Growing degree days aren’t perfect, but they are a more reliable way of predicting when a crop will mature than looking at the calendar.
There are many ways to figure growing degrees, but unless you like to use an app or a computer spreadsheet, it’s probably best to stick to the basic formula.


 To figure growing degree days for warm season there  are two numbers that are very important to know: the base temperatures of 50 degrees and 86 degrees Fahrenheit air temperature.

For those of you that like to keep it really simple, corn or sorghum will not grow and mature unless the average temperature for the day is between 50 and 86 degrees. Humidity is not factored in to the heat equation.

So what about a day that averages 50 degrees, but starts out at 70? Or a day that starts at 65 degrees but reaches over 90? What about that? That is what the calculation is for-here is the simplest one:

Degree day accumulation = The average between the high and low temperature for the day – 50 degrees.  Any negative number is just recorded as a zero.

For example, let’s say a day got to 83 degrees and fell to 61 at night. The average between the high and low is 72. 
72-50 = 22 accumulated growing degrees for that day.

Then add the accumulated growing degrees on a daily basis to predict maturity starting when the plant emerges from the ground.

The number of growing degrees needed for corn to reach black layer is about 2700-depending on the variety and another 200-300 for dry down. A total of about 3000 growing degree days, for easy figuring.

This year, corn silage harvest is 11 days behind the average in our area, according to the USDA report released earlier this week. Our average growing degree days, depending on the plant emergence date and variety, sits at about 2400 GDDs right now.

Hope this helps.