The University of Kentucky Cooperative Extension Service recommends planting sunflower seeds between April 1 and May 10. These suggested planting times result in a September harvest, as the flower takes 120 to 130 days to reach maturity.
Planting times will vary a small bit among the different planting zones of Kentucky. However, according to the Ohio State University Extension, the best planting times occur after the soil reaches a minimum of 50 degrees Fahrenheit.
If you wish to double your crop of sunflowers in order to produce more seeds, you will need to plant another crop at a later time. This second planting should occur no later than June 20.