Try to place them on top of a pot of damp, warm peatmoss sphagnum (e.g. with bottom heat, etc). Place the tubers up-side-down (the hollow side down, rounded side up). Leave them at 75F for 2-3 weeks, and they should sprout. check every few days. once they sprout, turn them right side up (hollow side up) and plant them as normal.

8-10" pots for begonias are fine. I like them grouped together, but mixed in with impatiens for example is fine. Make sure they get some shade from afternoon sun. Also if you keep them in pots, make sure you remember to water them. Don't water until the top 1" of the soil is dry but then water thoroughly so the water drains from the bottom. They can not handle standing water. Fertilize them every 14 days with 1/2 tsp Peters 20-20-20 or Miracle Grow 15-30-15 per gallon of water, or use 1 tsp OSMOCOTE every 2-3 months.

Jan, sorry about the time interval, I've just been lazy about returning to the site. Right now, in my living room window I have two fibrous begonias saved from a window box...and its now been about 6 weeks they have lasted there......in bloom. I don't expect them to continue for very long in the bloom stage. Whether they can be "saved" as I do my geraniums and tuberous begonia has yet to be proved. Last year I did the same thing and when I went to retrieve my others in February, the fibrous did not come back as I had hoped. I have seen reference to the fibrous being saved as I have NOW...in a western exposure window....but I haven't seen anybody suggesting they will act the same as geranium. One plant that is supposed to act the same is "coleus". With the new colorful versions of coleus available this is the one plant I think many will try to winter over...either in flower or otherwise. If you have a cool place to store the plant....possibly in the pot, maybe you will have better luck. I always use the "what if" approach. It ties up space in my coldcellar sometimes I think could be better used for something else.....but what the hey....

I don't know how they stand the mid-thirties. I start letting mine dry out about Labor Day.Some growing instructions used to say 'lay the pot on its side', I could never figure that out, thought it might be some form of tropism. . .However I finally ran across some instructions which said 'lay the pot on its side so the fall rains can't get in and start regrowth', Oh that was so funny, I never would have figured that out because we don't have much fall rain. Well, we all have different environments which is why figuring out how to do things can be frustrating.