As I write this, the craft stores are already putting the 'harvest season' decor onto the shelves. So I picked this pack up at the local dollar store:
These are garishly colored, and will work fine for sci-fi terrain.
The items have a glossy outer skin, and are often studded with woody stems.
Use a sharp hobby knife to slice the gourd into two parts. Now we can see that the inside is styrofoam. Slicing the gourd like this will give us two terrain items that provide cover.
Or you can slice the gourd the other way, and get one tall piece and a shorter piece.
I chose to put my gourd pieces onto bases. These pieces are very lightweight, so I went with a base that was equally lightweight – shapes cut from a foam-plastic egg carton. I used craft white-glue.
To give everything a more sci-fi appearance, I applied a wash of purple ink, deliberately making it drippy. Let dry thoroughly. Add more if needed.
The gourd pieces weren't sliced perfectly flat, so there are some gaps where they meet the base. I filled this in with Textured Stucco Crack Repair. Let dry completely.
Then paint the base with your preferred 'mud' color. Mine is a cheap craft paint, Americana Mississippi Mud. Let dry.
I then applied terrain glue with a paintbrush, and dredged the pieces into my container of green flock.
The final step was to give everything a spray of matte clear. I was a little nervous because spraypaint can cause styrofoam to melt, but fortunately, the spray didn't penetrate beneath the surface.
And here is a 28mm zombie-fighter posing among the finished sci-fi terrain.
I suppose there's no reason you couldn't do something similar to create fantasy terrain.
You can see how the different shapes and heights will impact game play.
Some of this terrain might even be dangerous!
When the vehicles can go no further, the troops will have to proceed on foot…