Can I farm surface plants on underground sand?

[Sophtopus]

After exposing it to the sun of course, via channeling and then build a roof over it. Or does it have to be some form of clay?

Can enemies break floors?

[Mr.Wiggles]

Sand, Soil and Clay SHOULD be farmable once exposed to either the surface (above ground plants) or cavern spores (underground plants). Once it starts growing grass / moss patches you should be good to go. Glass floor makes the best roof. AFAIK nothing can break the roof/floor to gain entry.

[BlackSmokeDMax]

Originally posted by Mr.Wiggles:

Sand, Soil and Clay SHOULD be farmable once exposed to either the surface (above ground plants) or cavern spores (underground plants). Once it starts growing grass / moss patches you should be good to go. Glass floor makes the best roof. AFAIK nothing can break the roof/floor to gain entry.

Sand, soil and clay do not need to be exposed to cavern air to be able to grow underground plants (dwarf farms), they can be grown on immediately after embark as long as they never have the ground above them removed. They do however need the cavern air to grow underground plants that are good for grazing animals. (e.g. moss)

Glass floors are only for show as once the ground has been exposed once, it is never needed again. As soon as that happens, you can only grow above ground plants there, and they will continue to be able to be grown even if you put flooring over them that blocks the "Light".