Growing Degree Days indicate where we are in the growing season by adding heat units. Heat units are calculated by summing the high and low in a day, dividing by 2 to get an average, then subtracting 50F. The base 50F is standard in temperate climates noting that most plants do minor growth below 50F. To be counted 51F is the minimum high allowed in the count, and lows below 50F are discarded, substituting 50F for that low in the calculation. Add these heat units through the growing season, and one gets the Growing Degree Day heat units below for that location to know how well a known variety will ripen fruit and wood.