Tuberous begonias have a winter dormant period that is determined by the day length, and in cold climates, by the weather. This dormancy is a normal part of the life cycle of the tuberous Begonia. The time to ready your tuberous begonias for storage depends on climate.
Northern and Cold climates:
In areas that freeze during the winter, tuberous begonias must be dug up and the tubers stored indoors for the winter. The time to do this is after you have had that first light frost that ruins the foliage. This is a type of dormancy forced by the weather. A light frost will not damage the tuber under the ground, but a hard one will.
Southern and Warm climates:
In areas that do not or rarely have frost, tuberous begonias go dormant on their own, according to the length of the day. They usually reach this point in October or November. When they start to collapse, turn yellow, drop leaves and stems, you need to stop watering.
What to Do
Northern and Cold climates:
In cold climates, after the foliage has been ruined by the first light frost, dig up the entire plant with its tuber. Gently remove all the soil from the tuber and any loose roots. Check for pests or for rotted areas. Rotted areas can be removed with a sharp knife and dusted with a fungal powder or sulphur. Lay the entire plant in a warm, dry area for several days to thoroughly dry the tuber. Make sure to bring them indoors at night if it is going to freeze. Once the tuber is dry, the stems should detach easily. If they do not, this means it is not dry enough yet, and you need to wait a while longer. (Do not be overly concerned if you break tops off while digging or by accident; they should still be fine. It is simply better if they come off naturally, because there will be less chance of rotting.)
Southern and Warm Climates:
In warm areas, your main worry is keeping the tubers dry during the winter. If you are growing them in the ground, it will be difficult to stop them from being watered by rain and you will need to follow the directions for northern climates to dig the tubers and store them. If you are growing them in pots, however, all you need to do is put the pots where they will not get wet, or else turn them on their sides so they cannot be watered.
How to Store
Northern and Cold Climates:
Once your tubers are thoroughly dry, place each tuber into a separate paper bag and place the bags into a cardboard box for storage. The reason for the individual bags is so that pests or disease cannot spread easily to the entire collection, and because they will allow the tubers to breathe. Keep the box in a dark, dry, cool place for the winter (cool, not cold – slightly below room temp). Check the tubers periodically to make sure none are rotting and that no pests have gotten into them. Again, rotted spots can be removed and the tuber redried and dusted with sulpher if they are not too bad.
Southern and Warm Climates:
As stated above, if they are in pots they can be stored right in the pots by either tipping the pots on their sides or storing them in a cool, dry, dark area where they will not get wet. Follow the cold area directions for tubers that are dug out of beds.
