Am I able to separate a very large geranium into several smaller plants so it can be wintered successfully? It's always been taken into the garage for winter but it's simply too large to fit in the space I have for it now. I don't want to kill it!

I would then take a two pronged approach and at the point you need to take it in, prune it back to a manageable size, and then make some cuttings from the trimmings and root those on a windowsill.
I would think if the base had five or six stems of 6-8 inch length they should have plenty of resources to make it through the winter. If not, you have some cuttings as backup.

Agree. Root some stem cuttings, definitely.

Yes, take some cuttings. Geraniums are one of the easiest to keep going from cuttings. I know someone who has kept her original geraniums going for at least a decade that way.

Root those cuttings in soil? Rooting hormone?
I've been failing with stem cuttings of a scented geranium- thought I did it once.

Soil. Root hormone probably wouldn't hurt. I did read that the cut end should be left to dry for a few hours to form a protective callus and prevent rot.

sallyg said: Root those cuttings in soil? Rooting hormone?
I've been failing with stem cuttings of a scented geranium- thought I did it once.

I root them in potting mix and use rooting hormone. You don't NEED to use hormone but it DOES speed up the rooting process.