Growing Degree Days and their use in Agriculture

As the growing season continues to move forward it is now time to start looking at some of the data that will be important when planning in-season activities. One of the data sets that all growers watch is Growing Degree Days (GDD), aka Heat Units.

GDD's the total amount of heat required, between the lower and upper thresholds, for an organism to develop from one point to another in its life cycle. Tracking this data assists in application timing and, more importantly maturity of the crop to determine harvest timing.

In a laboratory, calculating this value with a constant temperature is very straightforward; however, calculating this in nature with the myriad of temperature fluctuations is a bit more involved. This has led scientists to develop more than one method in obtaining the value of heat units. These are, from the simplest to most complex mathematically; single triangle, double triangle, single sine, double sine, and Huber's. There is a good post regarding these methods and calculations at the University of California IPM Site.

There are many uses outside of Agriculture for Heat Units, but we are going to focus on their use in farming.