Petunias are relatively low-maintenance plants, but they can survive only within a specific temperature range. If you live in a region with extreme heat or cold, it's important to understand this range and how to protect your plants from inclement weather.
Most petunias freeze to death at about 30 degrees Fahrenheit. Petunias grow in regions where up to 210 days out of the year are above 86 degrees Fahrenheit, according to the American Horticultural Society. That is the society's highest possible designation for heat tolerance.
To prevent cold-related petunia death, dig up your petunias and replant them in indoor pots. Some garden stores also sell heated domes that you may place over your flowers during inclement weather.
While petunias are able to withstand intense heat, hot weather leads to increased water evaporation. During hot summers, give your petunias extra water. The soil should be moist to the touch, but not overly wet or muddy.