Calculating Growing Degree Days
After corn is planted, how many days are required for the crop to emerge and then reach maturity? This is the question on a grower’s mind as we watch snow fall in April. Corn grows in response to daily heat accumulation or growing degree days (GDD). Estimating GDD is a practice of collecting the daily high and low temperature, but the maximum high is 86 degrees F and the minimum low is 50 degrees F. Here is an example for three days: 1. High is 90, low is 65, GDD formula is [(max. temp + min. temp)/2]-50 = GDD accumulated. [(86+ 65)/2]- 50 = 25.5 GDD 2. High is 72, low is 46. [(72 + 50)/2] = 11 GDD 3. High is 63, low 42. [(63 + 50)/2] = 6.5 GDD 4. The total accumulated GDD for this three day example is 25.5 + 11 + 6.5 = 43 GDD. 5. Remember, GDD are not negative or reduced, it is a measure of accumulated heat during the growing season.