I used Woodland Scenics liquid pigment on mine. These pigments are design to be diluted with water so you just brush it on as a "wash" that absorbs right into the plaster cloth.
Its fast, works great dries flat and comes in green , and a variety of earth tones i.e. browns and greys. It gives a nice realistic earthen appearance, after it dries you can add whatever groundcover, trees, bushes, grass etc. Exposed died areas without scenery take on a "rocky" look.
I'm certainly a "novice" when it comes to scenery and the pigments were an easy way to get a "natural look" with little effort.