CEDAR RAPIDS, Iowa (KCRG) - Growing degree days (GDDs) are used to help figure plant growth during the growing season. It’s calculated using the day’s average temperature compared to 50 degrees. For example, if the low was 60 and high was 80, the average temperature was 70, giving 20 GDDs. A high temperature above 86 is “reset” to 86, since little growth occurs warmer than that.
In the case of corn, roughly 2500 GDDs is generally the minimum target. Since planting happened so late, there has been less time to accumulate GDDs, which means a freeze is the looming threat. Since June 1, Linn County is at about 2000 GDDs. On average, the last week of October would make the 2500 GDD mark after a June 1 start. Warm weather and a late freeze would help us get there.