Those beautiful geraniums in your garden can be brought indoors for dormant storage, or replanted in containers to bloom indoors through the fall and winter.
Here are two comprehensive articles detailing exactly how to do that; the first, on this page, from Penn State Extension and on page two from the Iowa University Dept. of Horticulture.
Saving Your Geraniums Over the Winter
from Penn State Extension
Many gardeners like to keep their geraniums from one year to the next. This provides plants for the home in the winter and reduces the cost of new plants the following spring.
Rather than take cuttings, some people prefer to pot their best plants and bring them inside to overwinter. If this is your choice, cut the plant back to about one-third its original height. Carefully dig up the plant, and pot it into a five or six-inch flower pot. After you pot it, water thoroughly. Location and care is then the same as for rooted cuttings. A sunny, cool location is best.
Cuttings or “Slips”
There are several methods of handling the plants over winter. One way is to take cuttings and root them in the fall, just prior to a killing frost. Geranium stem cuttings, often called “slips,” should be four to six inches long. Take the slips from the tips of the healthiest stems. Remove the leaves on the bottom two inches of the cuttings. Stick the cuttings in coarse sand, perlite, vermiculite or a well-drained potting soil. Cuttings will root faster if you dip the ends in rooting hormone powder.
Stick the cuttings two inches deep in the medium and water thoroughly. Place in a north or east window or underneath artificial lights until rooted. This generally takes three to four weeks. After the cuttings have rooted, plant them in individual pots and put them in a well-lighted spot. Keep the soil evenly moist, and begin fertilizing monthly once new growth appears.
One of the old but very successful methods of carrying geraniums over winter is to dig up the entire plant prior to frost. Shake the soil from the roots and hang it from basement rafters. Years ago fruit cellars were quite common, and they made excellent places to hold the plants with this method. It will not work in many basements today because temperatures are too high and humidity too low.
However, some people report success with hanging geraniums in modern basements. Temperature and humidity seems to differ in every basement. Since there is no way of knowing whether this will work in your basement, try it with several plants.
If you decide to try this method, take the plants down occasionally, and place the roots in water for several hours. Then, hang them back up. Do this several times during the winter to prevent them from completely drying.
Whether you carry your geraniums through the winter as young plants started from cuttings, as old plants in flower pots, or dried plants hanging in the basement, keep them inside until all danger of frost has passed in the spring.
Find more information on Overwintering Geraniums from Iowa University.