^I agree totally. Right when I transplant, is right when i would start feeding them if I were to keep them in the same sized pot, instead of transplanting. What I was trying to say, is that a 1 gallon pot with FF soil won't need any ferts until you have a good sized plant. Age doesn't really matter, so the new guys can't really say "okay, mine are 3 weeks old, time for some fert", most don't realize that it's the size of the plant that matters, not the age. I see some 4 week old plants that are like 6-8" tall(untrained, in one gallon pots, for example) and they start nutes because they are over that 3 week period that is commonly recommended. They don't realize that the plant basically has only used about 10 days worth of nutes, because it's growing slower than normal, and is not typical of a normal 3-4 week old plant. Then they burn the hell out of them, or borderline overfert.lol
I've found that FF soil will sustain a plant until the roots have filled the entire pot.(if they get watered thoroughly each watering) Not rootbound, but filling the pot nicely. Then it's time for nutes.
(yes, I'm loaded and babbling, so bear with me.lol)