Growing Degree Day
Growing degree days are a measure of how many heat units are accumulated in a single day or over time. They are calculated on a daily basis using the daily maximum (Tmax) and minimum (Tmin) temperature. This indexing system is useful in determining how the season is progressing, whether the crop is ahead or behind and which varieties are suitable to a particular location
The following equation is used to calculate daily GDD:
Daily GDD = ((Tmax + Tmin) ÷ 2) - Tbase
Tbase = the GDD base temperature for the organism being monitored
GDD values are generally accumulated from from Apr. 1 to Oct. 31.