Now, back to that other bit of plastic, the one I thought I could tear apart and make trees for 15mm sci-fi? Well, it turns out that like most plastic foliage, the parts snap on and off, and the individual pieces look like this...
It's not too stiff, but not so floppy that it'll fall over. To my eye, it looks like the kind of bio-engineered trees that would be planted to raise a planet's oxygen level.
So the rest is simple: Make a lump of Model Magic, stick some pieces into the lump, let it dry, flock it, seal it, and...
...from one plastic plant, a forest!
Construction note: Try to keep a spine on the piece to keep it from warping as it dries, and don't make the edges too thin.