Microorganisms

Microorganisms are tiny life forms. 


Bacteria, fungi, algae, protozoa, and other microscopic critters (microbes) are all microorganisms found in soil. [The jury is still out on whether viruses are alive or not - but they are considered microbes.] According to Principles and Applications of Soil Microbiology (1998), you will find this many microorganisms in one gram of soil [one-fifth the weight of an American nickel]:

    •    100,000,000 - 1,000,000,000 bacteria
    •    100,000 - 1,000,000 fungi
    •    1,000 - 1,000,000 algae
    •    1,000 - 100,000 protozoa

With those numbers, each handful of soil can contain more microorganisms than there are human beings on Earth. Try wrapping your brain around that, the next time you’re outside pulling weeds!


Most of these microorganisms have not yet been identified, or even named, but scientists at the Earth Microbiome Project, and elsewhere, are working on that. What we do know, in the world of soil microorganisms, is that there are beneficial microbes, and there are microbes that cause us grief.

Microscopic mite (Eric Erbe)

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The Bad Guys

Some microorganisms are disease pathogens that can damage or kill plants. There are bacteria in the soil that can cause fireblight, cankers, and soft rot. Fungi may bring powdery mildew, eutypa dieback or rust to your garden. Viruses can cause spotted tomato wilt, cucumber mosaic, and many other diseases.


The Good Guys

Other microorganisms are critical to soil health because they make nutrients available to plants through the Nitrogen Cycle. Other microbes stimulate plant defenses and reduce stress to plants. Plants also trade the carbon they create through photosynthesis for mineral nutrients mined from the soil by microbes. These networks of beneficial microorganisms can extend a surprising distance from the plant. In the case of giant redwoods, the network of microorganisms that feed the tree can be over seven miles long, in all directions!


Therapeutic microorganisms

One soil microorganism in particular, Mycobacterium vaccae, has recently been found capable of uplifting your mood! This particular microorganism is absorbed through tiny cuts and is inhaled on dust particles, as we garden. Once inside, these microorganisms cause a chemical reaction similar to the effects of prozac. Most gardeners claim that gardening is their therapy. Ends up, they were right!


Microorganisms, like other living things, can be poisoned with herbicides, pesticides, and fungicides. The truth is, we don't really understand all of the interactions between these tiny life forms. Throwing a chemical monkey wrench into what looks like a delicate balance is probably not in our best interest. 


The best way to keep a healthy balance of microorganisms in your soil is to keep the soil healthy. Very often, chemicals cause too much change too quickly. Regularly adding aged compost to your soil is the best way to keep your soil healthy.