I started adding scenery to the upper level of the layout about three weeks ago. Once all the webbing was in, I added the hard shell using used dryer sheets soaked in hydrocal. One to two layers is all that's needed. Once dry, I painted on a thick coat of flat latex paint, that was close to my dirt color, and sprinkled on sifted dirt that I picked up off Hwy 285 just west of Denver a few years ago. After I let that dry overnight, I then added more dirt to cover any spots that needed it. I do this by spraying the ground with "wet" water while adding the additional dirt so it sticks, then I use a syringe to cover it all with diluted white glue. With the glue still wet I add different colors of ground foam. I then add lots of rocks and some other foreground materials and glue them down using the same technique.
I still need to add a bunch of forest floor junk made from sticks, leaves and other stuff from the backyard that I'll grind up in an old blender. The rocks also need more color and some vegetation, and mostly I need to add trees. But for now it's fun to see a train run over something other than plywood.