of days than the same plant in a cooler region; the warmer climate accumulates the necessary GDDs more quickly.
The variety’s genetics also plays a significant role, as different hybrids are bred for early or late maturity. Environmental stressors, such as drought or nutrient deficiencies, can also slow the plant’s progress. Cold soil temperatures after planting can delay emergence (VE) for several weeks, significantly extending the overall time to maturity.
Indicators of Harvest Readiness
The final indicator of corn growth depends on the intended use of the crop. For field corn, the plant reaches its full physiological maturity at the R6 stage, which is visually confirmed by the formation of a “black layer” at the base of the kernel. This black layer indicates the kernel has reached its maximum dry weight and is no longer receiving nutrients from the plant.
For sweet corn, which is harvested for its sugar content, the readiness indicator is the R3 or milk stage. The optimal harvest time occurs about 19 to 23 days after the silks first appear. A practical test is to puncture a kernel with a thumbnail; if a milky white liquid squirts out, the corn is at its peak sweetness.
If the liquid is clear, the corn is not ready. If the liquid is thick and doughy, the corn has passed its prime eating window because the sugars have begun converting to starch. The silks on the ear are another visual cue; they should be brown and dry when the sweet corn is ready for picking.