Corn (maize) is an annual crop whose life cycle is precisely divided into distinct vegetative and reproductive phases. The question of when it starts to grow ears is directly related to the shift from building plant structure to forming the grain. This transition marks the period where the plant’s focus moves from producing leaves and roots to the visible appearance and development of its fruit. Understanding this process requires tracking the sequential stages of growth, which are classified using an agricultural numbering system.
Understanding Corn’s Vegetative Stages
The initial growth period for corn is the vegetative phase, labeled with a ‘V’ followed by the number of fully developed leaf collars. The plant begins at emergence (VE) and progresses through stages like V1, V3, and V10, focusing on leaf and stalk production to establish its eventual height and size. Although no ear is externally visible yet, the internal structure of the primary ear is determined surprisingly early in the plant’s life. The number of potential kernel rows is set between the V5 and V7 stages. This initial phase of structural growth typically lasts for about 45 to 60 days, depending on the corn variety and the local climate conditions.
Tasseling and Silking: The Start of Ear Growth
The actual, visible start of ear growth is marked by the onset of the reproductive phase, beginning with the emergence of the tassel and silks. The tassel, the male flower, appears first at the top of the stalk, defining the VT (Tasseling) stage. Shortly after the tassel is fully extended, the female flowers begin to emerge from the ear shoots as fine strands called silks.
The first reproductive stage, R1 (Silking), occurs when these silks become visible outside the husk. Silking generally happens about 60 to 75 days after the plant emerges, or once the plant has reached its full height. Each individual silk strand must catch a pollen grain from the tassel for a kernel to develop at that spot on the ear.
Successful pollination during this narrow window is important for producing a viable ear. Silks remain receptive to pollen for about 10 days, and moisture stress during this period can severely reduce the number of kernels that form. Once a silk is pollinated, it detaches and dries.
Measuring Growth: The Role of Growing Degree Days
The timing of corn growth stages, including when silking begins, cannot be reliably predicted by calendar days alone. Temperature plays a dominant role, which is why agricultural experts use a measurement called Growing Degree Days (GDD), or heat units, to track development. GDD is an accumulation of heat above a base temperature, which for corn is typically 50 degrees Fahrenheit, as the plant does not grow below this point.
This measurement provides a more accurate physiological estimate of the plant’s progress than simply counting days. Seed companies use GDD to assign maturity ratings to specific corn varieties, indicating the total number of heat units required to reach physiological maturity. By tracking the accumulated GDD in their fields, farmers can accurately forecast when their corn will reach key milestones, such as tasseling and silking.
Ear Fill and Maturity
Once the ear is pollinated, the plant enters the final stages of physical development and maturation, known collectively as ear fill. The first stage after silking is R2 (Blister), where the kernels are white, contain clear fluid, and resemble small blisters. This is quickly followed by R3 (Milk), where the fluid inside the kernels turns milky-white and sugary, marking the stage when sweet corn is often harvested.
The kernels continue to mature through R4 (Dough), where the milky liquid thickens to a pasty consistency as starch accumulates. Next is R5 (Dent), where the kernels begin to dry and a dent forms in the crown of the kernel.
The final stage, R6 (Physiological Maturity), occurs when a brown or black layer forms at the tip of the kernel where it attaches to the cob. This “black layer” signifies that the ear is finished growing and has reached its maximum dry weight, typically containing 30 to 35 percent moisture.