I searched this board for Pumpkin Stems, and it seems like no one has posted on this topic yet. Thought I would share my experiences here.

I found a picture within a fantasy RPG book of a Hobgoblin Guard Tower. I thought about it for a while, and I came up with using fairly straight Pumpkin Stems as the "tree" base: they look great w/o any paint; they're soft, easy to drill out/cut; they tend to be inexpensive, especially if you take them from a Jack-o-Lantern you already bought for Halloween.

I used bamboo skewers to make the sharpened sticks around the base of the towers, as well as using them as the pole steps up the trunk; I used them to form the platforms, and the railings around the platforms, as well. Simple, really. I painted the skewers with a dark brown urethane-stain, followed by a matte clear coat. I added lichen between the sharp poles of the base, to simulate buckthorn, to prevent creatures from just walking through them; this also channeled infantrymen through the singular opening, making defense straightforward.

Originally, I used peel-n-stick vinyl floor tiles for their bases, but these warped, severely, within months, so I replaced them with 6" squares of MDF, solving that issue permanently. I painted the bases with PVA Glue, followed by an application of sand, for texture. I added some "stones" to create a pathway, which dressed them up nicely.

I made a bunch of these. I tried to use the straightest Pumpkin Stems I could get, but they typically curve in the gardens, as they grow. I made the best that I could with what I had.

More photos can be seen on my blog page:
scroll down for Project #2.
I ordered a bunch of Pumpkin Stems off of e-Bay, as I could not deal with buying a dozen pumpkins! Quality and size vary, so be careful in what you buy off of e-Bay: make sure you check/double-check their sizes. I ordered a batch that were tiny, ended up using them as smaller "tree trunks" that had to be cut down around the massive trunks used for the Towers.

Cheers!