That wall will look great covered with some vine.Really good potential. Where do you live? I live in Florida where the South and West sides of buildings can really be hot in summer.

I can't think of any vines that would actually grow downwards. Some plants will trail but they won't actually cling and head off down a wall. Climbing hydrangea and Virginia creeper certainly would not behave like that. A well established vine shouldn't need irrigation so I'd look into planting at the bottom of the wall. Is there soil there? If not can you make a bed there? To me it looks the perfect spot for an espalier fruit tree or a grape vine.

thanks flora - was worried about training vines to grow down - guess they like heading up towards the sun. I can build a bed - or use some very large pots. Will check out espaliers - will they cling to a wall and grow freely or do they need to be trained? Are they fast growing?

They need to be trained but will eventually form a rigid permanent framework. I have no experience of your climate so it might be time to ask this question over on the Fruit Forum regarding suggested species and varieties. For example, a fig might work but I have no idea if would survive in your area.

Here is a link that might be useful: Fruit and Orchards Forum