How Heat and Drought Affect Pollination

As we enter the hot humid days of summer, our corn crop is going through the critical process of pollination. In this article we’ll discuss some of the critical temperatures and moisture issues that can have an impact on pollination. Corn is a monoecious crop that relies on the flower pollinating the silks to complete the fertilization process. Each silk thread is attached to two kernels, and when the ovule is fertilized, kernel formation starts.


Timing is critical to the pollination process


Corn.The silk formation and emergence needs to be timed with the shedding of the pollen.  If all goes well in a corn field, the silks will begin to emerge from the husk 12-36 hours before the pollen grains start to fall. Pollen shed usually occurs over a 5-6 day period, providing a window of opportunity for the pollination process. If we miss “the nick,” the emergence of the silks and the timely shedding of pollen,  the pollination process will fail.

Silks can grow 1-2 inches per day under normal growing conditions, and will continue to grow for about 10 days or until they come in contact with a grain of pollen. Once the pollination process is complete, silk growth stops. Newly emerged silk has a pale green, translucent appearance. But once the silk is fertilized it rapidly changes color.



Factors affecting pollination


  • Rainfall – Heavy rainfall, or rainfall that lasts for several days, can wash the pollen off before it has a chance to fertilize the silk. The tassel emits pollen at two different times during the day, usually mid-morning and late in the day.


  • Drought – When you have a combination of low soil moisture and high temperatures which often causes more water to evaporate from the plant, silk growth is slowed. In times of extended dry conditions, silk growth can be reduced to near zero. Drought conditions affect silk development much more than pollen development. In extreme droughts, it is possible that the pollen grains have all fallen before the silks have emerged, resulting in a cob with only a few kernels developed.


  • High Temperatures – Long periods of high temperature can have a significant impact on the pollination process. Hot temperatures can inhibit the production and release of the pollen from the tassel. Silk tips can scorch under intense heat. If the silk tips scorch, it retards the ability of the silk tube to receive the pollen and the result will be two missing kernels on the cob. Temperatures above 85 degrees decrease the amount of pollen that is shed.

Corn.Under normal growing conditions, a grain of pollen can remain viable for up to 24 hours, but in hot dry conditions, that viability can be reduced to two hours or less. In temperatures of 100 degrees or more, the pollen may lose all viability before it has a chance to fertilize the silks. Even though drought can severely affect silk elongation, heat usually does not slow the silk’s growth.

Night-time temperatures are very important during this time of pollination. When the night temperatures fall below 75 degrees, the plant has a chance to recharge and refresh itself before another day of heat stress. If the nighttime temperatures do not drop below 85 degrees, it significantly increases the stress on the plant and risk of poor pollination.


Corn is a resilient plant and a marvel of creation. It’s ability to withstand heat and drought is remarkable. We’ve all seen crops that have endured a lot of stress and yet went on to yield a bountiful harvest. I hope your crop does well this season!