IMO, that is too small a pot to grow one passiflora successfully, let alone 3 different ones! Passiflora caerulea is a big, robust vine and big, robust vines develop big, robust root systems! You could confine it to a 5G container for awhile but it will not be happy long term in such a small container. The others are not quite so rampant in their growth but still need sufficient room for development.

Were you intending to grow these all as houseplants? Unless you have a heated greenhouse or a conservatory, I doubt you will see any likelihood of flowering or possible fruit production. Temperate zone plants, even tender ones, tend not to do well when grown indoors.

Thank you for your answer! :)

Aw, there goes my plan for a super big ass tower of passifloras XD

Well, I'm planning all of them as houseplants, I've seen many people grow them successfully indoors and even get them to flower, so I'm optimistic :) But I am a bit puzzled, cos the photos I've seen are of flowering passifloras in waaay smaller pots than I've planted mine in (I mean real people with real photos, I'm not talking about photos from flower shops) and I've read conflicting articles. Some say the root system is rather "horizontal" and quite shallow, others claim that their roots can grow really big and deep, so I'm not sure who to trust on this one...

Either way, I guess I'll plant them all separately and see what happens! :)

Kathrin, Incense and caerulea are large, aggressive growers if left on their own. I have a caerulea var Constance Eliott that completely covers a 25' sabal palm tree annually. I tear all the vines down in the spring, but by fall it is covered again. Incense will behave similarly if given the opportunity. That said, you can cut them back--they're vines after all--to maintain plants at a desired size. Their roots also grow aggressively, so they'd likely become rootbound within a couple of years. And these two types send out roots both horizontally and vertically.

Those potted passiflora you see are *probably* fed a steady diet of nutrient-enriched water. There wouldn't be much soil in those pots to hold fertilizer or moisture, so this can be compensated for by steady addition of low amounts of liquid fertilizer in the water. The roots never dry out, but never get waterlogged, either. This is a setup many nurseries use, and it keeps trees and other plants green and healthy despite the fact they don't have enough root mass to support that large a plant under normal circumstances.

A bigger problem for your plan is the indoor part. Both caerulea and Incense really love bright light. They adore hot, direct sunlight. You can probably keep them alive if you have large, south-facing windows they can live in, but if not, you'll need a lot of supplemental lighting if you hope for them to flower. Smaller decaloba types of passiflora are much better suited for use as indoor houseplants, but even these will want more light than your average houseplant.