Ronnie, the fastest way is going to be to add fungi to the soil. Fungi are the real building blocks of soil life, and everything else depends on them. Not bacteria, they can be transient in the soil and they don't form the long webs of interconnected hyphae that fungi do. Not nematodes or arthropods, although if you do import a soil sample from elsewhere you will increase their diversity by doing so. But when you inoculate with fungi, you are setting a buffet table for all the other soil organisms out there, and if the buffet is open, they will come.
Now Orange County is not the easiest place to find fungi this time of year, but if you know where to look, you can find some. Try the overwatered lawns and landscaping at large shopping malls. Since they overmulch and overwater, it's easy to find fungi there. Even if you don't see any
mushrooms, you may be able to dig down an inch or two into the mulch and see white strands (hyphae) and you have found what you are looking for. It doesn't matter what kind of mushrooms you find, plant pathogenic fungi generally don't make mushrooms, it's the soil dwelling decomposers that do. A lot of what you will find in Southern California in the summer are of the
Amanita genus, excellent decomposers and soil builders, but extremely toxic and dangerous to mammals. If you want to be picky and only inoculate your soil with edible varieties of mushrooms, you can (a) use only store bought mushrooms or (b) take a
course in mycology and become an expert and hunt up your own.
How exactly to inoculate? That brings up an important word to know -- totipotent.
Definition of TOTIPOTENT: capable of developing into a complete organism or differentiating into any of its cells or tissues <totipotent stem cells>
Mushrooms are totipotent, meaning that if you whiz mushrooms in a blender, separating all the cells, each individual cell in the resulting smoothie can develop into a hyphae producing colony. If you then drench your soil with this smoothie, you've inoculated it with millions of cells and soon the hyphae will be growing, decomposing the organic matter in the soil and providing food for myriad numbers of other soil critters. Professional mycologists tweak this method by adding things like starch and agar, trying to find the optimal (lab) medium for growing fungi, but you don't have to be high tech like that. To get your soil health started all you need is a blender and an eye for spotting mushrooms.
It forms relationships with other microbes, thrives on disturbance, is a sun lover and very hardy.
