A couple of years ago I lost my 8+ inch diameter Begonia 'Bonfire' bulbs from a wet summer. I am potting up my begonia tubers now and I am tempted to plant them on their side so that water cannot collect on the top of the tubers. Has anyone else done this?

Interesting.. but I wouldn't. Turning it on the side is more likely to create rot in the deeper section, and the bottom and sides that are above ground won't grow roots to nourish it...

If you're worried about the bowl shape at the top cupping water and creating a puddle, divide the tuber in half. Eventually you'll end up with round tubers again, but you can keep dividing if you feel the concavity it too big/deep.

Do you bury the top of your begonia? Or do you plant flush to the soil?

I have been planting the tubers even with the top of the soil but online information days to plant them an inch deep. I don't want to divide them because they are starting to send up new shoots and I am afraid they might rot if I divided them now.

I've seen both in equal measure... flush or 1" deep. My question is then why? We know we don't ever want soggy begonias and a tuber that builds its own puddle is definitely bad,

So the question becomes fluid dynamics. Which will dry faster?, a puddle exposed to the air, or a puddle covered with peat that Will slow direct evaporation, but will wick moisture away from that cavity... very interesting question