I just can't seem to keep them going for long.

I have a Boliviensis 'Bonfire' that I've had for years - in summer it lives on a table on the patio, getting mostly filtered sun (it gets an hour or so of direct sun in the early to mid morning) and mostly just rainfall - I only water when we are having a dry spell.

The Grandis that HC McDole identified for me a few months ago is in the shaded corner of my south porch, and also doing well as long as I keep the tray under the clay pot filled with water.

Further, I also have a few pots of wax and angel wing begonias that are several years old - in part sun and watered when dry.

I just can't seem to hit on the right care for these hanging pot, beautiful double begonias. The current pots have withered/ rotted stems at the soil line. I have them in the shaded corner of that south porch, so they never get any direct sun. They are in the hanging baskets that I bought them in, but they are not hanging - they are on a table.

Less water seems the obvious answer, except I don't water them unless the potting medium is dry. Do they need more sun, more or even less water?

Help! What is the secret? (it is a secret for me, in any case). BTW I have never had any luck trying to grow them from the bulbs either.