You might have to sacrifice a few flax or barely trying to make it work. Check what biome you're in as you walk around the area since the minimap might be a little misleading. You'll know the moment you plant something if you can or not.

I made my plains farm right on the edge of the biome and I don't think I've had a single plains monster come mess with it. I didn't even build anything, just tilled the area, planted flax and left.