Are Soil Probiotics Effective for Your Garden? Find Out Here!

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4/19/23, 8:58 PMBuying Soil Probiotics (Microbes) - Are They Beneficial, Effective or Nonsense? - Garden Mythshttps://www.gardenmyths.com/buying-soil-probiotics/?fbclid=IwAR1XSQoAgDhQZUS1Cpsj4VX7oQX_Gv-syLx3eaSOcah7mqiq50YqdZxpq602/18Soil Microbes – A Quick DiveThis section alone could fill a book and in fact it does take up a significant part of my book, SoilScience for Gardeners. Here is a quick summary.The two key groups of microbes in soil are bacteria and fungi. There is no doubt that these arecritical for both soil and plant health and a gardeners job is to grow more microbes in soil. If theydo that, they solve all kinds of gardening problems.Some facts:One gram of soil, the weight of a paper clip, can contain 1 billion microbes.It is estimated there are a billion soil bacteria species and only 30,000 have been identified.There are 1 to 5 million species of fungi in soil; only a small fraction has been identified.Earth could contain a trillion microbe species, many of them living in soil. We really don’tknow.There is no doubt that existing microbes are critical for the garden and that gardeners shouldtake steps to grow more of them, but is there any benefit to adding them from a purchasedbottle?Microbe Populations are DynamicMicrobes reproduce very fast when conditions suit them, and when conditions are no longeracceptable, they die or go into a state of hibernation, allowing them to wait until conditionsimprove. Population densities change very rapidly.The species that are present at any given time are also very dynamic. If soil gets wetter orwarmer, new species start to thrive, while others die off. Food sources have a great influence onpopulations. Most species can digest sugars, but only a few can survive on the lignin in woodyplants. Oxygen levels and temperature are also important.Science is just starting to get a handle on this, so as gardeners we really can’t tell what we have inour garden at any one time. We also have no way of knowing how to manipulate the populationsto our advantage because we don’t know when and if it changes.The fact that manufacturers of products claim to know exactly which microbes you should add tosoil is quite surprising and should trigger all kinds of red flags. How can they know this whenscientists don’t?Landscape Fabric - Weed BarrierClothHomemade Weed Killer -Roundup vs Vinegar vs SaltEggshells - How Not to UseThem in the GardenDish Soap Can Damage YourPlantsFloating Seeds in Water - Is Thisa Good Seed Viability Test?Baking Soda in the Garden -Hacks that Work and Don'tWorkAre Dandelions ReallyImportant to Bees?Sunlight Calculator - AnotherProduct You Don't NeedWill Gypsum Improve Clay Soil?Corn Gluten Meal - Does it WorkFor Weeds?Is Urine Safe to Use in the Garden?Compost Science for Gardeners is ReleasedThe Myth of Clay Pot Heaters – Do TheyWork?Measuring the Number of Microbes in Soil –The Microbial BiomassLomi Electronic Composter – Are The ClaimsTrue?Is Lead in Garden Soil Killing You?Is Bone Meal Good for the Garden?Top Posts & Pagescredit Youth & Earth

4/19/23, 8:58 PMBuying Soil Probiotics (Microbes) - Are They Beneficial, Effective or Nonsense? - Garden Mythshttps://www.gardenmyths.com/buying-soil-probiotics/?fbclid=IwAR1XSQoAgDhQZUS1Cpsj4VX7oQX_Gv-syLx3eaSOcah7mqiq50YqdZxpq605/18There is very little evidence that supports the idea that added microbes will prosper and colonizethe soil.What Are Beneficial Microbes?Most academic discussions just talk about “just” microbes, but manufacturers of products like touse the term “beneficial microbes”. Gardeners seem to like the term too. By definition these aremicrobes that are beneficial to plants which includes anything that is not a pathogen. Even if amicrobe does not help a plant directly, it usually helps indirectly, by providing nutrients to soil,or improving soil structure.The term beneficial microbes tells the gardener nothing about the contents of a product – it is amarketing term that is used to make the product seem important.What Are Effective Microbes?The term Effective Microorganisms (EM)was initiated by Dr. Teruo Higa to describe acombination of about 80 different microbes which