I've got constant access to loads of non-organic eggshells, but I'm unsure of they're safety. In small amounts, I suppose it'd be no biggie, but with maybe about 20 kgs (~45 lbs) ... layered into a sheet mulch bed about 5 square meters (~50 square feet) ... I hestitate. If the sheet mulch bed were to be sitting idle for several months, maybe I'd go for it, but I'll plant straight away.
I have no idea if hormones, antibiotics, and other fun things that get into conventionally grown hens concentrate in eggshells or not. I live in a university dorm, where there is a food court, where I can get all the eggshells I could ever want.
