Proof of Life: There May Be Mold in Our Soils

Posted at May 13, 2011 | By : | Categories : Articles | Comments Off on Proof of Life: There May Be Mold in Our Soils

If you find white mold in a bag of our potting soil, don’t think it’s spoiled like moldy bread.  Consider this white webby material the ultimate proof of life. It is an undeniable sign that our potting soils are perfectly blended to create a bio-active root environment.  Even while that bag sat at the garden center, a great deal of activity was going on in our living soils, and the mold proves it.  This is a rare opportunity to actually see one of the invisible organisms that contribute so much to organic plant health.  Such tiny living things are literally a web of life key to all fertile soils.

Molds appear only when the bag is warm and moist inside.  Such conditions actually make the mold grow on the surface of the soil because it thinks it’s underground.  Once the bag is opened, sunlight and drier air forces them back to their invisible subterranean status.

This mold is a saprophyte, one of many that are naturally present in forests and  bogs.  When we harvest the bark and peat for our soil mixes, the molds living inside the organic matter come too. Their role is key to the ongoing decomposition of organic matter in the wild that continues within our soil mixes.  These organisms also feed on the organic fertilizers added to our soil products making them more available to plants.  Their interaction with fertilizers is directly related to why organic plant foods take more time to reach optimal levels than synthetic ones.  In fact, patches of mold can be thickest around pockets of organic fertilizer.

Saprophytic molds act much like beneficial insects do in your garden.  When aphids attack in the organic garden, bio-control is provided by hungry ladybugs that feed on them.  If you use chemicals to control the aphids, you lose these beneficial predators too, leaving the door open for future infestation.  This is why we do not sterilize our soils.  Sterilization may yield a disease free environment, but in a short time the disease organisms will return without the saprophytes for natural control.  Naturally occurring beneficial microbes in our potting soils carry this complex yet natural balance into every container you plant.

Be aware that not all potting soils will foster saprophytic molds.  Insufficient nutrient content and low amounts of fine organic matter in poor quality soils cannot support them.  Plants grown in such mediums will lack the many layered benefits provided by a diverse population of soil microorganisms.

Today’s backyard gardener will find that our saprophytic-rich soils are the most optimal growing medium available.  As the molds do their job over time, you can be sure that this soil is just growing richer in the process.



In 1945 J. I. Rodale wrote Pay Dirt, a book that began the organic gardening movement by introducing soil as a living thing filled with countless microbes that are destroyed by agricultural chemicals.  Well over a half century later radio host and organic gardening guru Jeff Lowenfels published Teaming With Microbes: The Organic Gardener’s Guide to the Soil Food Web, which furthers Rodale’s work into a twenty-first century soil manifesto.  This book is everyone’s guide to understanding just how important these invisible organisms are to the plants we grow, and how easily they can be destroyed.

Our potting soils, soil amendments and hydroponic growing mediums are literally teeming with life, which explains why an invisible form sometimes chooses to show itself.  Any bag of our soil that is warm and moist enough can literally break out in white webby signs of busy microbe activity.  It’s because the basis of the mix is natural cocoanut coir, peat and compost blended with varying amounts of organic fertilizer and worm castings.  Together these offer microbes the ideal environment to flourish.  And with those containing our mycorhizzae, they’re doubly active.

To learn more about this fascinating microscopic life in soil, catch Jeff Lowenfels community radio program online or find out when and where to listen in Alaska here.

Click here to see his book at and read what people are saying about this excellent introduction into the miracles of microbes.

Visit Jeff’s own web site and read his columns here.



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