My neighbor seldom waters his dragon fruit plant in a 5-gallon pot, and it grows many branches and fruits. I cut the branches off when it grew through my fence and I threw them on the ground to compost, but they didn't die, they grew roots. It's kind of invasive and hard to kill.Good luck, I’d love an update at some point on how it’s going.
I did some research on scoria and it’s just lava rock. I picked some up at Home Depot the other day to mix with coco for the dragon fruit. I’m curious to try that mix with something else though and see how well it works. I may try something in a bucket in Spring.