How To Look After Begonia Tubers. You can keep these in an ordinary cardboard box somewhere cool and dry throughout the winter free from damp. To properly plant begonia bulbs start the begonias indoors in small pots or flats about a month before the last frost.
Flowering slows down and the foliage will start to yellow. Gradually decrease the amount of water you give your begonias and stop fertilizing them by the end of August. The tubers should be covered with no more than an inch of soil whether you plant them in the ground or in pots.
432019 Keep plants well watered but allow the soil to dry out between waterings this is especially important for tuberous begonias which can rot in waterlogged soil.
972011 How to Overwinter Your Tuberous Begonias When the time comes to dig up your begonias simply follow these easy steps. If the plants are in pots simply stop watering and move the pots to an area where the soil will stay completely dry during the winter. Provide a balanced water-soluble fertilizer monthly during the growing season. Move the plants outdoors on a warm day to a shaded protected place.