Are microbes necessary at all?

I believe that having soil with lots of soil life and organic material in it is healthy and that nature has evolved plants and soil organisms together for a reason. On the other hand, I had a debate with a person not long ago that uses the Mittleider (sp?) method of gardening, and his "soil" (plain sawdust) has no life in it at all as far as I can tell. His plants grow great, produce heavily, and I don't know that anyone could taste the difference between his food and organically-grown-in-great-soil food. I haven't done any type of nutrient testing so I can't comment on that. Anyone have any input?

I haven't heard of the mittleider method, but what does he use for fertilizer?

Soil microbes aren't mandatory when a commercial chemical fertilizer is used, like Peters or Osmocote or a hydroponic fertilizer. Way back in the early 70's, I worked in a commercial greenhouse where the growing medium was a peat moss, perlite, vermiculite mix. Fertilizer was delivered via watering a Peters fertilizer solution. The African violets grew vigorously and were gorgeous.

It is my understanding that one of the actions of soil microbes is to ultimately create the components which eventually become plant nutrients. So if one is not using chemical fertilizer, then microbes are one cog in the nutrient production cycle.

Microbes contribute in may ways, from causing gene expression in plants during times of stress against pathogens, or with symbiotic relationships that lead to the creation of new compounds, to populating plant cells themselves and contributing to our own microbiome as we eat or are exposed to them and the medium they're grown in.
Mittleider is considered a form of hydroponics whereby the growth medium is usually sawdust that absorbs and holds water-soluble nutrients and when given enough sun and regular nutrient feedings plants respond like body builders do on protein shakes. There are also variations on this technique using mediums like sand. The key is a low density medium that affords root growth through air and soluble nutrient delivery that makes for light work on the plant's behalf, but more regular work on the gardener's. It'd be wrong to say hydroponics or Mittleider's method is devoid of microbes as plant microbiome studies show otherwise, however those studies also show a difference in communities of microbes depending on growth mediums and any nutrient solutions.
There are studies showing soil heat treated to kill the vast majority of microbes, as well as sterilised seeds and grown in a sterile chamber using that soil, won't grow.
Also, of all the plant and soil microbiome studies I've read, the most diverse communities result from organic gardens that use dry, green and animal manures and involve plant polycultures of greater number than 16.

Su Ba, he uses regular fertilizer along with some kind of special trace mineral mix he buys from the Mittleider company. He uses small amounts but uses them often.

Craig, I don't know that I would call it a form of hydroponics. He does it in regular raised beds in his yard that are filled with sawdust. I also don't think it is more work than regular gardening. He spends maybe 15 minutes a day and has no weeding, tilling, mulching, or any of the things many people do. He uses a small amount of fertilizer and drags a hose with a towel on the end across each garden once, and that's it.

I still can't get past the idea that soil life IS important and his plants must be missing out on something, I just have no evidence to prove it.

All you have to do is hone in on the dependence Mittleider method is on importing nutrients constantly to see it is not a sustainable or very permie type of gardening. I have run across fans of the technique, and yes they get results. It can look very impressive. However it is heavily reliant on importation of nutrients for it to work. If that is what folks want, they are welcome to it. Me however and I suspect many others out there prefer a more sustainable gardening system.

As for the title of this thread and the question, are they necessary. The answer is depends on what type of gardening you want to do. You can likely get away with a sterile environment but then you would need to do the work of the microbes. Microbes, fungi, little animals, etc all help change the soil into forms that are helpful for plants. Plants in turn also provide necessities to those other life in the soil. A healthy soil with microbes, little animals, and fungi in it can become a self sustaining eco system that keeps renewing itself with little to no inputs. The sterile system though well that is the way big agriculture likes to try do things. Kill anything not the desired crop, and we have seen how disastrous that system has gotten. Constantly needing to import nutrients because they killed the nutrient makers. Constantly worried about disease and pests, because they killed the disease and pest fighters. Can you do a sterile garden, sure but then you need to do the work of all that life that you don't let live in the garden.

Todd Parr wrote:Craig, I don't know that I would call it a form of hydroponics. He does it in regular raised beds in his yard that are filled with sawdust.

I wouldn't call it a form of hydroponics, but it is highly related. The system uses an "inert" material to hold moisture for the roots of plants. The saw dust is just there to give the moisture somewhere to absorb into and hold it until the plants need it. Much like starting plants in rock wool, or similar. The material is just water absorption medium and to give the plant a structure to push it's roots into to support itself.