The first thing to do for your future grows is if you are really interested in organics, make a compost pile or get a plastic composter. Start saving all you kitchen scraps, coffee, egg shells, slimy greens in your refrigerator, etc. Also get yourself a worm bin. Those two things will keep you in food for your plants. Read up on organics. If you want free do you have a farmer that will give you chicken or cow manures?
There is a reason pot costs a lot. It costs a bit to grow so it is kinda hard to do it for free.