Gem tree farm?

So, I've been trying to get a gem tree farm started. Never really played around with this before. I'm in the cavern layer, as I've got "what a horrible night for a curse" (or w/e it's called) running.

So I've got a room empty of walls. The floor is raw stone. 5 spaces between each planting seems to work. No permanent light source in the room (magniluminescence I"m wearing doesn't count [and yes, I probably misspelled that]). The problem is the moss.

I've tried paint, but that doesn't work; moss just grows on top of it. I can't keep chipping away at moss if I want the trees to grow quickly, because it'll be under the saplings by the time I get out of bed. It randomly spawns rather than spreading from other stone, which means I'm either left with partial tree growth or no grown trees at all.

Dunno how to solve this. How do I get rid of the moss entirely without having to babysit the trees? I figure there's gotta be some of you experienced tree gemmers out there that know a lot more than me, yeah?