You're overthinking this. Hydroponics has different rules than in-ground or container gardening with soil and potting mixes, and other than the fact that fertilizing in the two disciplines uses the same 13 elements, they are worlds apart. It's like trying to take the rules for patisserie and apply them to deep-fried donuts. Both disciplines use flour, sugar, and fat, but in completely different ways.

Do a simple flow chart: Organic or Chemical?

That's all you need to know.

There are people who obsess over the precise temperature of the ice water you pour into pie crust, and there are people who let it go at "meh, cold water". They both end up with nice pies.

Honestly I find it much more intuitive to treat the symptom in the beginning while learning your specific soil and growing condition needs.

All foliage and not flowers?

Too much nitrogen not enough potassium and phosphorus. Malformed leaves or blossom end rot? Not enough calcium and likely too much potassium. Yellowing leaves and no symptoms of potassium or nitrogen deficiency? Up the phosphorus.

Generally speaking--very generally speaking--N is for leaves, P is for roots, and K is for blooms. This is just a useful mnemonic in case anybody ever asks, but all plants need all three elements. Most of the "bloom booster" types of chemical fertilizer is mostly hype.

So stop worrying about it, and just give your plants some food.

There is tons and tons (and tons and tons) of information out there on organic gardening with organic, i.e. non-chemical, fertilizers, not only on the internet but also at the local public library. Rodale Press is the biggie at the library, and Mother Earth News has a ton of online articles.

Start with a soil test. N-P-K are your major nutrients. P and K are pretty stable in the soil, your soil test will tell you if you need to enrich. N degrades into the atmosphere. You'll probably need to refresh it year over year via compost, other amendments, or fertilizer.

There's a host of micronutrients -iron, calcium, zinc, etc. These may be plentiful in your soil, but their availability to your plants is limited by your soil's pH. Your soil test will tell you your ranges and pH.

So, the simple rules of fertilizer are:

  • get your soil tested
  • add P (phosphorus) and K (potassium) as called for in your test results.
  • count on adding N (nitrogen) regularly
  • correct pH if necessary
  • add micronutrients as necessary after your soil pH is corrected.

The last two bullets are very plant-dependent, but most of your normal veg gardens are made up of plants that like it in the middle.

Look up your county and 'free soil tests', most of the US allows folks to get one or two freebies a year and it's going to be way more accurate than a kit.