Gee, I don't understand that either, Mare2. Sometimes blooming takes a long time, but not growth. I just grow mine in a hanging basket in ordinary potting soil and it sends out 4 foot branches (or whatever you call them)all over the place. I never heard that they needed to be rootbound. They like more water than ordinary cacti, you probably already know that. How about checking with the cactus forum? Maybe they have an idea.

I would put it in a bigger pot. They don't get tall unless you train them that way. They will branch out however. Pot bound is not as important as reaching a mature blooming size.

You've both been a big help. The leaves came with no instructions--just "stick them in soil"--so it's been one big experiment. In fact, it was actually marked Hylocereus Undulatus, but I'm pretty sure it's not. Everything I've read mentions 3-sided leaves, and the leaf on this one definitely doesn't have 3 sides. It looks identical to the E. Oxypetalum I ordered.
Had it in a very small pot till last year, and Sowandsew, I didn't even have it in ordinary potting soil. I used a cactus mix.
Nightbloomer, thank you for your advice. It did look like it needed repotting. How do you train it to get tall??
Thank you again, and I appreciate ANY suggestions anyone has on the care of this plant!!!! 'Mare

You would just have to keep tying it up to vertical supports. It would best be suited to a short wide trellis.