Although geraniums are grown as annuals in all but the warmest North American locations, you don't really have to give them up at summer's end. With just a little work, you can bring them inside to winter over. They'll do fine as houseplants, or allow them to go dormant for winter storage. The best time to bring them in is right before you have to close all the windows and turn the heat on. This will give your geraniums a chance to adjust to being inside before that big drop in humidity occurs with the use of artificial heat.
Bareroot Winter Storage
Dig up your geranium before frost is predicted. Gently shake the plant to remove all the soil from its roots.
Hang the geranium plant upside down and store it in a very dry, cool spot where the temperature won't rise above 50 degrees F. The basement or garage are good choices. Don't allow the plant to freeze. Many people like to store their bareroot geraniums in individual brown paper bags for the winter.
Soak the plant's roots in water for a couple of hours once every several weeks. Let them dry completely before returning the geranium to its storage spot. This should supply enough water to keep the stems from drying out and shriveling up. If stems do show signs of shriveling, spritz the plant with a little water and let it dry completely before storing. Don't panic when leaves begin dropping from the plant, as this is to be expected.
Take the geranium plant out of storage in early spring. Cut off any shriveled or dead spots.
Soak the roots for a few hours in water with liquid fertilizer added per the packaging instructions.
Plant the geranium in a pot of all-purpose potting soil and water thoroughly. Set it in a cool, sunny spot. Water only when the surface of the medium dries out.
Replant the geranium in its garden spot after all danger of frost has passed.
Dig up the geranium plant before the first frost predicted for your location. Move it to a 6- to 8-inch pot of all-purpose potting mix and bring it inside.
Cut the geranium back by 1/3. Water it well to evenly moisten the surface of the soil. Place it in a cool, sunny spot. Geraniums winter best with lots of bright light, daytime temperatures around 60 degrees F and overnight temperatures of 50-55 degrees F.
Feed the plant an all-purpose liquid fertilizer one week later, and once monthly throughout the plant's indoor stay thereafter.
Water the potted geranium only when the soil feels dry to your touch.
Replant the geranium outside when all danger of frost has passed in the spring.