What does GDD mean? Each crop requires exposure to a certain amount of Growing Degree Days (GDDs) or heat units to complete its life-cycle. For some crops, like corn and soybean, one can actually use GDDs to determine where a crop is in its development cycle. This information can be useful for determining when scouting should be done, and it can also allow one to determine when a crop is in an important growth stage.

Temperature data from: Agronomy and Environmental Sciences (AES)