Tuberous begonias have magnificent flowers. To keep them growing year after year, the tubers must be dug from the ground and stored during cold weather. Fleshy begonia tubers will rot if left to over-winter outdoors.
Dig up around the perimeter of the foliage (called the "drip line") with a shovel or spading fork after the foliage has turned brown in the fall.
Lift the clump of soil gently and lay it in a protected sunny location until the foliage dries completely. Make sure the tubers receive no water during the drying process.
Cut away the foliage and wash the excess soil off of the tubers, using a shower head nozzle (not a jet sprayer). Be careful not to damage the outer skin.
Lay the prepared tubers on sheets of newspaper in a single layer. Allow them to air dry in a sunny location for one week.
Dust the prepared tubers with sulfur powder to prevent fungus disease and rot. Sulfur powder is available at nursery supply stores.
Store tubers in a cool, dark, dry location. The tubers can be stored in single layers in a cardboard box or nursery flats lined with newspaper.
Plant again in spring after the soil has warmed.