I hope you find a way. My area is a little winter warm than yours and I can not grow them here. Al

Bougainvilleas are killed when we have a cold winter (zone 16). Maybe you can find a climbing rose without thorns. 18 inches is awfully narrow.

Trachelospermum jasminoides is one of my favorites. Both for its clean looking foliage and the fragrance. Would need some support to climb.

Look around your neighborhood to see what your neighbors are growing. I was in Sacramento yesterday and saw at least two bougainvilleas in the downtown area. They are more visible in the summer, of course.

I have grown bougainvillea in Chowchilla and in Fresno very successfully. Barbara Karst, San Diego Red and Purple Queen are the ones I've grown and they've all done excellent for me. Purple Queen can grow into an unruly thicket if not pruned and controlled. In cold years, they will lose foliage, but come right back as soon as it warms back up. In average winters, they will bloom right through winter (for me.)

You don't mention what the winter lows are in your area...but the purples are known to be hardier than the reds. I live in a 9b area, canyon near Los Angeles, with temps down to 17F (2007) and most years I get a few periods with 26-28F lows. I have a 30 year old red bougainvillea and 28-30F doesn't faze it much, but lower than that will kill off the stems/vines. They always grow right back from the roots. Last year we had three 24F nights, and all the woody and green vines died, but by March there were 10 new ones 4-8 feet high/long. And that's normal, the new vines grow back very quickly.

I'm always looking for the Royal Purple variety since I've read that's one of the hardiest...and the flowers when backlit are very pretty. For a first try you should stay away from the lighter colored ones.

Whatever you get, I'd suggest protecting the crown and roots(in the winter) while it's young, just to be sure. And be prepared, in the spring after a cold winter, to prune out all the dead wood. That can be a pain because of the thorns, but then you have a working bougainvillea from March until the first real cold weather. Mine had lots of red flowers until the cold weather we had last December(24F) and that killed most, but not all, of the vines.

I just looked at the plant, there are still 4 or 5 live vines up against the house, and they have nice green leaves. One of the vines has a lot of new leaves (not green yet) popping out, but it's been a warm winter down here since the cold December period.

I agree with that strip seeming very narrow for bougainvillea. If it does live, you're either going to be spending your weekends pruning it (they get new, usually large and unpredictable, regrowth quickly after pruning) or it's going to slice and dice anyone attempting to walk down that sidewalk.

Thought I’d check back in on this thread and see how it went with the bougainvillea in Sacramento?

You don't have much space between the wall and the sidewalk. I wouldn't plant anything with thorns.

Have you considered planting a vine on the other side of the wall and letting it eventually fallover to the other. It might be easier to take care of. And would also be less-heavy looking.