Has it recently been watered a lot, like with heavy rain if it's outdoors? A 12" pot is pretty big, but I do grow some of my rhizomatous begonias in pots that size. It is, however, very important to let them dry quite a bit between waterings. Yours sounds like it could have root-rot from over-watering, and if so you should consider taking out the green section and re-potting it in something smaller, and with a well-draining mix. I may be guessing wrong, of course--be sure to check the roots to see if they look healthy.

I normally water it once a week and it is not outdoors. Thanks, I'll try cutting back on the water since it is in a self-watering pot. And will consider repotting the lush green section.

Do you know if they bloom? I have a picture of one blooming but neither one of mine has. My smaller potted one is still green and beautiful and it gets watered once a week and it is also in a self-watering pot.

They bloom in late winter/early spring, but maybe they need to be semi-dormant first. I wick a lot of my begonias, (same principle as 'self-watering') but make a point of letting the reservoir go dry for a few days before re-filling it. Of course, outside they're more dependant on rain, and sometimes get pretty dry before they get watered. Don't know if that affects the blooming or not, but I wouldn't be surprised. Actually, the flowers of most rhizomatous begonias are not really knock-outs, tho' the clouds of little blooms are rather attractive. And indoors they can make a bit of a mess! I think they really tend to need a cooler, drier rest in winter.

Thanks for the information. I'll just be a bit more patient.