If you do decide to use real dirt here's a tip for you. BAKE IT first. By this I mean get a old pan cake pan, or a cheap aluminum roaster pan, and put your dirt in it. Put it in the oven at 325 degrees for 1/2 hour, then remove, and let it cool. This will kill off anything nasty hiding in it. Also do this with sand. After its cooled run it through a sieve/ strainer to get the bigger pieces out.If you have a dollar store or the equivalent of such, just buy a cheap one. Put the contents into a container, and mark it as fine, coarse or what ever size it is. Another thing you can do is find a old blender to chop up leaves to make clutter for the ground. A real old trick to making grass is to dye saw dust. Put it into a container, add water, and food coloring dye, mix well then let the water evaporate. You can also control the color by how much coloring agent you use. When dry once again sift it out, and store it in a container. To adhere it, use a diluted white glue. You want this the consistency of skim milk, mix it about 50/59 glue to water, and apply to a small section at a time. If you need more help you can PM me or e-mail me. At the link is a tutorial on adding weeds. http://s8.photobucket.com/user/mercman51/library/Tutorials/Weeds?sort=3&page=1