Store bare root geraniums by digging the plants before the first frost, shaking all the excess dirt from the roots and placing them in open paper bags in a cool dry place. An alternative to paper bag storage is hanging the plants upside down. An unheated garage, where the temperatures remain about 50 degrees Fahrenheit, is the ideal place for storing these plants.
Keep the roots in good shape during the dormant period by soaking them in water about once per month. Once they are thoroughly wet, remove them from container, and allow them to dry. Place them back in the bags, or hang them again. During the storage period, healthy plants drop their leaves, but the roots remain firm. Discard plants that develop soft, spongy roots.
Toward the end of the dormant period, remove the plants from storage. Inspect the roots to ensure they are healthy, and remove any shriveled sections. Trim the tips of the branches, and soak the roots in a mixture of water and plant food for a few hours. Transplant the geraniums to fresh potting soil, and water the pots thoroughly. Place the pots in a sunny window or under a grow light until they become green again and the danger of frost passes.