Because of differences in the growing season for corn across Ohio, practitioners need a method of accurately rating crop’s maturity to inform crop management decisions for adequate yield, quality, and grain moisture at harvest. For this reason, we rate hybrid maturity based on “Growing Degree Days” (GDD), or heat units. Because a corn hybrid requires a specific number of GDD to reach maturity—a number that is independent of the crop’s total number of growing calendar days—the GDD method is accurate and should be considered by today’s practitioners.