Hi Rick,
I'm also an amateur grower like yourself with Dragon fruit. I bought one a few years back and just let it grow in its own pot as I didn't know what to do with it when it has so many prickly spikes. It started to branch out horizontally since I didn't train it to grow up on a pole. It never did bloom, until a few weeks back. I was so excited and tried pollinating it with with a brush between between the hours of 10-11pm which is when the blooms are most fertile. I read that some varieties of dragon fruit are self pollinating, but mine apparently isn't because the bloom later dropped off. It looks like most varieties need cross pollination, so it's good for you to have a few varieties there.
Back to your question about one main trunk verses lateral growth. I've read on some websites that training it to grow vertically promotes growth and helps it to reach maturity faster. At the height of 4-5 ft, it should start to produce lateral branches and at that point the blooms will follow. Besides that, training it on the pole also means easier management since they're
are so prickly besides the fact that they're also heavy. Having their weight supported on a straight trunk will help it from their branches being bumped off. Mine has suffered from some lost "limbs" since I didn't train it to grow on a pole at the beginning. Right now, it's in a big mess and I don't even know
where to begin to help it grow vertically.

Anyway, I've seen some growing dragon fruit successfully and this plant sure needs some TLC. Their blooms are so beautiful and fragrant too.
Well, at least I'm able to see it blooming this year :) Here are some pictures of my dragon fruit blooming. Sorry I don't have info with regards to the soil medium, but have read that since it's a desert plant, it does not require constant watering. I'm sure others who have experience with this plant can chip in with their comments for you. If you have some pictures of your plants to share, that would be nice too.

Hi BF2--

I meant to say that those are great pictures and info. How large is that pot you have yours in? I haven't yet set up a trellis. I was thinking of using a tomato cage, but even the heaviest cage is too flimsy for a big plant. PVC piping is a possibility. I can still drive a metal galvanized pipe down near the middle of the pot, and worry about the laterals later. Hmmm...the plants haven't shown a lot of growth in 6 weeks, but they seem healthy, and there must be a lot of root growth going on below the surface. I'm leaning toward the metal pipe but concerned that it might corrode below the service after several years.

Here are 3 pictures of the cuttings when they were planted back in late May.

BF2, have you considered taking a cutting of your plant 5 grow it more vertically? How much sun does your plant get every day, and what zone are you in? I've read that giving these a fertilizer with more phosphorus will promote blooming, and hopefully fruiting, but I'd like to know why yours doesn't set fruit. Is it really self-infertile?

I just ordered a couple of prickly pear cuttings, after a poor bedraggled plant that has sat untended in a small pot flowered unexpectedly. Here in zone 6b, these can survive outdoors, and produce fruits that are similar to DF in many ways. No staking or hauling them in/out of the house, plus the younger pads are edible. The 2 pods are still looking good 2 weeks on: