Usually just before to right after the last frost of the year. You may have to guess as we have an unusual frost tonight. Very late in the year for us. So I just cover up what needs to be and hope for the best.
I think I will look for some seeds this weekend. We are having crazy weather here, so I have no clue when our last frost will be. I think I will start them indoors and move them outside when I am sure the weather will stay warm.