Why can’t miracle grow be used for autoflower, that you’ve heard? I suppose you mean “the all purpose” plant food, maybe miracle grows with the different NPK rating would work, not that I know, I have been using some on my plants I damaged anyway, but my problem was I believe not mixing it strong enough, was sort of playing it safe, next thing ya know, yellowing leaves.
Now, if ya are talking about not purchasing fertilizers, either chemical or organic liquids, I still believe that “composting” is a cost effective way of making decent soil out of food scraps and other is a cost effect way of not having to buy anything, but you don’t throw anything in the mix that had butter mixed with it(salt), and of course nothing that was salted in general, I stayed away from meats thrown in, besides I always put something on meat that is salty or vinegar, shredding of newspaper mixed in can be good, urine mixed in has high nitrogen(usually mixed with water and added right away to avoid ammonia formation)I did it for years for my outdoor plants, you like have a garbage can(or professional made plastic tumbler), and you put all organic vegetable or fruit waste in it, on top of a fair amount of soil, and mix, maybe add some worms, they multiply fast, for indoor plants, I removed the worms and put them back. I mean, I can think of those systems that make fertilizer “tea”, I mean, I saw youtube videos on this, some nasty concoctions of manure “water”. But yeah, urine mixed with plenty of water before adding is “nitrogen” addition, from what I understand, but I aint been desparate enough to use urine, other than peeing in mole holes, you see, moles hate human urine outside, they generally go after worm, maybe bugs, if one has an abundance of worms.
I myself will eventually get back into “organic gardening”, especially for marijuana, its the all natural way with compostings. I suppose getting the right amount of npk could be tricky, I aint no expert, but I bought Jorge Cervantes “The Cannabis Encyclopedia”, and it arrived today, been looking it over, wow, wow, definitely some serious talk on fertilizers, and wow, I just noticed “Miracle Grow” is listed in the book without any serious warnings other than he says miracle grow does not contain magnesium, but I added in Epsom salts anyway to my soil to get magnesium.