Excellent info. Thanks! I have a tall skinny cactus in our window that I'm having to stake to keep it upright and it's now beginning to branch into two, making it even more top-heavy. I had no idea that trimming the top was an option. I have several window cacti and I really love them. We get so much rain here that there is no chance of keeping them outdoors so they seem a bit exotic.
Thanks for the reply.
Cactus can be like an exotic plant in some regions, in other places they're almost the only plants that will survive.