There are a great many fertilizers and soilless mixes that promise to add microbiological agents (mostly mycorrhiza) and charge you extra for these.
I’ve never bothered with them because a) container crops are so short term and you’re not using soil so the addition is useless. You’re not going to create a soil food chain in a soilless mix that’s going to enhance your plant growth.
And I don’t worry about them in my garden either. Frankly, a handful of compost (even if you buy it) is going to contain far more than what you can find in a fertilizer jar. Not to mention that different microbiological agents colonize different soils in different concentrations. (Lots of “different” in there aren’t there) 😉 And the price of a bag of compost is far less than anything with “special” ingredients.
Bottom line: It’s expensive marketing and not of much benefit for your garden or containers.
And along comes the Oregon Department of Agricultures’s testing program.
ODA’s Fertilizer Program is the only one in the nation checking on ingredient claims made for microbiological products. The program began testing products claiming to contain beneficial bacteria and one type of beneficial fungi (Trichoderma) in 2013. Of the 51 products tested for bacteria, only nine met their guarantees. Of the 14 products tested for Trichoderma, none met their guarantees. Last year, the program began testing products with mycorrhizal fungi, which form partnerships with plant roots for mutual benefit. Of the 17 products tested, only three met the guarantees made on the product label.
“Many of these products are being sold at a premium price, yet nobody was looking to see if these microbes were actually in the product,” says ODA fertilizer specialist Matt Haynes. “We had anecdotal information that some products had nothing added despite what was said on the label. Once we started looking, more often than not, the companies making these products were not able to back their claims.”
As an example, a one-liter retail container of a fertilizer product that claimed to have both fungi and bacteria sold for $87.50, yet testing did not indicate the presence any of the microbes.