Stems dropping off overwintering begonia?
I am attempting to overwinter a 'Sparkle' type begonia I got on sale over the summer. It did fantastic outside, but doesn't seem to be going too well indoors now. I have it in a cool basement with some light from a nearby window as well as a little artificial light from a grow light I have set up on the next shelf. I water when the soil feels nearly dry.
All of a sudden the stems began getting fragile and dropping off the plant. Even stranger is the stems look all right and even have new growth on them. Is this natural? Is it perhaps doing into a state of dormancy, or dying? If it is dying, what is the reason and can I save it? Am I watering too much? Do these need to stay fairly dry over the winter? Darkness perhaps? Maybe this guy needs humidity? Any info and suggestions on how to save it are much appreciated! I'm just not sure what is going on with it. Another begonia (think it might be B. soli-mutata) I have in the same location and am treating the same way is doing great.
Ps. What is the best way to propagate a begonia like this? I want to take at least one cutting in case the main plant should die out. Would taking a cutting/dipping in rooting hormone/ potting up be the best method? Does tenting it for extra humidity while rooting help?
Thank you much!