were capable of improving the decompositionof organic matter. He developed the idea that the right combination of “positive microbes” wouldimprove any media, including soil. The initial product was called EM-1, which contained threegroups of microbes: yeast, photosynthetic bacteria, and lactic acid bacteria.Since the introduction of EM-1, many other formulations of effective bacteria have beenproduced by a variety of manufacturers. When you buy a product containing effective microbes,you are buying a combination of microbes that the manufacturer considers important.Marketing departments and gardeners routinely mix up the terms, beneficial and effective.What Does the Science Say?A lot of research has been done in this area and some studies show that bacteria or fungi addedto soil improves soil and plant growth, while many others show no effect at all.The problem with many of these studies is that they don’t design the experiments to separate thecontribution of the actual organisms, from the media holding them. I have discussed this beforewith compost tea. You can’t compare tea containing microbes to water, because we know the teacontains nutrients that help plants grow. To prove the value of the microbes you have to comparecompost tea containing live microbes to the same tea containing dead microbes. Almost nostudies do that.Many of the positive studies are lab experiments that are not using native field soil. When fieldsoil is used results tend to be negative. For example, when four commercial products were added

4/19/23, 8:58 PMBuying Soil Probiotics (Microbes) - Are They Beneficial, Effective or Nonsense? - Garden Mythshttps://www.gardenmyths.com/buying-soil-probiotics/?fbclid=IwAR1XSQoAgDhQZUS1Cpsj4VX7oQX_Gv-syLx3eaSOcah7mqiq50YqdZxpq606/18to tomatoes growing in field soil containing native populations of microbes, they did not improveplant growth and had limited effect on the native microbe population.When studies are properly designed, most show no benefit when microbes are added to soil.There are some very specific cases where the addition of identified microbes reduce a specificplant disease. There are also well known inoculants like rhizobium bacteria for legumes.However, the science does not support the general idea that adding microbes to soil will improvesoil health.Quality of Commercial ProductsIf you buy some soil probiotics you will get a bottle, or package that contains a liquid or powder.A gardener has no way to know what is actually in the material.Oregon Department of Agriculture has been testing products containing beneficial microbes. “Ofthe 51 products tested for bacteria, only nine met their guarantees. Of the 14 products testedfor Trichoderma, a fungi, none met their guarantees. Of the 17 products containing mycorrhizalfungi, only three met the guarantees made on the product label.” DNA testing showed that insome cases the organism had never been in the product. In other cases the organism was nolonger viable.Remember that probiotics are living organisms. They have to be produced and stored correctly,or the product is worthless.Probiotics in AgricultureIf probiotics worked, agriculture would be the most important customer for them becauseagriculture is driven by profit. Any product that can increase yield will be adopted.A recent discussion, by an industry insider, about the lack of adoption of probiotics in agriculturehighlighted two important reasons why they are not used more.A lack of scientific studies showing they work.Where they do work, they only work some of the time. “For example, in corn, yield increases… approximately 70% of the time. The reality is in a good or even average season, yieldadvantages from a microbial product may be minimal if at all.”Probiotics are only successful when abiotic soil factors such as texture, pH, temperature,moisture content, and substrate availability are critical assessment to determine if they matchthe microbes needs. This is difficult for agriculture, but impossible for gardens.The current science does not support their wide use in agriculture and there is almost noevidence they work in gardens.Do You Have a Microbe Deficiency?Companies are telling you that you need to add more microbes. Why not ask the question, “do Ihave a deficiency?”

