GDD are a measure of heat accumulation used by horticulturists, gardeners, and farmers to predict plant and animal development rates such as the date that a flower will bloom, an insect will emerge from dormancy, or a crop will reach maturity.
[1] In the absence of extreme conditions such as unseasonal drought or disease, plants grow in a cumulative stepwise manner which is strongly influenced by the ambient temperature.
Growing degree days take aspects of local weather into account and allow gardeners to predict (or, in greenhouses, even to control) the plants' pace toward maturity.
Unless stressed by other environmental factors like moisture, the development rate from emergence to maturity for many plants depends upon the daily air temperature.
GDD are calculated by taking the integral of warmth above a base temperature,[2] Tbase (plant type dependant, see baseline section): A simpler, approximately equivalent formulation uses the average of the daily maximum and minimum temperatures compared to a Tbase to calculate degree-days for a given day.
However, some warm temperate and tropical plants do have significant requirements for days above 30 °C to mature fruit or seeds.