Growing Plants on Rock Walls?

I have some rock walls that I would like to have sedum and vinca grow in the wall. I've tried adding some dirt and in some places that was easy. But the vinca died, which I thought was supposed to be a hardy plant. I've been transplanting stuff for years so this isn't a new thing. Any ideas why it died? My neighbor has it all over her walls and it is beautiful.

Also, and suggestions on how to anchor some other plants to the walls?
Thanks.

By mindy from Terrebonne, OR