Why am I showing you a pot of dirt? Because it isn’t, really, of course. It’s an exercise in patience. Or, in other words, compost no plant before its time.
This is a rhizamatous begonia–no really. I have found that for me, some grow just fine 12 months of the year. And obviously, as you can see by this post, some don’t.
For years, what I did with the ones that didn’t was to put the rhizomes in with some other plant–maybe a large banana or or something that I was over-wintering. I would have the large tropical plant to look at for the winter, and in the spring, when I took the large plant outdoors, it would have something interesting at its feet. My banana now has several begonias in with it.
But I have decided to just let these plants be, in an out of the way spot. I will keep them just moist enough so that they don’t turn to dust. And I suspect, come spring, I will have a begonia again.
And if I am wrong, well, then I can always compost it in the spring.
Gardendaze 
I had the same thing happen to me with one of my begonias and I put it down the basement in the dark
I’m glad you reminded me about watering it occasionally I enjoy getting your emails and appreciate all the great tips
have a happy healthy prosperous 2019
In the basement–which probably doesn’t have much light–you will only need to keep it lightly moist. Mine is up in my living area, just back from my window a bit.
Some folks take them out of their pots and just nestle them lightly into that lightweight peaty potting mix when they put them in the basement. That way, they can see the instant that new growth begins. I have tried that myself and it worked pretty well.
Thanks for the good wishes for 2019. All the best to you as well.
Karla
No one has the patience for these anymore. They might buy them in bloom, but then discard them when they finish. They used to be one of the main crops of the formerly famous begonia growers around Capitola.
That is a symptom of our society, isn’t it? Nobody has patience, period.
Karla