Plants to trail down a high retaining wall

[annew]

I'm looking for ideas for plants to plant at the top of a 4m high retaining wall, which will trail down the wall, but not invade properties which back on to the top of it. I think there's a metre or so gap between the top of the wall and their fences.
 UK natives would be great but not essential. Any offers?

[Gerry Webster]

Anne - I find Geranium wallichianum  'Buxton's Blue' performs well under roughly similar conditions, sprawling down the wall. Although fairly late into flower it goes on for a long time - it's still in flower now. Before it comes into leaf Erythronium californicum 'White Beauty' does well, although I suppose that  at a distance of 4m it might not be visible!

[Paul T]

Not a UK native, but an Aussie one.... Myoporum parvifolium.  Easily trimmed on the other side as everything is above ground, no underground runners, and it should trail down quite a decent amount.  4m is a long way for anything to trail the whole way from just a top planting.

Depending on how cold it gets during winter (and how much heat the wall stores as a heat bank) then Dichondra Silver Falls will certainly trail a couple of metres.  May be too cold for it with you though I would imagine.