I'll be creating a raised bed in my back yard for the main purpose of growing root vegetables like potatoes, onions and carrots. Could someone advise me on type of lumber, depth of dirt and type of soil.

I've been told that carrots and maybe potatoes like sandy soil. Seems like you would need 2" thick lumber for a sturdy raised bed, maybe cedar. Is a depth of 6" okay or would 10" be better?

Thanks for any suggestions.