How To Avoid Corn Cross Pollination

I often get questions about planting corn and corn cross pollination.  I’d always been taught that you had to be careful with corn, but for years I didn’t really know the “why”.

Corn Cross Pollination

First let’s talk about what corn cross pollination is and why it is such a worry.  Cross pollination is the natural process where pollen from one variety of a plant pollinates the flower of another.

Cross pollination usually only effects plants within the same family (to learn more about plant families read this post).  So for example a zucchini can cross pollinate with a pumpkin, but the results of the cross pollination will not show up until the next generation.  So it will be the off spring of the cross pollination that will be a new plant.  You will NOT get a pumkinzini this year.

Anyone that says their (x) crossed with (X) and I got this weird funky fruit is mistaken.  In those cases what really happened is they started out with bad seed or there was some environmental factor that made this years fruit “funky”.  Strange fruit in this year, is not the result of cross pollination this year.  I repeat, cross pollination affects the next generations fruit, not this years fruit in almost all families of veggies that can cross pollinate.

BUT, corn cross pollination in an exception to that rule.  The corn that you get this year, can and will be affected by cross pollination.  So you have to be careful what types of corn you plant in your garden.

It all has to do with Dominant Genes.

Field corn and Popcorn are always dominate to sweet corn.

Also regular old sweet corn (or even heirloom sweet corn) may be dominate to many of the “super sweet” varieties of corn out there on the market.

So what does this mean to the home gardener?

Corn is wind pollinated, which means the pollen is spread almost exclusively by the wind (No Insects Involved).

Corn Cross Pollination 2

Corn plants are pollinate when they “tassel”.  Tasseling is when you see the tall feather like shoots at the top of your corn plant and the tassels contains the pollen (this is the male part of the plant).  Lower on the plant is the female flower which we call silt’s.

Corn Cross Pollination 3

These are the bunches of fine silk like material that eventually will be at the top of your corn cobs.  The pollen from the tassels is blown by the wind to the silts, where the seeds are then pollinated and eventually become each of the individual pieces of corn on the cob.

This is why it is so necessary for you to plant corn close together in blocks or multiple rows.  So the pollen from one corn plant can spread to another.

This also explains why it is so easy for different varieties of corn to cross pollinate.

So let’s use sweet corn and popcorn as an example.  If you plant sweet corn and popcorn together, popcorn is the dominate gene. So if (and when) pollen from your popcorn is gets on the silt’s of your sweet corn, cross pollination will occur and the dominate gene’s in the popcorn will ruin your sweet corn, giving your “funky” stranger tasting corn.

So how do you prevent this corn cross pollination?

There are 3 methods.

1.  Only plant one variety of corn per year.

If you want sweet corn, then choose one variety of sweet corn that year so there is no risk of corn cross pollination.  And make sure if your neighbors garden (anyone within 100 feet of your garden) that they also plant the same or a similar variety of sweet corn.  Yes fences or large buildings between your garden and your neighbors will help, but they are no guarantee.

2.  Distance

Distance between varieties can prevent corn cross pollination.  100 feet is usually considered enough distance to prevent any significant cross pollination.  A house between (or some other large structure) may also help.  But if you want 100% pure seed (for example if you are planning on saving an heirloom seed for next year). Then really 1000 feet is the max safety zone!

3.  Time

The other method for preventing corn cross pollination is timing.  The way this works is you separate the time different varieties are pollinating by planting those varieties at very different times.  Say at least 3 or 4 weeks apart.  This means that one variety is done pollinating before the other starts setting tassels.

Separation by time can also be accomplished by planting varieties with vastly different tasseling times.  Try planting an early maturing sweet corn with a late maturing popcorn.  This one requires you don’t some homework and may also mean a little trial and error for a few years.

Corn Cross Pollination 4

I understand this corn cross pollination is a bit complicated, and it can also be a bit of a pain in the neck.  Do your research before you plant different varieties of sweet corn together to be sure they wont cross.  And remember that you can never plant popcorn or field corn (Including those fancy colored decorative corns) together with sweet corn.

Questions???  Ask away in the comment section!

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