You plant corn in rows 30" apart.
More Info: A recent study conducted by Iowa State University revealed that spacing the rows closer together resulted in very little yield benefit to spacing the rows at 30" apart. Adversely, the study revealed that spacing the rows farther than 30" actually had a negative impact on yield.
Corn Requires Wind Pollination
Corn requires wind pollination to perform well. Because of this, it is important that corn is planted to nurture these conditions. Research has indicated that row spacing at 30" results in optimal yields. The seeds need to be planted in blocks for better cross pollination rather than a few long rows. For example, 100 corn plants will perform better when planted in 10 rows, 10 plants per row versus 2 long rows of 50 plants.
Corn Is a Cross Pollinator
Home gardeners do not generally have unlimited garden space in which to grow their vegetables. Because space is limited it is best that a home gardener choose only one variety of corn to grow in a single season due to the threat of cross pollination between varieties.
If you have more space than the average home gardener and wish to try more than one variety be sure to plant the different varieties at least 250 feet apart. You can also try staggering the planting dates to ensure that the spacing between maturity of each variety is at least two weeks.