Corn, or maize, is one of the world’s most widely grown and important cereal crops, providing a major source of food, animal feed, and industrial products. Originating in ancient Mesoamerica, this tall annual grass has been selectively bred over thousands of years to produce the large, nutrient-dense kernels we rely on today. Its journey from a single seed to a mature, grain-filled stalk involves carefully timed biological stages.
Planting the Seed and Emergence
The corn plant’s life begins in the soil, requiring specific conditions for successful germination. The seed needs to absorb moisture equal to about 30% of its weight to initiate the embryo’s awakening. Planting should occur when soil temperatures reach a minimum of 50°F, although temperatures closer to 85°F to 90°F are considered optimal for rapid, uniform emergence.
Once the seed absorbs water, the first root, the radicle, grows downward, while the coleoptile, the protective sheath for the shoot, moves upward. The depth of planting is typically between 1.5 and 2.5 inches, a range that balances access to stable soil moisture with the energy required for the shoot to reach the surface.
The mesocotyl elongates to push the developing sprout through the soil toward the light. This emergence, often designated the V-E stage, establishes the seedling’s dependence on its seminal root system. Planting too shallow or too deep can disrupt this process, potentially leading to stunted growth or uneven stands.
Establishing the Vegetative Stalk
Following emergence, the corn plant enters a period of rapid vegetative growth, focusing on building the stalk, leaves, and structural roots. Agronomists track this phase using “V-stages,” which are counted by the number of fully unfurled leaves that display a visible leaf collar. In ideal conditions, a new leaf can unfurl every two to four days, and the plant develops approximately 20 leaves in total.
The initial primary and seminal roots are soon replaced by a more robust nodal root system. These nodal roots form from underground nodes, starting near the V3 stage, and become the main source of water and nutrient absorption. The growing point of the stalk remains safely below the soil surface until about the V6 stage, which is why young corn plants can often tolerate light frost or damage to the above-ground leaves.
During the mid-vegetative stages (V5 to V8), the maximum number of kernel rows on the developing ear is determined. The final height and overall leaf count of the mature corn plant are also established during this period of intensive growth. Brace roots, which emerge from nodes above the soil surface, provide additional structural support to anchor the tall stalk against wind.
Pollination and Fertilization
The transition from vegetative to reproductive growth marks the most sensitive period. The male flower, known as the tassel, emerges at the top of the stalk, and its appearance signifies the VT (tasseling) stage. Soon after, the reproductive phase officially begins with R1 (silking), defined by the first appearance of silks extending from the husks of the ear shoot.
Corn is a monoecious plant, meaning it has separate male and female flowers on the same plant, and it relies heavily on wind for cross-pollination. The tassel sheds millions of pollen grains, typically over a five to eight-day period. Each silk strand emerging from the ear is a style connected to a single potential kernel, or ovule.
For a kernel to develop, a pollen grain must land on a receptive silk, where it then germinates and grows a tube down the length of the silk to fertilize the ovule. Environmental stresses, such as high heat and drought, are particularly damaging during this period, often delaying silk emergence or causing pollen to lose viability, leading to barren spots on the ear.
Final Stages of Kernel Development
Once fertilization is complete, the process shifts to filling the kernels on the ear, moving through a series of reproductive stages focused on starch accumulation and moisture loss.
The R2 (Blister stage) is characterized by high moisture content and a kernel interior that resembles a small white blister. This quickly progresses to the R3 (Milk stage), about three weeks after silking, where the kernels contain a milky-white fluid, with a moisture content around 80%.
The fluid inside the kernel thickens to a pasty consistency during the R4 (Dough stage). The R5 (Dent stage) is named for the indentation that forms on the crown of the kernel as moisture decreases and the hard starch layer begins to form. This stage is tracked by the progression of the “milk line,” the visible boundary between the hard starch and the softer material, which moves toward the kernel’s base as it matures.
The final stage, R6, is Physiological Maturity, visually identified by the formation of the “black layer” at the base of the kernel where it attaches to the cob. This dark layer is an abscission zone that signals the cessation of nutrient flow into the kernel. At this point, the kernel has reached its maximum dry weight. While its moisture content is still relatively high (typically 30% to 35%), the growth phase is complete.