A chap in Terrington (either T. St John or T. St Clements, I can't remember which), in north Norfolk is a world authority on miniature conifers so I went to see him and his delightful Japanese garden. He has more or less retired from the nursery business but still raises a few plants and has a substantial stock of truly miniature conifers. Naturally, they cost more than small young conifers that will ramp off on you and soon be useless but you can have a deal with him. I bought a load of plants and encouraged him to promote his stock within the garden railway fraternity. He told me that several garden rail people had rung him but that over many years, I was the only buyer!
While there, I chanced to see an amazing plant that creeps along the ground and over rocks and looks just like mounds of grass. I believe it is a mossy saxifrage but its name is Scleranthus Uniflorus,. There is a Diflorus variant which is bigger and coarser. I bought one plant and split it up into five and this picture is of one of those pieces, still with us after a few months of winter. It produces a flower head which self seeds all over the show, including in its own mat giving it a flowing moundy sort of appearance but you could keep it flat and it will spread as far as you like. I fancy it growing over some rocks that I have used to form a cutting so that it comes to look like grass ion top of a cliff edge. It is as tough as old boots. I got some seeds of it from Plantworld and several germinated but the frost got them. However, when the spring comes, more will germinate I assume.