this will die back in the autumn and next year the new growth will start from the base.
I just take stems off and push them into damp compost and they do tend to root easily.

Or you could lay the stem, still attached, onto the surface of another flowerpot filled with compost and keep it attached until it roots. Either pegging it down with hairpins or similar or laying a stone across to keep it in contact with the damp compost.

I'm going to try both! Thanks both your your responses.