I have two very tall, weak Cereus peruvianus. They've been with me since 2004, and for some of that time, I have just plain not had a good bright spot to keep them. Because of the lack of light, they get tall and weak, and because they're tall and weak, the number of possible locations is reduced, so it's this whole unhealthy-cactus vicious cycle.
Currently, the only location available to them (without cutting them down, anyway) is in a corner of the plant room, where the ceiling is 10 feet (3 m) high, as opposed to the 8 feet (2.4 m) or less everywhere else in the house. (More on that decision here.) The cacti have been okay there -- they're not growing much, and they're covered in cobwebs, but nevertheless they stay alive and grow and stuff. So occasionally it happens that, because they're right inside the door, we accidentally knock them over when we're bringing big things in or out, and because they are weak from being a little light-starved, when they get knocked over, it usually doesn't end well for them. Or for us, either, because there are not a lot of things that will ruin your day like a cactus falling on you.
So the last time this happened, it was with the taller of the two plants. When it hit, it landed on the edge of a shelf, so it basically snapped itself off at the point of impact. I straightened it back up, threw out the piece (I was tempted to propagate it, but I already had one cutting, from when the same thing happened with the shorter of the two plants, and I didn't see much point to doing another. I think this was also during a period when I was feeling unusually purgey w/r/t the plants, because of scale, or because I was tired of moving them in and out all summer, or something like that.), and waited for it to resprout. Which it did, in two places, up at the very tippy-top of the plant. And now one of those branches has reached the ceiling, meaning that I need to make a decision again about whether or not to start a new plant from it BUT WAIT THAT'S NOT WHAT THE POST IS ABOUT:
The post is about this:
One of the new branches is also producing roots, about nine feet in the air.
I knew that lots of plants (Monstera, Crassula, Chamaedorea) can produce aerial roots, including quite a few cacti (Selenicereus, Hylocereus, Schlumbergera), but it had never occurred to me that this was something that Cereus might do. How often would it really get the opportunity in the first place? It's not like they grow next to trees that they might attach themselves to, or anything.
So I figure I pretty much have to try to propagate now whether I want to or not. I mean, this is meeting me way more than halfway.