Growing degree days (GDD), also known as heat units, are calculated by taking the average of the high and low temperature in a day, minus the base temperature of 50°F. The number of growing degree days necessary varies depending on the crop and maturity.
As you can see in the graphs below, the Des Moines and Red Oak locations have accumulated more growing degree days so far this year than the northern locations. However, the cold weather during the last week in April caused the cumulative growing degree days all across the state to come to a halt, but around May 2 nd warmer weather returned and growing degree days began to accumulate once again.
The second tab shows a comparison of GDD for the years 2012 to 2017 at the various locations. As you can see, the 2017 Iowa average GDD are currently ahead of 2013 and 2014, but are behind the pace of 2012, 2015, and 2016. In most locations, 2017 GDDs are in the “middle of the pack” when compared to data from 2012-2016.