Nope,
both Milliput and green Stuff are two-component materials, they harden after the two components are kneaded together (exposed to the air or not). Green Stuff is more expensive, but allows for finer details. It doesn't make a real difference, however, if you are doing bases (and not, for example, a heroe's nose).
As for wood - I've never tried, but I often thought about using the wooden thingies you get at Mc Donald's for stirring coffee. They have just the right thicknes for a timber-floor board in HeroQuest size (of course you would have to cut - or, even better, break - them to the right lenght). And they are free
This said, there are lot's of ideas, pictures, and even a few tutorials about basing at both
officialand fan sites of the big miniature (games), expacially Warhammer and Reaper miniatures.
For "natural ground" you could also google around for model railway stuff. These nerds have come a great way since when I played with this kind of thing as a child. You can buy absolute realistic flowers and
leaves, laser-cut in miniature size. And they also have great tutrials about
do it yourself tricks and effects.
(sorry, some links are in German, but you will get a general idea. Surely you'll find similar sites in English)