Teddy, I suspect what you refer to are actually Pelargoniums, not Geraniums, (it's a common error, even google can't get it completely right!) Geraniums or "cranes bill" are hardy
http://en.wikipedia.org/wiki/Geranium
Pelargoniums are only tolerant of minor frosts,
http://en.wikipedia.org/wiki/Pelargonium
They are of the same plant family, the true geraniums do grow wild in parts of England.
In this area Pelargoniums will survive 2 out of 3 winters when planted close to the house, we are lucky being close to the sea where there is still some effect from the gulf stream, further inland by a mile or so and further east they are unlikely to survive outdoors. I've never heard of storing the plants as you describe, (for Dahlia tubers yes it works) the best plan is to take a couple of cuttings from each variety in the early autumn and keep in a frost free grenhouse or indoors (kitchen windowsill/laundry room?) after they start to grow iin spring take more cuttings and plant out when no more frosts are expected.