Raised garden bed on concrete. bad?
Im new to gardening, and i have a 6' x 10' concrete slab in my backyard from an old shed that has been since demolished. I would like to build a raised bed garden on this but have the below questions. any advice / tips would be greatly appreciated.
1. how about drainage? do i just put the soil right on top on the concrete? or do i put stone down first to allow drainage?
2. Do i have to worry about anything harmful leaching up into the soil from the concrete slab?
3. do i have to put a plastic membrane down on the concrete slab and on the wood walls of the bed ?
4. how deep of a bed should it be? (will be growing tomatoes, peppers, cucumbers etc)