I downsized the pot my diffenbachia was in, it was in a HUGE pot cause it had toppled over into a U shape and it was so weak that I didn't want to cut it. So I put it in a big pot and let the bottom of the U in the soil. A few months later I lifted it up and there were new roots :D So I cut it but then it wasn't as happy. After browsing this forum I learned the pot was too big and the MG soil wasn't the best. I still had to use MG soil, but downsized the pot so it wouldn't take so long to drain. And really, the roots on even the original stem were pretty small.
So we'll see how it likes that. Also, should I chop the stem back more? How long does it take for a new one to start? I've done it before but it was so long ago that I don't remember how long it took. Thanks!