Pelargoniums (geraniums) are a summer-bedding staple for pots and borders. Unfortunately in the Uk they are too tender to grow outdoors all year in most areas. Which? Gardening magazine trialled different methods to find out the best way to overwinter them:

Taking pelargonium cuttings

It's easy to take cuttings from pelargoniums in summer and then overwinter them in a light, frost-free place. We had an almost 100% success rate and the plants put on an impressive growth spurt when potted on in spring and planted outside once the danger of frost has passed in May or June.

Caption: Pelargonium cuttings don't take up much space indoors

Other methods we tried:

Overwintering pelargoniums outdoors

Like osteospermums, pelargoniums are South African natives and we wouldn't expect them to
survive outside in cold and wet conditions. So we weren't surprised when the plants left outside died before Christmas.

Drying pelargonium plants and storing indoors

We tried the unusual method of drying some of our pelargoniums. The method is best used with woody-stemmed pelargoniums, although we wanted to see if it would work with our bedding geraniums. The plants were lifted out the ground and any remaining soil was shaken off. The plants were then hung from the roof of a shed where it was dry and frost-free. One pelargonium
made it through the winter this way, so while it isn't a method we'd recommend, it was fun to try and might be worth experimenting with. 

Lifting pelargonium plants and overwintering in a greenhouse

Overwintering in the greenhouse was far more successful and our plants thrived. However, you need to care for them all winter and they are susceptible to pest and disease attack. Our plants in Glasgow were attacked by aphids in the spring. The plants were also large and so replanting them would only be sensible for one year unless you cut them back.

Caption: Plants overwintering indoors need to be checked regularly and any dead material removed