Microorganisms in Soil
- Myths and Facts -
Increase Microbes by Adding More?

Myth #2: Increasing microorganisms in soil is as easy as adding soil microbes (sold in packages or can be homemade) to any soil to increase soil fertility and plant health.

There is some truth and error in the above statement. Find out what the truth is below.

It is true that soil microorganisms are the backbone of organic fertility. Without them, nothing would live. Microbes are responsible for all the mineralization of raw elements in the soil by converting them into nutrients the plants can use. Incredibly, a single gram of healthy soil can contain over a billion beneficial bacteria. Many companies actually sell beneficial microbes that are easily applied to plants and soil.

With microbes being so important, it seems to make great sense to simply increase microoganisms in soil by applying a commercial product containing specific microorganisms or a homemade "organic tea". The added microbes will increase in numbers and activity resulting in healthier plants, right? Not necessarily! In fact, it could make things worse in certain situations.

What is Needed for Microorganisms in Soil to Increase

A simple bedrock truth of soil microbiology is this: The Environment Selects.

"The environment selects" means microorganisms will increase or decline based on the type of soil they are placed in, along with other factors such is temperature, etc. For soil microbes to increase the environment must be conducive to growth. 

Microorganisms are living things and need specific elements for growth. They need:

  • Adequate soil moisture.
  • Near neutral soil pH, preferably between 6.5 to 8. Below 5 favors fungi over bacteria, including many pathogenic fungi.
  • They need aerated soil that is not compacted, water-logged or other potentially anaerobic conditions.
  • Sufficient nutrients, including Nitrogen, Potassium, Phosphorus, and micro-nutrients.
  • Proper soil temperature for growth.
  • But most importantly is the amount and type of readily available organic material - the principle food source of the most abundant type of soil microorganisms.

The Most Important Factor for Success or Failure

The amount of organic carbon, also known as organic matter, will directly influence the increase of microorganisms in soil. The overwhelming majority of soil microbes need organic material as their primary source of food. For there to be an increase in microorganisms there must be an increase in organic material for them to consume.

However, if you increase the organic matter, it will naturally cause an explosion of microorganisms in soil anyway. As the food source increases, the number of microbes will naturally increase.

What About Adding a Specific Microbe to the Soil?

Even if your goal is to provide a specific type of beneficial microbe to your garden or lawn soil, the above conditions still must apply. The conditions must be conducive for growth of the microbes that you apply along with the addition of organic matter. If the conditions are not conducive, the "conditions in the environment (soil type, temperature, moisture, oxygen, etc.) will select" which type will survive and which ones will not.

Is Compost Tea a Good Food Source for Microorganisms

Compost tea is easy to make and increasing in popularity among home gardeners. There are many books providing compost tea recipes. Unfortunately, sugary molasses used in compost tea is consumed rapidly by microorganisms and will provide no lasting affect. Various studies have concluded that compost teas must be made properly and applied in a very timely manner as often as several times a week to have any noticeable result.

Learning how to compost lawn and yard waste is a better choice for long term results. Even better is leaving your mulched grass clippings on the lawn after mowing as an available food source and for increasing microorganisms in soil.


Many organic organizations will tell you to add more beneficial microbes and you are on your way to a more healthier garden. It is as simple as adding fertilizer, but in this case it is microbes you are adding. While it will probably have no harmful affect, making a healthier garden is not always true. Just because they survive in the controlled environment of a bucket doesn't mean they will survive in the more harsh conditions of a lawn.

It is all about balance in nature. Soil microorganisms are subject to the conditions they live in. They will naturally equalize based on the food and nutrient availability. For microbes to increase there must be more organic matter available than what the soil microbes can consume over the year. Since microbes are more active in warm weather, warm climates will require more carbon than cooler climates.

Once the available organic matter is consumed the microbes themselves become food for each other until the level of microorganisms in soil is equalized with the amount of food that remains. Without adding carbon before the additions of microorganisms can result in even lower lower microbe population due higher levels of carbon that would be consumed.

For those wanting to

Let’s view the "microorganisms in soil" study from a different angle. Lets view the recent discussions of applying microorganisms to ocean water to consume crude oil. While the following situation is different, the same considerations and conditions mentioned above for bacteria to thrive on land apply here too. Let's consider the Exxon Valdez oil spill where the additions of microbes were explored to consume the oil:

Quote by Discovery News: "There was an awful lot of hype in the 1970s and 1980s about adding bacteria, and it didn’t really pan out," says Robert Howarth, a professor of ecology and environmental biology at Cornell University who worked on the Exxon Valdez cleanup effort."

Why? While crude oil was the target for the bacteria to breakdown, oil by itself cannot support bacterial life. For life, the microbes needed an increased in nitrogen, phosphorus, potassium, sulfur, etc. You simply cannot add all those nutrients to water without creating other problems.

Added to the problems is that it is simply too cold in Alaska (artic currents, short summers and long winters) to support long term bacterial life of the type needed for fast oil decomposition.

Now, let’s jump to the more recent Gulf Oil Spill: Researchers experimenting with adding bacteria to ocean water in the Gulf Oil Spill offer these similar observations:

"The problem, [with adding additional bacteria] Lee and Atlas say, is that besides oil, the bacteria need other nutrients in greater abundance for their populations to grow". "What is useful is the addition of a fertilizer -- nitrogen or phosphorus," Atlas says… "Leaving the environment’s native bacteria to do their own cleanup might be just as good, he adds." Discovery News [online Discovery Channel News] Friday June 11, 2010.

The bottom line is: Whether bacteria are added to the Gulf to breakdown oil or added to soil to breakdown organic matter and raw elements, for bacteria to live they require other things as well and lots of it.

The same conditions must be met in water as on land. Adding bacteria alone usually will not work for long. They must have additional food, nutrients, oxygen, as well as other elements to increase.

How Can You Get Microorganisms in Soil to Rapidly Increase?

Agri-Gro's Products: Turf Formula, Foliar Blend and Boutiful Harvest Products increase soil microbes that already exist in the soil by 3400% in 24 hours and by 5000% in 72 hours after application. You can't get this with organic teas!

This increase breaks down organic matter, plant stubble, and raw soil elements much faster than nature alone. It delivers nutrients to plants that would otherwise not be available. 

These products are prebiotics that specifically increase root growth and numbers, increase plant health, support water intake, promote beneficial microbe growth and decrease soil pathogens. (University of Missouri/Colombia)

Check out our pages on Proof of How Agri-Gro Products Work

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