Answer: We're all novices when we start out, and experimentation is how we learn! But I will say that it's time to let the begonias recover from their leaf losses. A more reliable way to increase your begoinas is through division of the tubers.
Since tuberous begonias are tender bulbs, you should "lift" them this fall and store them inside for the winter. Leave the plants in the ground until the leaves and stems wither and fall off. Dig the tubers, allow them to dry off in the shade, and brush the dirt from them. Then store them in dry peat moss in an onion bag for the winter. In the spring, new little buds will sprout, indicating that it's time to replant. Then you can divide the tuber by cutting it into pieces, each with at least two buds, and then replant.
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