You can find your reliable Frost-Free Date by using a chart from the National Oceanic and Atmospheric Administration (NOAA). Go HERE and select your State from the pull down menu. This will generate a PDF file with a list of NOAA data collection sites in your State. In the left column, choose the location nearest or most similar to where you live. Then read across. Use the middle threshold number (32°F) and right next to it, in the Spring column, will be the 50% probability date. This is your all-important average Frost-Free Date.
PLEASE NOTE: In the event of a partial government shutdown, portions of the NOAA website are suspended. In that case, find your frost-free date at the Old Farmer's Almanac website, HERE.