I took this picture halfway through planting the flower beds, so you can see what's going on under the plants. Since the last picture, I have built little retaining walls from 5mm foamcore, filled the beds with some scrap polystyrene foam, and punched holes into it with an apple corer. Two coats of black acrylic, then a heavy drybrush of my ground colour to bring out the tiles.
The plants are from an aquarium plant ball, and they pop off on little cores that fit those holes. A bit of hot glue, and we're away. I think this looks quite decent, and it certainly fits with the 'Imperial Urban' theme I've got going on here. So. Happy :)