Passiflora 'Snow Queen', when planted in the ground, reaches a height of 8 metres with a spread of 2 metres, and that's a single plant. You've got three of them all planted in a container that is only trough or window box sized, and this is why they're not growing properly and 'drying out' - they don't have sufficient root room. As time goes on, you will see more and more leaf loss from the bottom up if they are left in there. You don't mention whether they actually flowered or not either, but I'm not seeing much evidence to suggest they did. This plant can be grown in containers for a few years, but to get reasonably good, healthy growth from even a single plant, it would need a larger deep pot, say 12 to 18 inches deep by at least a foot square.
In order to keep the plant/s going, you will need to move them into larger containers - that would mean cutting back the topgrowth, but if you successfully manage to retain sufficient root material for each, they will grow again quite quickly, although if you're in the northern hemisphere with chilly winters, not till next spring will you see good regrowth, followed by plenty of flowers. Note that although this plant is technically evergreen, in areas where winters are quite cold, leaf loss may occur.