Bringing your geraniums indoors for the winter
If you would rather not have to buy new geraniums (Pelargonium sp.) every year, it’s easy to take stem cuttings in the fall or overwinter them indoors. The best time to start new cuttings is in September, before the first frost.
Remove the tips (10 cm) of the strongest stems on your most vigorous plants, cutting under a node. Strip the bottom leaves and allow the cuttings to dry slightly before standing them upright in a pot filled with moist sand or vermiculite, placing it in a bright spot. Some growers sprinkle the ends of the cuttings with powdered charcoal to avoid root rot or with powdered rooting hormone. Transplant the cuttings once the roots are well formed.
If you would rather bring your plants indoors for the winter, repot them in good potting soil, place them in a sunny window and keep them well watered. Remove any weak or crossing stems and cut back all the others to about 20-25 cm: the stronger they are, the less you need to cut them back. In March, you can take stem cuttings of the geraniums you have overwintered indoors.