Nutrients

good answer by numbers.

7.1%/8.8%/12.1%/6.8%/4.3%/5.8% Whoops, that's what i've been doing lately. At about 1.4EC overall concentration. Again, that's only for a soilless/hydro context. I'm around 1.3EC by mid flower, but above all else, i react to symptoms. My preconceived notion of what should be is secondary.

Depends on the type of fertilizer. If the ingredients require microbes to break them down before they can enter the plant, it's a different ration than ingredients that are 100% plant ready the moment they dissolve into water. A good ratio will work on 95-99% of plants. It's something that you can accomplish. Marijuana plants aren't picky. It's just that some can put up with esoteric mixes better than others. It's alot easier to say the plants are picky. A picky marijuana plant was likely created from a shitty selection process by the breeder, lol. That's a silly trait to pass down on purpose. I regularly run 5-8 different strains - no clones - all the time and pull from the same reservoir. I have no fears of issues, because they don't happen too often and when they do it's incredibly minor and isolated to a plant or 2, if i run into some incredibly bad luck. There are definitely better ratios to use. If your ratio doesn't work well for nearly all plants, keep adjusting until it does. The plants will dictate the adjustments, if willing to listen to them. 7.2% / 7.9% / 12.6% / 6.4% / 4.5% / 6.1% N/P/K/Ca/Mg/S in soilless/hydro it's 1-1-2 for NPK and 4-2-1 for K-Ca-Mg You can see i've deviated from those generalizations. I probably give too much P, but it's tied into my Ca levels and doesn't cause an issue. I'm probably thowing a small chunk of P down the drain. These starting ratios are rough guidelines. No matter what you must read and react to the plant. What 'should be' doesn't fucking matter, lol, just what is. As vege growth ends (not at flip but when stems stop elongating and no new leaf growth), I drop N 10-20%, but the plant still needs most of it. This still requires some minimal read/react to the plants but the type of adjustments i make are tenths of a gram of fertilizer per gallon - 5-20ppm here or there. Soil is a whole nother can of worms, but the same general concepts apply. The difference being the ingredients for soil nutes often need microbes to break it down before it can even enter the plant. So you need a proper 'inventory' exiting in the soil, proper cultures of bacteria to break it down at a rate that sufficiently supplies the plant. This is why you see much higher EC values for soil grows than for soilless/hydro.. a good chunk of that EC can't even enter the plant, which is why the plant isn't sick from such overall high levels of nutes. You've also got to familiarize yourself with how much nutrients is in your soil and how much to supplement and to slowly increase that supplementation over time to maintain critical levels of nutes around the roots as the pre-charge in soil is used up over time. so, it's a question that depends on the ingredients used. I don't do soil grows, so i can't help you with specifics. if in soilless, get the hydrobuddy app. even in soil tracking your ppms of each nutrient over time can be enlightening. it's less precise info with soil, but still highly correlative data - if you stick with same soil mix, hydrobuddy tells you consistent infromation over time.... you'll easily be able to relate the symptoms you see to diminishing levels of nutes over time and when to pre-emptively amp it up to avoid any symptoms.

There is no best ratio. Autoflowers don't have a long veg period so there is no need for major amounts of nitrogen. All cultivars feed differently so it will be a guessing game on the amounts NPK they will need throughout the grow.