Hi C. I've rooted them, how long is the piece that broke off? If long enough you might get two cuttings. Take a piece that has at least two leaf joints. Cut just below a joint, dust with no.1 rooting powder and plant in a moist, well draining potting mix, enclose it in a clear plastic bag and put it where it has good light or under a florescent light. I've also had some success rooting them in water in this case I've placed the cutting in a glass in only 1/2 inch of water, this was kept on the windowsill above the kitchen sink where I could easily keep an eye on it. I found the less water I had in the glass the better success I had.
You could possibly get a tip cutting and another from the piece with the root/tuber attached. If the leaves are big they can be cut back some. You will have to keep them growing right through the winter and the following growing season. They won't be really making much of a tuber until next fall, and then the tuber it makes will probably be quite small. I would also pinch the flowers off as they form, let all the strength go into making a tuber. Hope this is of some help.

A......

Thanks A. I have some hope. I just hope that the original tuber does well next year. It cost me a small fortune.
Chloecleome

Hi C, I know what you mean, I have a few B&L Begonias, Yellow Sweetie, Scarlet Pimpernel and Orange Cascade and I have started cuttings of these guys myself. You are right, they can be pricey :o).

A......

In all my silliness I collected seeds from my tuberous begonia's, has anyone tried this? What might I expect, if I start them in January in a green house what may I have in the spring/summer?? Thank you.

If the seed is viable and you have the patience you can expect some small blooming begonias in a few months. The key is patience and following good advice on the web (or books).

Try this site:

growing from seed