How Do You Keep Rieger Begonias Blooming?

How Do You Keep Rieger Begonias Blooming? Temperature. Reiger begonias need average to warm (and humid) temps. They can go as low as degrees Fahrenheit at night in the fall to help stimulate a bloom. How do you maintain a begonia Rieger? Fertilize the Rieger begonia once a month with a high-phosphorous liquid plant food