We have to know what type of begonia. There are those that are tuber type, and those that are fiberous rooted. The tuber type, you let the plant dry out, and keep the tuber dry in a dry unlight place. I keep mine in the greenhouse on the floor. In spring, when it is ready, new shoots come up, and I know it is time to repot and water it. The fiberous rooted ones, have to be kept watered all winter, not a lot, just some to keep from dying. I have about 8 of those, and cut them back to about 3 in. from the soil, and water lightly in the winter. They are also in the greenhouse, which is kept at 50*.
Darlene

Tuber type or fiberous: how do you know which is which?
I have dug mine up and got them nice and dry. They are mostly generic but one is labelled " Eureka Bronze leaf Scarlet" I does have a mass of matted roots. I read that you should sprinkle them with sulfur powder to prevent powdery mildew but am having difficulty finding it except at a pharmacy for cosmetic use. Wonder if this is the same stuff? My local garden center had only a sulfur spray

Any advice appreciated