4/19/23, 8:58 PMBuying Soil Probiotics (Microbes) - Are They Beneficial, Effective or Nonsense? - Garden Mythshttps://www.gardenmyths.com/buying-soil-probiotics/?fbclid=IwAR1XSQoAgDhQZUS1Cpsj4VX7oQX_Gv-syLx3eaSOcah7mqiq50YqdZxpq607/18How can you measure a deficiency? How can you tell which microbes you have and which onesare deficient?The short answer is that you can’t find this out. Even labs specializing in this kind of testing can’tidentify the microbes you have because scientists have not even named most of them. These labscan give you some general numbers for bacteria activity or fungi populations, but what do you dowith this information?There are no guideline numbers that indicate degrees of healthy soil. No one can test your soiland give you a list of the microbes you are missing.And yet, manufacturers of these products are quick to tell you that their product will improveyour soil. They have no way of knowing this. And you as a gardener have no way to verify thatyour microbe populations improve after applying the product.Perhaps the most important point is that you never have a deficiency because microbepopulations are always at capacity.Probiotics Added to SoilOne of the claims by manufacturers is that they are adding large numbers of microbes and thatallows them to overpower existing microbes, thereby eliminating pathogens and modifyingnatural populations.How many microbes are actually added?I looked up Plant Probiotics by Micra Culture. It was the first one I found that provided thecontents of the product. A 57 g pack is enough to cover 100 sq ft and it contains 20 x 10bacteriaper gram. This adds 10bacteria/sq ft.Lower quality soil contains 10bacteria per teaspoon, or 6 x 10/cu ft.That means the product will add 1 bacterium for every 3,000 bacteria already in the top 6 inchesof soil, assuming all of the bacteria in the product are still alive. I don’t consider that a “largenumber!” Remember that bacteria can multiply very quickly. If given extra food, the 3,000natural bacteria can be 6,000 in 20 minutes. What effect do you think one extra bacterium hason the population? None.Also note that 1 teaspoon of lower quality soil has 5 times as many bacteria as one pack of thisproduct.Have Commercial Products BeenTested?I have researched a dozen different manufacturers to find a scientific study that shows theefficacy of their product. I have contacted manufacturers and asked for their evidence. Mostdon’t even try to reply. I did get this reply, “This is a bacterial treatment. No information waspublished.”7 8 811

4/19/23, 8:58 PMBuying Soil Probiotics (Microbes) - Are They Beneficial, Effective or Nonsense? - Garden Mythshttps://www.gardenmyths.com/buying-soil-probiotics/?fbclid=IwAR1XSQoAgDhQZUS1Cpsj4VX7oQX_Gv-syLx3eaSOcah7mqiq50YqdZxpq6011/18February 3, 2022 at 8:39 amHere you go:https://www.frontiersin.org/articles/10.3389/fpls.2017.02204/fullhttps://academic.oup.com/femsec/article/94/7/fiy094/4999898?login=truehttps://link.springer.com/article/10.1007/s11104-017-3199-8Three meta-analyses covering several hundred studies.ReplyRobert Pavlis says:February 3, 2022 at 7:55 pmThe first link is a meta data study that looks at the use of probiotics(biofertilizers) in Agricultural settings. They looked at the aggregate result of yieldsand found a 10-20% increase in yield. There conclusion is that “Our results givestrong indications that microbial inoculation is more successful in dry regions.”Almost none of the studies were done in North America – most were done in Indiaand middle east.– there is no indication of the number of studies that found no increase in yield – justan aggregate average.– yield increases in non-dryland conditions were under 10%.– there is no indication of the source of the inoculants – they might be commercialproducts, or laboratory cultures.– the study looked at N and P levels but not at other soil improvements– no indication of changes in microbe populations in soil– higher organic matter levels had lower yields.– lower yields with increased irrigation.– no indication of soil condition before inoculants were appliedIt does show that some inoculants are useful in agricultural settings, in certainconditions, which was acknowledged in the post. It says nothing about the use ofcommercial products.The problem is trying to take this information and extrapolating it to gardens, whichtend to have higher levels of both organic matter and water. It is unlikely that any ofthe studies were done in garden-like settings. We don’t know if they were done withcommercial products that are available to gardeners. The actual microbes involved aregrouped into larger categories making it impossible to know which organisms wouldbe the best choice for gardeners.The second study is a meta data study looking at the use of biofertilizers for maize. Itconcluded that, “Yield increases tended to be slightly higher and more variable ingreenhouse studies using field soil than in the field” and “We found greater efficacy ofAzospirillum spp. and lower efficacy of Bacillus spp. and Enterobacter spp. under fieldconditions. Surprisingly, biofertilizer strains with confirmed plant-growth-promotingtraits such as phosphorus solubilization, nitrogen fixation and phytohormoneproduction in vitro were associated with lower yields in the field than strains notconfirmed to possess these traits. These results indicate the need for a novelbiofertilizer development framework that integrates information from native soilmicrobial communities and prioritizes field validation of results.”

