Answer: Tuberous begonias are actually tubers rather than bulbs, so they do not divide naturally the way a bulb such as the daffodil or tulip would do. Instead, you could propagate one by rooting stem cuttings (use about a three inch tip cutting, place it in a sterile potting mix or sand, it should root in about six weeks) or by dividing the tuber. To do that, use a sharp knife and cut the tuber into pieces so that each piece has at least one growth eye or bud and plant as one would normally to start them. Since the injury due to cutting may invite fungal infection, you might want to treat the cut pieces with a fungicide prior to planting. In my experience, the tip cuttings give very satisfactory results and allow the parent plant to grow and develop with minimal disturbance; with a little experimenting you will find out which way works best for you.
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