Begonia rooted in water
Early this year my tuberous begonia split. I grew one piece in water over the summer. How do I go about planting that piece now and can I winter it if it doesn't really have a tuber, as it only has roots?
Just go ahead and plant your cutting in a potting mix with good drainage - a cactus mix with perlite added 1/2 & 1/2 would be fine. Put the pot where it will receive several hours a day of sun; you can use electric light to supplement if you need to. Keep the humidity up as high as possible with pebble trays, and lots of other plants. This article has more information: https://www.gardeningknowhow.com/ornamental/flowers/begonia/begonias.htm