Growing Degree Days
Plants require energy to grow and develop, and some of this energy is in the form of heat. Many climatic factors influence the wellbeing of a plant but temperature is the single most important factor contributing to plant response.
What are Growing-Degree-Days?
The concept of Growing-Degree-Days or heat units has evolved as a means to relate plant growth, development and maturity to temperature. Growing-Degree-Days (GDD) are a measure of the accumulated amount of heat (in degrees Celsius) above a base temperature taken from one point on the landscape over time. The concept of GDDs assumes that plant growth is directly related to the average daily temperature. It disregards factors such as soil temperature, differences in the pattern of night and day temperatures and other variations caused by the stage of growth of the plant. The GDDs for each day are added together, or accumulated throughout the growing season.
Why use Growing-Degree-Days?
The accumulation of GDDs is considered a more precise way of predicting crop maturity than simply counting the passing days.
Temperature affects plant processes mainly by controlling the rate of growth. Plants do not grow below a minimum temperature. The actual minimum depends on the particular plant involved.
For general plant growth, a base or threshold temperature of 4°C is probably most valid; however, many crops have been assigned their own base temperature after experiments or field trials.
These Topoclimate Long Term Annual Heat Pattern maps show the distribution of heat in Growing Degree Days across the Southland landscape.
Growing Degree Day Application
To view this application, please click on the link below or the image to the right and it will then launch in a new browser window. You may have to temporarily allow popups for our website (depending on your browser) in order for this to open correctly.
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