Petunias are an annual flowering plant with long, trailing stems and colorful blossoms. Petunias are often a gardener's choice for hanging baskets, sunny borders, window boxes and flowerbeds. Petunia flowers make up two groups of plants. One is the Grandiflora variety and this variety has larger, yet fewer, blossoms and long stems. The other group is the Multiflora variety and this variety has compact growth and smaller, yet more, blossoms. Petunias are generally tolerant of cold temperatures and often even withstand a frost if they are acclimated to cold temperatures prior to the frost occurring.
Watch the weather for indications that a frost might be coming. If temperatures might dip below freezing overnight, prepare the petunias as early as possible in the days before you expect freezing temperatures.
Water the petunia plants around the base of the plants without getting the foliage wet. The water will help to insulate the soil and keep the cold weather from damaging plant cells. The temperature of damp soil will stay higher than dry soil.
Cover the petunia plants with the thick blanket, large bucket or large box. If you are using a blanket, drive a stake in the soil near the petunia plant to hold up the blanket away from the foliage of the plant.
Secure the blanket, bucket or box with large stones to hold it in place over night.
Remove the covering in the morning when the outside temperature is above freezing again.