Corn requires warm soil temperatures in order to germinate. A standard guideline is to plant seeds when the morning soil temperature at a two-inch soil depth is 55 degrees Fahrenheit, or 50 degrees Fahrenheit at a six-inch depth.
According to Purdue University's Department of Agronomy, the prime planting window for corn in Indiana falls between April 20 and May 10. It opens about a week later for northern Indiana counties, and about a week earlier for southern Indiana counties.
To ensure a continuous supply of corn throughout the summer, plant an early variety that matures in 60 to 80 days, a mid-season variety that matures in 70 to 90 days and a late-season variety that matures in 90+ days in the first planting. Make a second planting and successive plantings of late-season varieties when three to four leaves appear on the seedlings of previous plantings.