It differs from state to state in Germany. Where I live I can spend one night in a tent out in the wilds where I want, but if I spend it without a tent (hammock, tarp etc.) I can spend as many nights as I want out there.
People generally don't give a fuck tho, I constantly meet people who camp out with tents and all that. Worst thing that can happen to you is someone calls the police who will tell you to pack your tent, but they can't make you leave, since you are free to roam as you want.
Only problem that may arise is if you enter a privately owned piece of land, but even then the owner can only make you leave his property if he hasn't marked his property with a fence or something similar.