Vineyard site temperature - growing degree days (GGD's)

Growing degree days (GDD's) is a measure of heat accumulation over the growing season. Grape varieties differ in their heat requirements, it is therefore necessary to the an appropriate site for the variety being grown.

The growing season lasts seven months (1 Oct - 30 April) and in Central Otago GDD's over this period range from 800 - 1200 depending on the site location and season. A high monthly GDD for December (180 +) harbingers and good crop, while a high monthly GDD for March (140 +) speaks of quality.

Monthly GDD's are calculated by summing daily GDD's. This can be approximated by taking the average of the highest and lowest temperatures over a 24 hour period and subtracting 10 C. For example, the temperature at 4.00 am in the morning was 7 C and the temperature at 3.00 pm in the afternoon reached 27 C, the GGD contribution for the month is 7 ((27 + 7)/2 - 10). In some cases, temperatures under 10 C and over 30 C are replaced by 10 and 30 C as growth is deemed not to occur. For further reading Oregon Viticulture - Growing degree days (GDD's)

Celsius to Fahrenheit convertor

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