Growing degree days are calculated by averaging the daily maximum and minimum temperatures and comparing it to a base temperature. This formula subtracts the base temperature from the average daily temperature and calculates the number of heat units for that day or GDDs. When the GDDs are less than zero, it indicates no growth or development occurred on that day. Only GDD’s above zero are accumulated. The base temperature options for this calculator include 32°F, 50°F, 0°C, and 10°C, which should be selected based on the desired growing degree day model or target organism.

Since weather patterns can vary from one geographic area to the next and from year to year, GDDs allow turf management professionals to monitor heat accumulation in their area, which translates to the development of plants and insects. By tracking GDD days, you are able to refine product application timing based on actual weather patterns in your area rather than a predetermined calendar-based schedule.

Sign-up for Growing Degree Day email alerts that are specifically targeted for your course.

When it comes to growing degree day models, it is important to remember that although they serve as useful guides, they don’t replace scouting techniques or your own observations on the course. It is also important to note that for the most accurate GDD data, it’s recommended you utilize an on-site weather station. That said, models such as this do serve as a guide to help you compare month over month and year over year.

If you do have your own weather station, you may see some variances. Reasons include:

• The location of your weather station and local station feeding this model may be exposed to differences in elevation, proximity to water, shade/sun, and wind.
• Online model accumulations are reported once a day at midnight each night. Your station will report in real time.