The Basics of Ear Formation and Kernel Development

Ear development begins during the vegetative stages, starting around the V5 to V6 growth stages. Tassel initiation is also starting during this time. The number of rows around is determined shortly after ear initiation, between V5 to V7 (Abendroth et al. 2011). The typical range for most hybrids for row number is between 14 to 18. Row number develops in even numbers, unless some stress has occurred to that plant. While row number is highly related to genetics and less by the environment, stresses during this window can affect row number. Keep in mind that stress prior to the V5 to V7 window has NO direct bearing on ear size, unless that stress resulted in severely stunted plants.

After the plant has determined row number, it will next determine row length or the number of ovules per row. This occurs over a much longer time period, starting around V5 to V7 and it isn’t finalized until V12 to V17, depending upon the hybrid. Severe stress from V5 to V12 can interfere more with the ear length or ovules per row rather than the number or rows per ear.

Once the ear size has been determined, the next critical period is what happens in the early reproductive stages related to pollination and fertilization for kernel development. We often take this process for granted and just expect it happens.

Pollination is the movement of pollen from the tassel to the silks coming from the ears. Each ovule (potential kernel) on an ear has its own silk. Fertilization is the actual union of the male and female gametes after the pollen tube reaches the ovule. Good kernel set (how many kernels develop on the ear) requires both successful pollination and fertilization. Historically, tassels typically emerged before silks. However, more recently hybrids have more synchronized tassel and silk emergence, or in some cases silks may emerge prior to tassels emergence. 

Silk elongation stops after pollen has been captured by that silk. If silks remain unpollinated, they will continue to elongate for up to 10 days after they first emerge and remain receptive to pollen during this time. However, their receptivity to pollen is the highest during the first 3 to 5 days after emergence and starts to decline after day 5. Unusually long silks can be a clue that an ear may not have successfully pollinated. 

Read more on the pollination and fertilization process in corn in the following articles:  

• Tassel Emergence and Pollen Shed, Bob Nielson, Purdue University 
• Silk Development and Emergence in Corn, Bob Nielson, Purdue University 

After kernels have been fertilized, the plant will begin filling those kernels. If there are stresses early in the grain fill period, plants may abort some kernels. These stresses may include severe drought stress, excessive heat stress, nutrient deficiencies (mostly nitrogen), or extensive loss of green tissue due to disease (i.e. Southern Rust in 2025) or hail. This typically happens within the first two weeks of pollination. This is often observed on the kernels closer to the ear tip since they are the last to be fertilized. Once corn reaches the R3 (milk) stage, yield loss can occur from reductions in kernel weight. 

Resources: 

Abendroth, L. J., Elmore, R. W., Boyer, M. J., & Marlay, S. K. (2011). Corn growth and development (PMR 1009). Iowa State University Extension, Ames, IA. https://shop.iastate.edu/extension/farm-environment/crops-and-soils/agr… [URL accessed August 10, 2026]