Degree Days (GDD)
Definition - What does Degree Days (GDD) mean?
In the context of wine growing climates, Degree Days or Growing Degree Days (GDD) is a measure of the average temperature of a growing region to produce flavorful, sweet grapes during the growing season of April through October. The GDD of a particular region indicates whether the region can be suitable for growing grapes for wine production.
WineFrog explains Degree Days (GDD)
Famous horticulturalist, professor and chair for the Department of Viticulture and Enology at UC Davis for over 20 years Albert J. Winkler is credited with the invention of the concept of Degree Days as a method to match the best vines with the best growing regions.
GDD is a way to measure whether a location has the right climate that will be able to grow wine grapes for wine production. As the wine growing season is typically from April through October, regions must have the correct climate to produce ripe grapes at harvest. Climates that are too cold will have a growing season that is too short for the vines to produce, grow and ripen the grapes properly.
Typically, a region will need to sustain a minimum temperature of 50 degrees F per day throughout the growing season. When the temperature drops below 50 degrees for sustained periods, vines are susceptible to frost, and the vine will struggle to complete its yearly growth cycle.