Corn pollination is a critical time during the plant’s lifecycle as it plays a key role in determining yield.

The saying, “knee high by the 4th of July” does not hold as true as it once did. These days, most corn is head high by July and, in some cases, tasseling. Corn pollination is a critical time during the plant’s lifecycle as it plays a key role in determining yield. It’s important to note that corn plants are monoecious meaning they have both male and female reproductive parts. Let’s take a closer look at the reproductive process, the male and female parts involved, as well as potential pollination issues.

The female flower on a corn plant is the ear. Each silk is connected to an individual ovule on the ear and begins to elongate from that ovule 10 to 14 days prior to the R1 growth stage. Silk elongation begins at the base of the ear and continues to the tip. Therefore, the first emerging silks will be those connected to the ovules near the base of the ear. Complete silk emergence occurs within four to eight days after the first silks emerge from the husk. Once emerged, the silks remain receptive to pollen for up to 10 days.

During this time, pollen can land and germinate anywhere along the length of an exposed receptive silk. Within minutes of landing on silk, the pollen granule will germinate and grow a pollen tube down the length of the silk, connecting male genetic material to the ovule and allowing fertilization to be completed. Silks must be pollinated for each individual ovule to be fertilized and develop into a potential kernel. Typically, there are about 1,000 ovules on each ear, however, only about 400 to 600 will become kernels and survive to harvest.

The tassel is the male flower on a corn plant and is the last structure to emerge from the whorl. Each tassel has approximately 1,000 individual spikelets, each spikelet has two florets, and each floret contains three anthers. The anthers are structures that contain and control the release of pollen. 

Every hybrid varies, but on average an individual tassel produces approximately 6,000 pollen-bearing anthers. Pollen shed begins in the middle portion of the central tassel spike and progresses both upwards and downwards and then outwards across the branches of the tassel. During pollen shed, a yellow dust-like substance will fall from the tassel; there are millions of individual pollen grains released from the anthers.

Pollen shed starts in the middle of the main tassel and progresses up, down, and to additional branches.

It is difficult to estimate the total number of pollen grains produced by a tassel, but it is believed to be between two and 25 million. All pollen in an anther can be released within three minutes, however, the individual tassel can take up to seven days to finish shedding its pollen. 

Due to typical field variability and plant development, it can take an entire corn field as long as 14 days to completely shed all its pollen. Most pollen shed occurs mid-morning or late afternoon when temperatures are cool. If anthers are wet from heavy dew or rain, they will not open and release pollen. This is why you never have to worry about pollen being washed away during a rainstorm. Cool, humid temperatures tend to delay pollen shed, while hot, dry conditions can accelerate it, and extreme heat of 100°F or greater can kill pollen altogether.

The most common pollination issue is caused by severe drought and heat stress during silk emergence and pollen shed. This stress can reduce silk elongation, cause delays in silk timing, and increase pollen shed timing causing an unsynchronized pollination window. The result is scattered ovule fertilization or, in extreme cases, completely barren ears. 

Silk clipping from insects like rootworm beetles or Japanese beetles can also interfere with pollination. These insects feed on freshly emerged silks and can severely reduce the amount of receptive silk tissue exposed for pollen interception. This results in poor pollination, scattered fertilization, and missing kernels.


Nielsen, R.L. 2005. Silk emergence. Corny News Network, Purdue University. https://www.agry.purdue.edu/ext/corn/news/timeless/Silks.html.


Nielsen, R.L. 2005. Tassel emergence and pollen shed. Corny News Network, Purdue University. https://www.agry.purdue.edu/ext/corn/news/timeless/Tassels.html.