growing degree days, heat unit, temperature
The term “growing degree days” (GDD) has been around for sometime and most farmers refer to them as “heat units.” Scientists know that temperature is the one environmental factor needed for plant growth which can be measured in order to give them an estimation of plant maturity. There is no universal definition for heat unit and its definition can vary from one crop to another. Agronomically, the most commonly used heat unit if for corn. The heat units of various crops are basically similar to one another except for the temperature limits included within a given formula.
Hall, Robert, "What are Heat Unit or Growing Degree Days (GDDs)" (1995). SDSU Extension Extra Archives. 308.