outdoor soil mixed with things like perlite, vermiculite, coco bark, peat, Compost can work well depends on the outdoor soil and what you mix it with and I like to wet my soil mix and heat it in the Oven to kill anything that might be in the outside soil. Sandy loam soil is the best to work with, but if your soil has salts or other things that isn't good for the plants it could hurt the plants too. I mix all my soil now and I think it's so much better then any store bought soil.