I have a sinningia that was given to me 3 years ago. The first winter it went dormant, and i waited for it to start growing. I waited and waited and . . . I always felt the tuber and it was always firm almost hard. Never mushy, or hollow feeling so I just kept caring for it. Just a couple weeks ago, I knocked it off the bench, and though I thought I should just toss it, I tossed into a pot with another plant and put its pot in the pot pile.
Today I was out watering and low and behold leaves had emerged from the tuber and it had rooted into the soil. I removed it with as much soil as ai could and repotted it. I am just amazed ! What I am wondering is it common for one to go dormant that long? Its lucky I'm a die hard and as long as the tuber felt right, I kept it. And I'd about given up myself.