Indoor Crossbreeding Farm Dilemma

[Kage_J]

I'm currently working on crossbreeding (specifically for Terra Wart), and the Tekkit Wiki suggests crossbreeding in darkness to prevent unwanted crossbreeds from growing. So I carved out a basement under my base with no windows or light sources, and the crops grew, but of course, a butt load of zombies spawned in the room and trampled all my crops.

Does anyone know a good way to crossbreed in darkness without hostile mobs spawning and ruining the crops/potentially breaking down the door and infiltrating my house? This might be a really noobish question, but I am a noob, so the help of more experienced players would be much appreciated. :3

[BLAZE MkIV]

Half slab the floor so they don't spawn.

[Kage_J]

Aha, that seems to be working quite well. I didn't know about the slab thing...like I said, quite new to the game. X3 Thank you!