Beneficial Microbes


There are a number of new products being offered that announce they contain “beneficial soil microbes”.  In the past ten years, there have been  dozens of these products offering the wonderfulness of these microscopic creatures. I’m concerned that people are going to get turned off because no one seems to be leading an effort to explain how these soil microbes function and what good they do.  The danger is that it will all seem like snake oil and turn off people, especially because many of these products are more expensive specifically because they contain a soil microbe package. 


Some products just announce they contain “valuable soil microbes” without identifying which microbes are in the product.  Others offer a list of from 8 to 54 microbes all with names no one has ever heard of.  Going from product to product, the list of benefits for using beneficial soil microbes goes from very vague to fairly detailed and specific. 

Fortunately, some companies have translated much of that scientific mumbo jumbo into simple English and here is a list of the most common benefits accruing from adding beneficial soil microbes to your soil or potting mixes. 


Beneficial Soil Microorganisms will:


Reduce planting and transplanting shock

Increase nutrient availability

Increase and enhance nutrient absorption

Minimize nutrient loss through leaching,

Promote nitrogen fixation

Accelerate cell division

Increase photosynthetic capacity for greener plant

Stimulate root growth and root formation

Improve soil structure

Increase humus levels in soils

Provide increased resistance to environmental extremes (heat, drought, cold)

Kill or control many fungal and bacterial diseases


I know there are additional benefits, but this list is pretty impressive by itself.  Now here is the $64 million question – if my soil is lousy because it is compacted and I use quick acting nitrogen fertilizers and lots of pesticides, will these beneficial microbes have a snowball’s chance of making any noticeable impact?  From my own experience and from some reading I would guess the answer is yes and no.  Yes, if you use these products in the beginning as a foliar spray they will help the plant enjoy many of the benefits in the above list.  No, if you use the products as a drench or a granular top dressing; the barriers to their being successful will often be too great. 


My understanding at the moment is that these products become incredibly valuable and effective ONLY if they are used in conjunction with a program to add significant amounts of organic materials at the same time and eliminate the use of quick acting fertilizers and toxic pesticides.  Unfortunately, most of the products containing beneficial soil microbes now available do not make that observation; I guess because it complicates their story. 


Best I can tell, there is no silver bullet.  The products containing soil microbes will perform as advertised only if we consider them an adjunct to taking proper care of our soil.  That means avoiding activities that compact the soil.  Avoiding fertilizers and pesticides that harm earthworms and soil microbes. And most important, adding organic materials to the soil each year in all gardens, lawns, and under all trees and shrubs.  In five to six years, you will use little or no fertilizer.  You will need to water only infrequently, and your plants will have very few insect or disease problems.  Adding beneficial microbes each year help us get there more quickly. 


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