How do I get my cane begonias (B. Lubbergei) to bloom?

I had posted in the plant identification when I didn't know what it was. Now, I have what it is. I have transplanted it in two parts to two new planters. I pinched all the long leaves and now it is full of new growth. This has been since May. I've also had them hanging outdoors all summer. At first they looked just awful from the transplant. Now they look incredible. I'm amazed because it's scorchingly hot here right now and they're still looking beautiful! They get full afternoon sun. I'd had one hanging on the other side and the morning sun with afternoon shade was killing it. So I moved it to the other side with the other one which looked fine.

I have been fertilizing once a week. Watering daily (it's HOT). No blooms yet. Any thoughts?