4/19/23, 8:58 PMBuying Soil Probiotics (Microbes) - Are They Beneficial, Effective or Nonsense? - Garden Mythshttps://www.gardenmyths.com/buying-soil-probiotics/?fbclid=IwAR1XSQoAgDhQZUS1Cpsj4VX7oQX_Gv-syLx3eaSOcah7mqiq50YqdZxpq6012/18In short it says, there are some cased where there are positive results and some thatare not positive – more testing needs to be done.The third link is also a meta data study looking at Plant growth promotingrhizobacteria. The search criteria was for “BPGPR and drought and rhizobacteria anddrought”. It does conclude that “that PGPR are highly effective for improving plantgrowth, with a greater effect under drought for above ground traits. ” “The majority ofthe observations in this meta-analysis were conducted in the greenhouse” – not fieldstudies.As mentioned in my post there are some special cases that gardeners might consider.But how do these results relate to gardens that are rarely in drought condition becauseof access to water?A review of plant growth promoting rhizobacteria had this to say, “Under fieldconditions, other external factors come into play and the ability of soil bacteria toelicit positive effects on plant growth can be impaired and so that the effects ofapplying specific PGPM can be variable (Nelson, 2004b). The plant rhizosphere iscolonized by microorganisms from the soil and the seed. The determinants of soilmicroorganisms are based on properties such as C and N availability, organic mattercontent, water availability and pH (Bossio et al., 1998; Drenovsky et al., 2004; Garcia-Pausas and Paterson, 2011) as well as biogeographic patterns including soil type andseasonality (Kristin and Miranda, 2013). Hence it is necessary to develop strategiesfor effective inoculation methods, so that bacteria of interest gain advantage incolonization efficiency over others. Product quality, compatibility, and stabilitydetermine effective colonization and consistent performance of the inoculum underfield conditions (Lee et al., 2016).”https://www.frontiersin.org/articles/10.3389/fpls.2018.01473/fullWhat is clear from this is that there are many variables that affect the efficacy of anyproduct and that these variables have yet to be worked out.ReplyPierre says:February 4, 2022 at 4:53 amYes, it’s complicated. And I agree that commercial products cannot betrusted blindly. All I am asking is to not ignore the overall conlusion of the currentstate of scientific knowledge on probiotics, which is: on average, they do provide asignificant positive effect on crop yield (some more than others), also in non-drought conditions. As for gardens, I think it is worthwile testing your garden’sstate of soil health (surely, Robert can tell you Canadian services that conduct suchtests) and, besides other, more important management practices, try out someprobiotics, especially if you encounter a disturbed soil or if you are interested inreducing synthetic fertilisers, pesticides and/or irrigation.With “try out”, I mean observe if you can actually see a positive effect. The positiveeffect can be yield increase or maintaining yield while reducing/replacingfertiliser/pesticides, or improved stress tolerance of your crops. And if you do tryout probiotics, let us know here!At the end of the day it comes down to ones mindset/philsophy: Sustainablegardening doesn’t need much external inputs, but if you are used to quick fixessuch as mineral fertilisers and pesticides, why not try solutions that are less