One of the best things you can add to your garden for growing superb greens is rock dust. Volcanic rock dust, if you can find it, otherwise any rock dust is better than none. (Rock dust is good for all plants in the garden, but especially the greens because it helps give structure to the leaves.)
"Adding volcanic dust mimics glacial cycles which naturally fertilized the land. Since the last ice age three million years ago the earth has gone through 25 similar glaciations, each lasting about 90,000 years. We are currently 10,000 years into an interglacial -- a hiatus between ice ages -- meaning modern soils are relatively barren and artificial fertilizers are needed." (Quote Source)
The addition of rock dust is usually called RE-mineralization, because our soils have become very depleted in minerals over time. (Plants take up minerals as they grow, some more than others, and normal fertilizing doesn't add all the minerals back in.) There are 17 essential plant nutrients; of those, hydrogen, carbon and oxygen are absorbed from the air, while the other essential nutrients (mostly minerals) and water must be obtained from the soil.
However, what really makes a garden work is all the bio-organisms that will convert any and all the nutrients to a form the plants can utilize (take-up via roots). All the nutrients in the world are useless unless they are in a form plants can use.
When we fertilize, we usually add the inorganic nutrients consisting of NPK or nitrogen, phosphorus and potassium, which are called primary nutrients because the plants use a LOT of them. (Bagged NPK doesn't include anything else but NPK and a filler.)
The secondary (mineral) nutrients are calcium, magnesium and sulfur. Those do not always need re-application every year, but they might, so get a soil sample! The third classification is micronutrients (it's what rock dust contains and needed only in small quantities)... more than 50-60 micro-minerals like boron, manganese, zinc, molybdenum, nickel, cobalt and more are available from some rock dust sources.
The colloidal carbonaceous residue known as humus serves as a nutrient reservoir. Besides lack of water and sunshine, nutrient deficiency is a major growth limiting factor.
There is some thought that the calcium and magnesium in the rock dust converts atmospheric carbon into carbonates... which would be essentially sequestering some carbon in the soil, if I understand it correctly.
Currently, I add 2 kinds of rock dust to my garden: Azomite, and Greensand which is mined in New Jersey. I also add biochar sifted from my woodstove ashes, which I inoculate with mild urea or compost tea. All of these components give the bio-organisms something to convert to nutrients for the plants. I know I probably don't build enough humus yet... that is: I don't add enough active organic matter... but this year I plan to use EM-1 (Effective Microorganisms) on my compost and also make Boshaki to continue growing effective microorganisms for my soil life.
But remember, it all starts with rock dust to feed the existing bio-organisms in my soil, which will feed the plants that will feed me.