There are several different ways to save your little darlings over the winter so you can have BIG darlings next spring:
1. Take Cuttings
Ok, I know what you are saying, "Taking cuttings is not saving my geranium over the winter - it's making all new plants!" Well, yes. It is. But hey - beggars can't be choosers. It is easy, and you still have geraniums next spring - in fact you will have more geraniums next spring if you do it right.
Take a sharp pair of pruners or a sharp knife (be careful not to cut yourself - safety first!) and cut a 3-4" piece off the top of the geraniums - the bendy soft wood, not the hard older parts. Take all the leaves off of the lower part of the cutting, leaving one or two leaves on the top - no flowers. I usually cut the leaves in half too - remember, the little plant has no roots to feed the leaves. You can use a rooting hormone at this point, but with geraniums I usually don't. Stick the cutting (leaves up) halfway into a small container filled with vermiculite or perlite (both available at the local garden center) making sure the pot drains well. Put a small amount of water in the pot and place it - pot, plant and all - in a big zip-loc bag, or other type of clear plastic bag. Sit it in an out-of-the-way place, out of direct sunlight. In 6-8 weeks it will root. Take it carefully out of the container and re-pot it in potting soil. Keep it in a cool, sunny spot until spring and pot it back outside. Woo Hoo free geraniums!
2. Force the Geraniums Into Dormancy
Geraniums can be stored similar to the way you would store bulbs. They stock up all of the life they need in their stems to help them come back to life next year.
This is even easier than taking cuttings.
Carefully dig up your geraniums. Gently remove the soil from around the roots - you don't want any clods hanging on. Hang the plants upside down in a cool place, like a garage or basement. Ideally around 50 degrees. The leaves will wither and dry. Remove them if they don't fall off by themselves - you don't want any fungal diseases, etc. to climb back up into the stem. Every month take them down and soak the roots in luke-cold water for about an hour. In the spring replant the geranium in your pot on the front porch or directly into your beautiful garden and voila - free geraniums!
3. Keep Them in Their Pots
If they were growing in the garden dig them up carefully and replant them in a pot. Use a pot that is big enough to fit their root ball. Nobody likes shoes that pinch their feet! Cut off the top 1/3 of the geranium along with all of the flowers. Water the pot thoroughly and place it in a sunny location in your house. Most of us don't have locations that are sunny enough, so you might have to add some additional light. Florescent bulbs or bulbs made just for plants are available at the hardware store or the local garden center.
Note from me: If I have to buy light bulbs and fixtures and pay for electricity all winter to light the little darlings, I think I can afford a new geranium next year. Call me crazy. This is not my favorite method of saving a geranium - remember? I'm cheap. (and poor) But, if you like it and it works for you - good on ya!
So, there are three ways for you to save your geraniums from a cold and frightful death while giving you the satisfaction of knowing that you saved a little plant along with a few bucks.
Get your hands dirty!
P.S. They are actually Pelargoniums - but that's a story for another day.