Corn is wind pollinated and is pollinated when wind blows pollen from the male flower, the tassel, onto the female flower, the silk on the ear. This means that corn can self-pollinate, but within a field of corn, 97% of pollination is done by neighboring plants.
Gardeners are recommended to grow blocks of corn with more short rows as opposed to one or two long rows so the pollen has a better chance of successfully pollinating the silks.
Each piece of silk if pollinated will become one kernel of corn. If pollination is poor we end up with ears of corn with patches of kernels missing.
The number of rows on a cob is determined early in the plants life cycle when the cob starts to form and this number will always be even. While the number of rows is set early the ear will grow bigger and produce more kernels in each row with favorable growing conditions.
Corn is what is known as monoecious, meaning one plant has both a male and female flower. The male flower is the tassel at the top of the corn plant. You can see what’s called anthers hanging from the tassel, they look like two pieces of rice stuck together. Inside each anther is anywhere from 2 to 25 million pieces of pollen.
After being released from the anther the pollen is only viable for a few minutes to up to 2 hours before it drys out. This depends mainly on temperature. Most pollen travels about 50 feet but a 15 MPH wind is capable of blowing a piece of pollen up to 1/2 a mile.
The anthers on one tassel will take around 7 days to release all of their pollen, with the greatest release of pollen occurring on the 2nd or 3rd day of anther appearance. The tassels appear at different times on corn throughout the field and a typical field will have about 14 days of pollen shed.
The female flower is the ear with the silk. A piece of pollen can come into contact with a piece of silk at any location on the silk. The silk has small hairs call trichomes that help to catch the pollen.
After contact with silk, pollen will develop a tube inside the silk and deliver its male genetic material to the ovary at the base of the silk within 24 hours resulting in successful pollination of that piece of silk.
Typically around 1,000 pieces of silk per ear will exist and somewhere between 400-600 kernels will form. Silks begin growing from the base of the corn cob and grow from the tips of the cob last.
Corn silks can grow 1.5″ a day. Viable silks are present for around 14 days and emerge shortly after pollen starts to be released. If silk is cut by insects feeding on them they will regrow.
How Does Corn Reproduce?
Corn reproduces when a piece of pollen from a tassel lands on a piece of silk protruding from an ear. Each piece of silk that’s successfully pollinated creates a kernel. Every kernel is a seed that when planted can turn into 300-1000 more kernels per cob on the new plant.
When a piece of pollen lands on a piece of silk it produces a pollen tube and within 24 hours reaches the egg at the base of the silk where the silk meets the cob. This results in successful pollination and the fertilized egg develops into a kernel.
Weather & Corn Pollination
Anthers will not open and release pollen if they’re wet. This is why the main release of pollen happens early in the mornings after the morning dew drys. Cold wet days delay the release of pollen and warm dry days speed up the release of pollen.
Temperatures over 95 degrees Fahrenheit will kill pollen. This high temperature will cause the pollen to dry out immediately before the pollen has a chance to pollinate any silks.
Two characteristics of the pollen release safeguard the pollination process. Firstly pollen is released the most in the early morning before high temperatures. Second, pollen is released on different days throughout a field with one tassel taking around 7 days to release its pollen.
Corn Cross Pollination
Cross pollination usually occurs between plants in the same family. For example, a pumpkin could cross pollinate a zucchini. The result would be a normal zucchini but the seeds in that zucchini would produce a plant that would be a mix of pumpkin and zucchini. This is how cross pollination affects most plants with the seed being the cross.
Corn is different and when cross pollination occurs, let’s say between a sweet corn variety and popcorn variety, the result will be a cob of corn with kernels from both variety. The popcorn kernels will be tough and not sweet making the cob of corn not enjoyable as sweet corn.
There are three ways to avoid cross pollination of corn varieties.
The best method to avoid cross pollination in corn is using hand pollination and putting bags over the ears before silks appear to prevent pollination of the silks. Remove the bag to hand fertilize with pollen from the variety you want to pollinate with and then replace the bag to prevent any pollen from different varieties getting to the silk of that corn.
The next method is not available to most gardeners and that is to plant the corn varieties far from each other at least 300 feet. It’s very helpful to have physical barriers between the two fields like woods.
The last method is to plant varieties that mature at different times and will shed pollen at different times. It’s suggested to have at least a two week difference in maturity dates so planting an early maturing variety and a late maturing variety should do the trick.
GMO corn cross pollination is a real problem for open field growers or anybody trying to grow non-GMO seed corn in the midwest or anywhere else near commercial corn fields.
This article shows how growers of a blue corn variety planted their field 2,000 feet away from commercial fields and still found some cross pollination.
Fortunately these corn growers were growing a blue variety and they could tell what kernels were cross-pollinated because those kernels were yellow and stuck out on the cob full of blue corn.
The cross pollination was very low but if the corn seed they were growing would have been yellow and they couldn’t distinguish which kernels had been cross pollinated it would have created a major problem.
If this was the case the seed corn planted the next year with that small percent of genetics from the cross pollination would balloon as that small percentage would have been planted randomly throughout the field and pollinated corn all around them.
Corn Pollination Bees
Bees love corn pollen. They can be seen working hard on tassels carrying bushels of corn pollen back to their hive. But they have little use for the silks and don’t give them much attention.
Corn is wind pollinated and does not depend on insects to spread its pollen. You could say they play a very tiny role by moving tassels around and incidentally spreading some pollen but really they don’t do much for corn pollination.
Here is a 57 page paper from Iowa State University that describes the role of insects in Iowa corn and soybean fields. Corn is wind pollinated and soybeans are self-pollinated, neither depend on insects for pollination.
How To Hand Pollinate Corn
Most pollen is released in the early morning so this is the best time to collect the pollen. You can hold a tray and tap or shake the top of the plant just below the tassel and pollen will be spread in the air and land on the tray.
Another method is to cut off a branch of the tassel filled with anthers or an entire tassel and rub the tassel along the silks of the ears. For best results, do this process every day for a week or two.
Corn Pollination Bags
Here are two links to native seeds that sell bags for tassels as well as for the ear shoots. The tassel bags go around the tassel and are used to catch the pollen inside the bag to hand pollinate with.
The ear shoot bag is to cover the silks from pollen until you’re ready to hand pollinate it with the pollen from the variety you want.
Neither of these come with ties so here’s a link to cheap plastic garden tie you can use for whatever in the garden. I prefer this plastic type tie because it can stretch and doesn’t get into a knot like the garden tie on a spool that looks like fishing line. That type always knots up on me and I have a job to take it off the spool and untangle it.
I hope you enjoyed the article and please share any thoughts you have on corn pollination below.