GDD Calculation
GDD are calculated by taking the average of the daily maximum and minimum temperatures compared to a base temperature, Tbase, (usually 10 °C). As an equation:
GDDs are typically measured from the winter low. Any temperature below Tbase is set to Tbase before calculating the average. Likewise, the maximum temperature is usually capped at 30 °C because most plants and insects do not grow any faster above that temperature. However, some warm temperate and tropical plants do have significant requirements for days above 30 °C to mature fruit or seeds.
For example, a day with a high of 23 °C and a low of 12 °C (and a base of 10 °C) would contribute 7.5 GDDs.
A day with a high of 13 °C and a low of 10 °C (and a base of 10 °C) would contribute 1.5 GDDs.
Read more about this topic: Growing-degree Day
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