Q. I want to grow some of the different colored corn. The seed package says to isolate. How far from the other corn does this have to be to avoid cross pollination?
A. When isolating corn there are four things you can do, separately or in combination, to minimize cross-pollination. Farmers often first consider distance, then time. Other considerations include barrier rows and wind direction.
For the home gardener it’s more important to isolate by TIME than by physical distance, barriers, or avoiding wind.
TIME ISOLATION – It’s very difficult for the home gardener to find sufficient space to avoid cross-pollination of corn. But it’s fairly easy to determine the days to maturity and then plant two to three weeks before or after, so the pollen from another variety is not in the air during the time your isolated variety is receptive.
Once pollen is released from the anther, which is in the tassel, it is viable for about 24 hours, so avoiding that time period is critical. And the plants from one planting can continue producing pollen for up to two weeks, so a minimum of 14 days should separate the tasseling time of the different types.
DISTANCE – According to a study by the University of California plants that are 12 feet apart will likely have 50% cross-pollination, and while pollen concentration is only 1% at a distance of 200 feet one study showed that cross-pollination of 1% required separation of 660 feet.
Other studies indicated 1% pollination occurred at distances of only 40 to 50 feet, but even that distance is difficult to maintain in the typical family garden.
BARRIER ROWS – A large percentage of contaminating pollen can be diluted by planting several rows of a different vegetable between different varieties of corn. For this to be really effective the barrier rows must be tall, such as pole beans, vertically-grown tomatoes, etc.
WIND DIRECTION – By not planting different varieties of corn down-wind from each other isolation can be improved, but not fully achieved.
If you can’t wait the requisite two weeks between plantings, the other three factors can be used to limit cross-pollination as much as possible.