Well - unless it's possible to improve the drainage and soil, then any plants you put in there will drown, so large containers would be better by far.

Is the wall part of the house (or next door's?) Ivy isn't a good plant for house walls, as it can lift coping and roof tiles.

What direction does this wall face? That will make a diffenrnce in what you can grow.

And if this is a house wall other than yours you will need the trellis to be freestanding not attached to the wall.

Thanks. It's a garden wall and doesn't get full sun all day and of course last week it did rain most days so maybe I could just try another bucket of water nd see how well that drains on a sunny day. The soil round here is fairly heavy so I suppose I could fill with a lighter mix? Thanks again for your help.

How much sun (in hours) does it get? That will make a difference in what plants will thrive there, always supposing you can deal with the soil issue. Clematis and roses, for example, like a rich soil. Roses thrive in clay! One foot depth wouldn't be enough for the roots of many plants, if any..

Roses need half a day's sun, most Clems. grow if the roots are shaded and their heads are in the sun...some even prefer a more shaded position. 'Nelly Moser' does - her flowers fade in full sun.

I have a feeling that you'd be better growing your climbers in very large containers from what you've said so far.

I agree with Spritzhenry

I'd say half sun half shade. I need a few plants as it's a long wall but now completely trellised so I think I'll try both options and see what happens as I don't want too many containers. As it happens I would like a climbing rose so I'll try that directly into the ground. There is one around the corner against a house which is right on the pavement, so it must get enough water even though the ground is ashphalted. Thanks again for the advice.

Good luck with it. :-)