Hello ... hope I can help! If you mean the 'million bells' variety of small flowered petunias then, in the past, I have tried to over-winter, after hard cut back, on cool but not cold windowsill. Book says stem cuttings should then be taken in early spring and placed somewhere with bottom heat - unfortunately time passed me by and I didn't take cuttings, so cannot confirm how they would have turned out. The original plant didn't produce anything worth keeping!

I believe cuttings are quite difficult to take from any sort of petunias, and overwintering is at best a hit and miss affair. I have given up trying and just replace the plants each spring from the local nursery - they do it so much better than I could.