Frost Impacts on Sunflowers

Frost anytime before the sunflower crop reaches physiological maturity (R9) can cause damage.
Once sunflowers reaches the R7 stage (ray petals have dropped, back of head starting to turn
yellow), sunflower can withstand temperatures as low as -4° C, but temperature, duration and
crop stage will influence the type and amount of damage.

A killing frost in sunflowers is considered to be -4 to -5° C for 6 or more hours, as this low
temperature for the extended period is required to penetrate the thick layer in the back of the
sunflower head and start the dry down process. The follow will attempt to describe what
happens when a frost occurs prior to the R-9 growth stage.

For more details, click here.