For Sunflowers, the timing of growth stage progressions through the season is dependent on both the variety and environmental cues such as day length, or temperature. The Sunflower growing degree day model developed by Montana State University, uses heat units and time as a method to estimate plant phenological stages through the growing season. This can be helpful as a crop management tool, or to predict harvest timing.
Calculating Growing Degree Days
For this model, a lower temperature threshold of 32F / 0C used to calculate growing degree day accumulation beginning at the time of planting. Growing degree days can be calculated from daily high and low temperatures, or via the Pest Prophet app, which uses hourly temperature data for a given field. This can be used to predict flowering, seed development, and seed hardening based on growing degree day accumulation. Sunflower heads will be dry for threshing at approximately 3282 GDD F after planting.
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