I need a plan for building soil fertility [View all]

We've lived here 10 years, and we've never fertilized the garden.

There are hella supplements out there, and I was thinking that this winter, I could add supplements to the garden about once a month to replace lost nutrients. I'm thinking about giving it the full spectrum of nutrients, and adding stuff to build the soil.

I want to go mostly organic/natural. (I have worm castings, but they're going on the flowers.)

Has anyone ever done this? If so, what do I use?