To overwinter geraniums in pots, remove the plant from the ground, and plant it in a pot that is large enough for the rootball of the plant. Prune away about two thirds of the plant's stems, and water the plant generously. During winter, store the geranium in a cool room where it is going to have access to a lot of sunlight. Use a lamp if there is not enough natural light.
Another way to overwinter geraniums is by making them go dormant. To do this, remove the plant from the ground in fall, and get rid of any lumps of dirt there may be in the roots. Hang the plant upside down in a room where the temperature is going to be about 50 degrees Fahrenheit throughout winter. Take the geranium down once every month, and place its roots into a pot filled with water for about one hour. Place the plant back after this treatment. Don't worry if all the leaves fall off the plant, as this is supposed to happen. Plant the flower back in the ground in spring.
Taking cuttings from a geranium cannot keep the current plant alive during winter, but it does provide you with several new free plants. To take a cutting, cut about 3 to 4 inches off the green parts of the stems, remove leaves from the bottom half of the cutting, and insert the cutting into a well-drained pot that has vermiculite in it. Store the pot in a plastic bag for 6 to 8 weeks until the cutting develops roots, then transfer it to a regular pot.