“What is the coldest temperature petunias can handle?” Question from Barbara of Racine, Wisconsin
Answer: Petunias are true warm-season annuals that cannot withstand really chilly temperatures without damage. Ultimately, they grow best when nighttime temperatures are between 55 and 65 F. (14-16 C.) and daytime temperatures are between 61 and 80 F. (16 to 20 C.). Many newer cultivars are able to withstand hotter temperatures, but no petunias thrive in chilly temperatures. When spring temperatures dip below 40 degrees F, either cover your outdoor petunias with frost cloth or bring them indoors. Temperatures below freezing will kill them in a jiffy.
Black Gold Horticulturist