I bought my E. trigona 'Red' two and a half years ago, a little before leaving the garden center job. It survived fine and was willing to grow for me, but it didn't produce any branches, on any of the five stems in the pot, for the first two years I had it. This seemed especially strange because the green version of the same plant was branching a lot.
So this spring, I divided the five stems into individual four-inch (10 cm) pots. Four months later, three of the four that remain (one was traded away) are beginning to branch. This makes me happy, in that they're doing what they're supposed to do, and a little anxious, because this signals that they're going to become increasingly top-heavy in a hurry, and they were already pretty top-heavy. But overall I think I'm more pleased than anxious.
I don't know if the timing is just coincidence or not. It makes sense that crowding cuttings in a pot might inhibit them from spreading out, that maybe they have some sense of how close their neighbors are and behave accordingly. (I have vague memories of reading something to that effect once, even.) But it's also possible that this had nothing to do with the division, and is instead a much-delayed reaction to the fertilizer I started giving them six months earlier. Has anybody else had this experience before, where a Euphorbia started branching when it got different treatment?