I would try this question in the Container Gardening forum here on GardenWeb. My gut reaction is that it's going to depend on what vine you intend to grow, and whether the vine is an annual or a perennial.

how high do you need the vines to grow?

how often do you want/plan to water up there?

i've been reading as much as i can on the container gardening forums, and i think this is what another, more experienced gardener might say. growing in containers is a balancing act. if you use a large pot for young plants and fill it with a rich, water-retentive soil (i.e. most potting soils), you might be hurting it more than helping it. gravity can drain a lot of water out of soil in a container, but not all of it. the rest of it only drains through evaporation or if the plants uses it. this is why gardeners traditionally caution against over-potting. over-potting in a rich soil really is typically unwise, but many plants can do perfectly well if they're "over-potted" as long as it's in the right growing medium.

however, since you're talking about a balcony, i'm guessing you'd like to use the smallest containers you can to avoid crowding the space. i can't speak to every vine out there, but i've definitely seen morning glories grow very well out of a typical window box planter that's only 8 or 9 inches deep and wide. in such a situation, richer soil is okay because enough healthy plants should be able to use the water up pretty quickly, though you still might consider getting them (whatever plant you use) started in flats.

whatever you decide to grow, make sure your balcony will provide the right kind of light and other conditions for the plant. if you grow annuals the soil can be refreshed each year, but if you choose to grow perennials, research a long-term soil mix that can last several years. many gardeners find that repotting vines that are already trained on a trellis can be a bit of a nightmare.

This post was edited by shady_10b on Mon, Aug 18, 14 at 11:53