First, welcome to the forums.
Secondly, I have dabbled with some model railroading, and the guys from that hobby have really got landscaping down. I would suggest going out to the back yard and getting some sand//dirt and put it in a bucket. Next dry the sand out completely by baking it for a short time on low heat on a cookie sheet. Now, use a sifter to separate the different sized grains of sand. I have a couple different sifters that I use to separate different grades of sand. You should end up with dirt, that actually looks like dirt (don’t worry about the color yet) and not that stuff that’s all the same size that you get at the hobby store.
I would suggest making a base with plaster first and let it dry completely. Then spread white glue over the plaster and then finally sprinkle on the sand. The sifter works great for this too. Let the glue dry, then I usually liberally spray a mixture of white glue and water (about 10 to 1 water to glue) over the sand just to make sure everything stays put. An old windex spray bottle should work great for spraying. At this point, paint your base with the appropriate sand color. You can add washes, and dry brushing if you wish, and few spars plants should be easy to add on.
This is a relatively CHEEP way to make any kind of a base and the results can be very good, but it can be a little time consuming. If you are looking for more ideas, or need some clarification I would highly suggest going to your local Model RR shop, and ask some of the old farts for ideas. Every Model RR shop I have been in has old farts with a LOT of knowledge that are more than happy to help you out.
Good luck,
edog