The corn ear is the reproductive structure containing the kernels people eat. Its appearance marks the plant’s shift from focusing on growth to focusing on reproduction. The timeline for when the ear becomes visible outside the husk is highly variable, depending on the corn variety and the growing environment. The external emergence of the silk is the defining moment when the plant transitions from the rapid vegetative phase to the critical reproductive phase, committing resources to producing harvestable grain.
The Vegetative Phase: Preparing for Ear Development
The physical appearance of the ear is preceded by an intense period of leaf and stalk growth designed to build the capacity for grain production. During the vegetative stages, the plant maximizes photosynthesis, creating the energy reserves needed to fill the eventual ear. The ear structure, or ear primordia, is initiated very early, usually around the V5 or V6 stage when the plant has five or six visible leaf collars.
At this early stage, the tiny, undeveloped ear is hidden inside the stalk, but its size potential, including the number of kernel rows, is being determined. The developing stalk and leaves supply the necessary sugars for kernel development later on. Proper nutrient and water management during this time is important, because stress may limit the potential number of kernels before the ear is even visible outside the plant.
The Reproductive Phase: Identifying Ear Appearance and Silking
The first easily identifiable sign that the ear has fully developed internally and is ready for pollination is the emergence of the silks, marking the R1 or silking stage. Silks are the female flower parts, and one silk grows from each potential kernel on the ear. For many common varieties, this stage typically occurs about 55 to 75 days after the plant has emerged from the soil, though this timeframe can vary widely.
The silk strands must emerge from the husk leaves to catch the pollen that falls from the tassel, the male flower located at the very top of the plant. The tassel usually emerges a few days before the silks appear, a process known as tasseling (VT stage). Successful pollination requires that the silks and pollen shed occur at roughly the same time, allowing the pollen to travel down the silk tube to fertilize the ovule, which then develops into a kernel.
Key Factors Controlling Development Speed
The speed at which a corn plant progresses toward the silking stage is primarily governed by temperature, measured using Growing Degree Days (GDD) or heat units. GDD accounts for the fact that corn development accelerates in warmer weather and slows down in cooler conditions. The calculation uses a base temperature of 50°F, below which growth stops, and caps the maximum temperature at 86°F, where growth rates plateau.
Different corn varieties have specific genetic requirements for GDD accumulation to reach silking, making the calendar day range highly variable. Early-maturing varieties require fewer GDD units than full-season varieties. Environmental factors, such as drought or excessive heat during the vegetative stages, can also affect the plant’s ability to transition smoothly into the reproductive phase.
Maturation: From Ear Appearance to Harvest
Once the ear has appeared and the silks have been pollinated, the plant enters the grain fill period, focusing energy on kernel development through several reproductive stages (R2 to R6). The first stage after silking is the blister stage (R2), occurring about 10 to 14 days later, where kernels are white and filled with a clear liquid. This is followed by the milk stage (R3), where the liquid inside the kernels turns milky white due to rapid starch accumulation.
Next is the dough stage (R4), when the milky fluid thickens to a paste-like consistency, and the kernels begin to accumulate half of their dry weight. The dent stage (R5) is marked by a dent forming at the top of the kernel as moisture content drops. The final stage, physiological maturity (R6), is reached when a dark layer, called the black layer, forms at the base of the kernel, signifying the grain has attained its maximum dry weight and is ready for harvest.