Rieger begonias are bushy, compact and profuse bloomers. I found a rosy pink Rieger at Publix a few weeks ago. One or two of the buds were in bloom, but there were dozens more to come, so I bought it.
It has been a spectacular plant so heavy with blooms, it can hardly hold its branches up. The leaves are large and glossy and the flowers are doubles. Since it's still winter in Florida, I've got it in my west window because they need a lot light in winter. However, I do close the verticals for a couple hours when the sun is hottest.
Don't overwater this plant and don't get the leaves wet. They don't like it and are susceptible to powderly mildew. Check the soil first to see if it's dry to the touch. I water it in the sink so it can drain for a few minutes before I put it back in its spot. The fertilizer recommended is a water soluble one with numbers 15-30-15.
When the plant begins to fade, stop watering for a week or so. Then cut it back to 3 or 4 leaf nodes. Let it stay dry for another week, then water slowly and thoroughly to completely soak the plant. Sprouts will grow around the base of the plant and then it will eventually bloom again. If you are successful and do get a second bloom cycle, try it again for a third time. Riegers don't like to be root-bound, you may need to repot it in the next size pot.