Well they work on their own timeslines :) I had to cut down a tree about 6-7 years ago. The leftover stump at the base couldnt be removed without major excavation due to the elaborate root network. That stump has attracted all kinds, sizes, shapes and colors of fungi over the years and they are still busy working on it.
It already is a selling point used by many companies, primarily those targeting marijuana cultivators. "Photosynthesis Plus[1]" is a one such product. I have used it to grow both tomatoes and pot. It does not replace the need to use fertilizer (or compost, etc.) so at least for the home grower, there is no cost savings. At scale it could allow you to use less expensive types of fertilizer or something, I am not sure.
Theoretically it helps to break down organic matter into forms more readily bio-avialible to plants. In my experience I'm not sure I've noticed much difference, although I did see some mushrooms popping out of the side of one of my fabric pots once.
Products like this should be looked at with the same skepticism as "Audiophile grade capacitors" and such. If you want to smell the absolute worst stench -- like a transcendentally rotten smell -- I'd definitely recommend paying $20 for a bottle of germs at your local hydroponics shop.
Marketing BS aside, myorrhizal associations[2] are pretty fascinating, and relatively understudied.I enjoy the analogy sometimes used of it being "the internet for plants[3]."
There already are some product like this. At least for small scale gardening. Not sure about cost difference since I do not buy fertilisers.
I've already used it for about 40 tomato plants. But not sure if it really works (or at least that particular product). Will have to try with some control group next time.
