An indoor lawn for your garters. Now that's different. But still, think clean and dry. Coconut fiber (plantation soil) is an excellent choice, looks natural, and is good for the snakes. Resists mold, bacteria, etc. but still looks like natural earth. Its also absorbent and feces are easy to clean out since it clumps.

It's no problem at all to keep it damp part time (I do that on the cool side) and it wont mold or grow bacteria if you are diligent about cleaning out feces regularly. Always use your nose and smell the tank daily. There should be no foul smell or urine smell. If there is, you need to spot clean, or replace all of it.

Like I said, try to keep it dry but this is a good material if you need to keep part of the tank moist. It won't mold unless it's fouled by excrement.

Newspaper, paper towel, old tee shirt, or even a Shamwow is better than anything from outside. Dirt is dirt. Ever wonder where dirt gets it's taste and smell? mold and bacteria. Don't use it. Don't eat it either.