Head out to your flower bed or container garden before the first frost. Dig completely around the plant about 6 inches from the main stem to a depth of about 6 inches. Lift up the geranium plant using a trowel and shake off excess soil. Have a garden hose handy to gently rinse the root mass. This thorough cleaning removes soil borne pests that may inhibit the health of the plant when transplanted indoors.
Choose a high-quality potting soil to fill a clean plant pot. Use sharp garden shears to trim the geranium back to a 6 to 8 inch height. Clip the stems to a 45-degree angle to promote quick healing. Don't worry about removing a lot of foliage. This haircut will allow the plant to regenerate roots and produce a wealth of thick new foliage.
Set the geranium into the pot and fill in around the roots with fresh potting soil. Moisten the soil thoroughly and place the pot in a cool but bright location. Avoid placing the plant in direct sunshine. Water the geranium as soon as the soil feels dry to the touch.
For years, gardeners took their clean geranium plants into the basement for drying over the winter. These plants would make a miraculous recovery when warmed up after the coolness of winter. If you don't have space for potted plants, try drying the geraniums. Rinse all soil from the roots and lay the plants in a cool, dry space for 3 to 4 days to allow complete drying of the roots.
Place each plant inside a paper bag and fold down the top to seal the bag. Tuck these plants away in a dark area with a temperature 40 to 50 degree F. Grab a bucket once a month, fill it with water and let the plant soak for 30 minutes. Bag the plant and revisit it again in a month. When spring arrives, trim back dead foliage and repot the plant in fresh soil.
[Image Credit: Chamomile, Morguefile]