The total time required for development of a sunflower plant and the time between the various stages of development depends on the genetic background of the plant and the growing environment. The average development of a large number of plants should be considered when determining the growth stage of a sunflower field. Later in the season, for stages R-7 through R-9, use healthy, disease-free heads to determine plant development since some diseases can cause head discoloration. A number or recently released and grown hybrids contain the stay-green characteristic. If this characteristic is present, yellowing or browning of the bracts may not be an accurate indicator of plant maturity. Maturity is typically reached within 2200-2300 growing degree days (Celsius) after planting or 120-150 days.