I found some very reasonably priced O-scale trees on eBay (about $1 each), but I somehow overlooked the fact that they have wires for trunks. So I set out to fix them.
Bases are wooden discs from Michael’s with edges ground down with Dremel tool and a hole drilled into the center of each. Then I glued down a washer on each for some extra weight.
Here’s a close up.
Tree gets glued into hole:
Then I sculpted the trunk using cheap air-dry clay (again from Michael’s). To get the effect below, just drag something thin from top to bottom. Make sure the trunk is reasonably thick, or it will crack after drying.
I waited a day before painting. I didn’t seal with PVA, but it’s probably not a bad idea if you want extra durability. Painted dark brown then a quick drybrush with a lighter brown. Flock the base, and you get some pretty decent little trees:
Next batch, I might smooth out the transition between the roots and the base. On these, you can see a bit of a line where they meet. But for a first try, I’m pretty happy.