Someone asked me if they should get the Sunflower seeds in before a possible storm. Here's my experience.
I grew them one year. The Hot Oklahoma sun couldn't kill them. I forgot to water them. they didnt care. We had a few torrential rains that flooded them. Nope, didn't bother them. Then the birds came, do you think they gave a crap? No. The weeds tried to choke them out, LOL! LOL!
When winter was coming, I chopped them down. Some seeds fell in the dirt, some the birds got, and I got a few. Freeze, warm, freeze, warm, snow, freeze, warm, Rains and flooding. Guess what came up? Those dang sunflowers! But that's not the worse part. They came up in my backyard, Front yard, near the road and neighbors yard. I even had one sprouting in my driveway. He was doing great until my neighbor ran over the little guy.
So when should you plant Sunflowers? When you get them! Just chuck 'em. There coming whether you want them to or not.