Yeah, it’s an odd thing: the mined area contains both fireclay and dolomite. The fireclay is as always for all plants. To double-check, I mined a second area of dolomite, irrigated it and channeled over part (dusting of mud on all tiles). This area is immediately adjacent to the fireclay tiles.
Fireclay: will grow anything.
Irrigated dolomite Inside/Dark: will grow any subterranean plants.
Irrigated dolomite Inside/Light: still limited to kobold bulbs, same as the surface.
I’ve never seen this before, just curious if anyone else has. My dwarves are walking a long way to reach the fireclay fields and boozeberries and that’s not good for FPS.