The best ways to store geraniums during winter is to either keep them in containers and move inside or to dig them up and keep them in a cool, dark area. Geraniums are hardy plants that can tolerate overwintering inside.
To keep a geranium inside in a container during winter, the plant should be cut back to half its size, dug up and potted in a container. The geranium needs to be placed in a cool location with plenty of sunlight. Water the plant when the soil feels dry. The geranium can be transplanted outdoors after the last frost.
For dormant storage, the entire plant needs to be dug up and the dirt shaken from the roots. The plant then needs to be stored in a paper bag left open in a cool dark place where the temperature is around 45 degrees Fahrenheit. Once a month, the roots should be soaked in water for at least an hour, then the plant should be returned to the bag. The geranium can be transplanted outdoors in spring after the last frost.