What is a Growing Degree Day (GDD)? A growing degree day (GDD) is a method to track the heat units that have accumulated and are needed for plant growth and development. The formula for calculating GDD is:
GDD = ((max temperature °F + min temperature °F) ÷ 2) - base temperature °F, where the base temperature is normally either 22, 32 or 50 °F but varies based on the model.
For example, if the high today was 74°F and the low was 52°F and we used a base temperature of 50°F, our calculation would be, GDD= ((74°F + 52°F) ÷ 2) - 50°F = 13
Models that help us predict plant development use accumulated GDD which is simply adding the GDD calculated each day and determining how many GDD units have accumulated thus far.
GDD = ((max temperature °F + min temperature °F) ÷ 2) - base temperature °F, where the base temperature is normally either 22, 32 or 50 °F but varies based on the model.
For example, if the high today was 74°F and the low was 52°F and we used a base temperature of 50°F, our calculation would be, GDD= ((74°F + 52°F) ÷ 2) - 50°F = 13
Models that help us predict plant development use accumulated GDD which is simply adding the GDD calculated each day and determining how many GDD units have accumulated thus far.
In some cases accumulated GDD can be used to monitor when weeds might germinate or flower or when grasses might produce a seedhead while in other cases accumulated GDD can be used to help optimize application timing such as with preemergence crabgrass applications or the selection of amines or esters for spring broadleaf applications. Research into plant development and optimal herbicide application timing has determined a window of accumulated GDD needed to best predict when to time these applications or when these events might occur.
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