Geraniums are one of my favorite flowers for the summer season. I like to plant three or four of them in large pots. I put the pots out in the full sun, water the and feed them a lot. Geraniums are annuals and are inexpensive at nurseries in the spring. A really cool thing about this flower is that you can keep them over the winter and have bigger more robust plants in the spring. The easiest way is just to bring the pots indoor, my pots are way too big. Here is another way:
Dig out the individual plants and shake off as much dirt as possible.
Trim off the tops of the plants 3" to 4" above the base of the stem.
You can see the 4" pieces of stem above the roots. The roots are thick and full of water, like a succulent plant. This stored water allows the plant to be stored.
Store the trimmed plants upside down in a bag or box, store in a cool dark place. Check the plants every month. Soak the roots in room temperature water for an hour or two each month if the stems are getting shriveled. The plants need to be stored at temps above freezing, 45 to 55 degrees is best.
The plans can also be stored with out trimming, hang the entire plant upside down in a cool dark place. A good place is from floor joist in a basement or crawl space. I don't use this method as I don't want dirty plants hanging in my basement.
You can replant them in March, in appropriate sized pots with potting soil. They will be ready in the spring when it's warm enough to set them out. Pinch off long, fast growing shoots to make the plant bushier with more blooms.