How wide is it? It looks too narrow for any shrubs. Your giant headed Hydrangeas are a poor choice. Maybe shade tolerant climbers on the fence, low growing perennials or ferns, but anything taller will droop forward. Plants grow towards light. If there's a fence behind them they'll lean away from it, unless it's very sunny.

That is very narrow. How deep is it? How long is the area shaded and at what time of day?

Yes, it is very narrow -- too narrow for shrubs or large perennials. The suggestions for climbers is a good one. You can put some annuals in front of the climbers, something like geraniums or heliotrope that can take some shade (but not too shady). Some trailers would like nice spilling over the walls.

Some clematis are fairly happy on a north-facing site, and have a relatively small footprint. Your other options might be trailing and scrambling alpine types such as saxefrage, sedums, plectranthus, vinca minor, campanula pocharskyana ,small ferns (adiantus)

I think your best bet is something climbing that is being aggressively trained to the trellis. Either that or ivy or Virginia creeper.

Both ivy (always a bad choice) or virginia creeper cling to solid surfaces; they are not twiners around a trellis.

A fan trained Morello Cherry or a shade tolerant rose like Albertine might work if there's decent soil and enough of it. But personally I'd probably remove the trellis and just use ferns. Some grow three feet high in a season and some are evergreen.

I think I would plant annual climbers and also hang some art/decor on the wall for added color and interest. I agree with mxk on the trailers too.

:)

Dee