So . . . this scene also utilizes roots and twigs from plant. The structures in the background were made from chunks of Styrofoam. We sprayed the S-foam with diluted white-glue (PVA). Any harsh chemical, like stray-can paint, will eat away the S-Foam, so if you apply spray paint you can first use latex spray paint as a layer to serve as a barrier, IE,. a primer. Then you can spray normal paint on the surface. A little over-spray can add some subtle colors and add dimension to the scene. If you are going to glue Styrofoam to an other piece of Styrofoam, you really should glue a sheet of paper between the foams and let it dry. If you just put PVA on each side and put them together, it takes forever to dry! Let the paper dry=then add more PVA and then put the pieces together for drying. There is dirt and there is sand. You will start to notice different colors of Earth as you delve into making your sets. This goes for Everything. Making miniatures scenes and structures follows one major rule: This is no such thing as JUNK! You will start to look at all things on the floor, on the garden, in your trash, after you unwrap something from the store in a "different" way. SO many ways to make models with things that no one else would take a second look at once you start! Putting items in the foreground also give your scene dimension. Even things blurry in front of the camera can add 'depth' as well. I keep old cans of paint too. They can be brushed on to act as a primer/protector or provide color to objects. Moss can be bought from Dollar/99 cent Stores to serve as foliage. I spray roots with glue and dip roots and branches into moss to look like trees too. MANY things are available for model railroad scenes at hobby stores, but if you look around, there are tons of things that you can use in their place. (I DO buy things if necessary).
YOU are the master of your set, so keep an open mind! GOOD LUCK!