Landscaping can create a large impact even on a small project like this one. In later projects I'll show some modifications to this scene, but for now, here is how the basic landscape has been prepared.
First apply a thin layer of artist's spray mount adhesive or pva (white or craft)glue. Spray mount adhesive will not create the dense plastic barrier to future landscaping that pva glue can create. If you think you will want to add more plants in future, use spray adhesive instead of white glue.
Once the adhesive is applied, and while it is still tacky, apply a thin layer of fine grey/beige railroad ballast and fine aquarium gravel to the glue layer. Press it in place on the surface of the florist foam with a craft stick or the back of a spoon. Press the gravel firmly so that it sets in to the foam layer.When you have the ballast/gravel applied as a base, Dab a small amount of white glue on the bottom of a piece of reindeer moss and use fine tweezers to insert a few pieces of moss against the base of the foundation. You can also add a few tufts of long grass using railroad tall grass, folded in half with a bit of glue applied to the fold before you insert the tufts into the florist's foam.