Roger,
Just a few thoughts that may help. To do your ground cover, have a look at the way nature does it. Dirt first, then some grassy stuff, then some sticks fall on top of that, then some bushes. etc. The best material to use is that gathered from the area you are modelling, and then process it yourself. Finely sieve the dirt from the area. Sprinkle that on a painted on layer of woodglue. Next, use some leaves, grasses, etc that you gathered and put them in the blender. Different conconctions to give diffferent shades of the natural covers. do the same. Sprinkle them on top, over the dirt. Maybe leave some dirt exposed a bit.
Of course you can get the commercially prepared ground cover stuff as well.
As for paints? Try a visit to your local hobby shop for some artist acrylic water based paints. They do come in "earthy" colours. Choose some of the "earthy names" e.g. Burnt "umber", Yellow "ochre", red "oxide" "leaf" green. These colours are made from pigments found in the natural surroundings you wish to model.
Make a very weak "wash" (water the paint down) and daub it all over your scenery. Use a number of different colours (letting it dry between colours) and "splogges" to get a natural weatherbeaten look. Do this
before putting the ground cover on, of course.

Good luck, and we wanna see the piccies of the finished result.
