Remember Deadly Weapon, that when summer comes here in Finland, the heat goes up way too much for most of the Orchidioides section utrics to really grow well. Before I built my highland terrarium, all my orchidioides went into some sort of dormancy during summer. They killed most of their leaves and the ones that remained we're yellow and not healthy looking. And surprise surprise, when the weather cooled down at autumn, they came back from the roots & tubers and started growing really nice. They always followed the same cycle and after getting the leaf growth going, they started flowering somewhere between november-march when the weather is at it's coolest, aka room-temp at night in my growroom got to as low as 16-18 when I turned my heat radiators for that room off. Day temps we're something like 20. And once again, when spring/summer came most of them died back, except like U.nelumbifolia, U.reniformis and U.alpina. With this setup, I was able to flower U.alpina pretty well, U.nelumbifolia grew one flowerscape with 3 flowers and U. alpina x campbelliana gave me a single flower on a single stalk. Let's compare to my new highland setup.
When I built my highland terrarium (It's basically a fridge compressor that has been torn out and put into a terrarium.), I set the night temps to 15 and day temp to 22. To my experience, this is good "all-around" temp for highland utrics. I didn't want to make it a straight 12 at night, as I felt it was too radical change from before. I have all my orchidioides in the same tank, so I wanted to set the temp for an average value, as some might prefer it warmer (like U.alpina), and some prefer it colder (like U.quelchii).
Okay, the setup was built last spring. The first results were shown this autumn, when U.alpina x campbelliana gave me this:
Those are from 2 flowerscapes.
At about the same time, U.alpina 'Pittier Moon' gave me it's first flower:
Also, U.alpina flowered somewhere during autumn. It seems to like the temps a tad warmer than the others, as it flowers either much earlier or much later than the rest of them.
Right now, I have U.nelumbifolia growing 2 flowerscapes, U.alpina x campbelliana growing 4 flowerscapes, U.asplundii has 2 flowerscapes, my own hybrids of U.nelumbifolia x nephrophylla "white flower" are currently growing 3 flowerscapes. As you can see, this time of the year is when most of them flower.
U.praetermissa is still a mystery for me. It's still a baby, but it had 2 quite large leaves this winter. Now they all seem to be withering away, I think it's entering a dormancy. I have very little experience with this species, so I hope it comes back some day.
I don't really know if it would prefer warmer or cooler, the leaves seem to have a tint of yellow in my care, but it might be of too powerful lighting or too low humidity at times.
In my opinion, the easiest species are definitely:
1) U.alpina. It likes it a tad warmer temps, so it doesn't necessarily need a highland setup if you have the terrarium in a room that doesn't get too much direct sunlight during summer.
2) U.nelumbifolia (U.humboldtii). It grows literally in every possible soil mix, from pure sphagnum to sand & peat (although not recommended), and it doesn't care if you grow it submerged or terrestrially or whatever way you think of. In my opinion it grows best with the soil really wet, it loves flooded soil. The only true requirement is high humidity, if the humidity is too low it doesn't grow leaves (or they are very unhealthy yellow) and instead starts growing runners. Runners, all over the tank. It's the most weedy CP I can think of. Not even U.calycifida with it's damn seeds compares. I don't grow U. humboldtii, but I've read it's almost identical in care. If someone has some spare U.humboldtii, please contact me.
3) U. alpina x campbelliana. So easy for me, flowers more than U.alpina in my highland setup. Free flowering, but the most flowers occur during january-march. Doesn't seem to be too picky about temperatures, but if it gets too much over 20, it seems to wither most of the leaves. So it needs some sort of cooling during summer. In my opinion not as picky about humidity as U.asplundii for example, but better keep it on the better side of 60%, as they seem to love high humidity nevertheless.
4) U. asplundii. It's hard to come by and seems to be on the more expensive side on CP selling sites. But it's not that hard to grow. No matter what I do to it, it doesn't really care. It's like U.nelumbifolia, as long as you can keep high humidity, it thrives. It doesn't care about temps that much, for me it always flowers during january-march no matter what temps I give it. I have this one pot with one yellow leaf and I'm like "now it's gonna die", then it grows 2 flowerscapes and I'm beaten.
For me, the best results have come growing it in pure sphagnum, in some sort of mesh pot. It is epiphyte, so I'm not suprised.
5) U.reniformis, U.geminiloba. A little pickier than nelumbifolia, I'm yet to find suitable conditions for them. My clone of U.reniformis absolutely disgusts low humidity, I once took it out of the terrarium during a clean up and the leaves started to shrivel in 10 minutes. It was such a shock, nowadays I mist it like every 3 minutes if I have to transfer it somewhere! It doesn't seem to hate my terrestrial soil mix, bit it doesn't seem to love it either. I used to grow it in similar setup as U. nelumbifolia, in pure sphagnum slurry and a high water level. It grew so thin leaves that they fell over. In peat & sand it's much sturdier, and that's why I prefer it, although it doesn't seem to grow as fast. (read: not as many leaves, but much healthier looking)
U.geminiloba grows well for me. But it's one of the mysterious species too! I grow it in a sort of epiphyte soil mix, but with high water level, just like U.nelumbifolia. It grows a lot of leaves, but the leaves are so small it almost looks like U.nephrophylla. I have no idea if this is because of the temperature (it's almost directly under the cooling plate) or some other reason. Nevertheless, leaves are healthy green and there are a lot of them, so I'm not complaining. Not expecting flowers any day soon though.
I didn't list U.nephrophylla, but it's very easy too, and I think you already know very much about this species. You can add it as 6) It likes warmer temps, so don't put it in highland setup. I have it in both lowland and highland setups, it grows slower in highland (surprise surprise) and hasn't flowered there for me yet. Lowland ones flower occasionally. Humidity is not really an issue, as long as the soil itself doesn't dry. Moderate/high humidity + high water level + good lighting has given the best results for me. Might do even better if the humidity was higher constantly.
Phew, that took some time to write.