Answer: Tuberous begonias, including the Nonstop series, are treated similarly to other non-hardy tubers so your grandmother should have good luck storing them in her basement.
In the fall, when the leaves and stems yellow and fall off naturally, carefully dig the tubers. Some gardeners wash them and let them dry, some simply let them dry before storing. Then pack in sawdust, peat, sand or vermiculite and store under cool but frost-free conditions (approximately 40 to 60 degrees) for replanting in the spring.
Some gardeners presprout the tubers indoors in February or March to increase the growing season
outdoors. To do this, plant the tubers very shallow with the top (dented side) above the soil surface. Keep the temperature between 65 and 70 and water lightly. Then, when new growth is 3 to 4 inches tall, repot them and cover the tuber.
Good luck with your begonias!
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