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.



Crop Development

As a producer it is important to follow the maturity of your crop as it reaches certain growth milestones. Activities such as application timing, scouting, logistics management, labor management, imagery acquisition, pest/disease management, and harvest timing depend, in large part, on the growth stage of the crop. As with all activities in agriculture, timing is everything. Let me say that again. Timing is everything. And many times once you are late, the value in accomplishing the task at hand decreases dramatically or has no value or just can't be done.

Hybrid Validation

Seed companies publish the maturity times of their hybrids but a few base the start date on emergence vs. planting date so it is good to keep track of this data yourself. In some cases their is no published data available so the best way to obtain this data is through your own data gathering.

Insect Pest Management


As with plants and other organisms, insects are dependent on temperature for their development so basing activities on calendar days is not always sufficient. GDD's should be used as a guide to your pest control actions.

Every farmer I know is interested in GDD data. The question is not the data itself but the most efficient way to obtain reliable, consistent, delivery of the data. As with many other businesses, time spent acquiring data comes at a cost. That cost could be the time spent at the PC researching the best place to get the data instead of actual farming activities or it could be the upfront capital cost of acquiring a weather station. Not to mention the installation and, more importantly, the maintenance cost of the hardware.

We at ZedX have spent many years accumulating gridded weather data sets from both public and private weather networks and put this data through a vigorous QA/QC process. We can also calculate GDD's using any methodology, from the basic on through to the most complicated.

This GDD data is delivered into your Inbox daily throughout the growing season.

The sign up process is quick and simple, taking just a few minutes.

What else do you use GDD's for? Let us know and join in the conversation.

Please contact Nate Taylor via phone at (814) 441-1867 or email at taylor@zedxinc.com for more details.

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