Growing Degree Days: A Guide for Beginners
Introduction
Growing Degree Days (GDD), also known as Growing Degree Units (GDU), are a way to measure the development of plants and insects during a growing season. By using data calculated from air temperatures, “heat units” can more accurately reflect growth stages than the calendar method. The concept is that growth and development increase with air temperature but stop at a maximum temperature.
Calculating Growing Degree Days
To calculate GDD, you need to know the base temperature, or “threshold,” below which a certain insect or plant will not grow or develop. Then, add together the high and low temperatures for the day and divide by 2 to get an average. Subtract the base temperature from the average temperature to get the GDD amount. If the result is a negative number, record it as 0.
Using Growing Degree Days
GDD is important because it helps researchers and growers predict when an insect will enter a certain stage of development and when a crop will reach a certain growth stage. This information can help with pest control and crop management.
How to Use Growing Degree Days in the Garden
Gardeners can use GDD to predict the growth habits of their plants. Software and technical monitors can be purchased to record temperatures and compute the data. Your local Cooperative Extension Service may distribute GDD accumulations via newsletters or other publications. You can also figure your calculations using weather data from the National Oceanic and Atmospheric Administration (NOAA), Underground Weather, etc.
Threshold Temperatures
Threshold temperatures vary for different insects and crops. Your local extension office may have the threshold temperatures for various insects and crops in your area.
Related Terms
- Air temperature: The temperature of the air around a plant or insect.
- Base temperature: The temperature below which a plant or insect will not grow or develop.
- Calendar method: A method of predicting plant and insect development based on the calendar date.
- Crop growth: The development of a crop from seed to maturity.
- Growing season: The period of the year when plants and insects can grow and develop outdoors.
- Heat units: A measure of the amount of heat that a plant or insect has been exposed to.
- Insect development: The process by which an insect grows and develops from an egg to an adult.
- Seasonal comparisons: A comparison of the growth and development of plants and insects over different seasons.
Tips for Using Growing Degree Days
- Use GDD data to predict when pests will be active and take steps to control them.
- Use GDD data to predict when crops will reach certain growth stages, such as flowering or maturity.
- Use GDD data to make seasonal comparisons and identify trends in plant and insect development.
Conclusion
Growing Degree Days are a valuable tool for researchers, growers, and gardeners. By understanding how to calculate and use GDD, you can gain a better understanding of the growth and development of plants and insects.