Plastic Warriors has an article on modeling camouflage netting. The key ingredients in this project are fine gauze and super glue.
Making German East Africa Buildings
Major Thomas Foolery has a photo tutorial on making WWI era German East Africa administrative buildings.
The finished product is quite impressive.
Modeling Tall Grasses
Here’s a photo tutorial on modeling tall grasses, using old brushes.
It looks like you’d be able to get quite a bit of material out of one of those cheap house painting brushes.
Modeling Troy For Skirmish Gaming
While not quite a tutorial, 15mm Wargaming for Fun and Sanity has a great article on modeling a mud brick / adobe town. The build was designed for ancient Troy, but as the author notes, such buildings are extremely versatile, applicable to more periods than you can count — even science fiction.