Select the different corn varieties you want to grow. Corn is almost always grown from seed kernels that come in sealed packets. On the back of the seed packet is information for the number of days to maturity for that particular corn variety. Days to maturity is the time from planting seed to harvesting corn. Maturity time is important to avoid cross-pollination.
Plant the corn variety with the least number of days required for days to maturity. As an example, one corn variety has 67 days till maturity, while another variety matures in 74 days. Plant the 67-day variety initially. For optimal pollination, sow the corn seeds in short rows, 12 to 16 inches apart, to form a block or square instead of long rows.
Sow the second corn variety 14 days after planting the first corn variety. The 14 days plus the second variety's longer growing time will prevent the varieties from pollinating at the same time, causing cross-pollinating.
Continue to plant your corn seeds every 14 days until midsummer for an extended harvest. By continuing to space your corn planting 14 days apart, cross-pollination will not occur.