Do Not Disturb! The Secret to Healthy Soil

In our home, which is sort of a peculiar place, the one magazine that gets read from cover to cover every month is The American Gardener -- The Magazine of the American Horticultural Society. It always surprises us. For example: A recent short piece about the complex relationship between monarchs, milkweeds, soil microbes, and a compound produced on the surface of milkweeds that protects the monarch caterpillars from a parasitic protozoan that lives on milkweed leaves.  Crazy stuff.  If the right microbes aren’t active in the soil, the chemical compound isn’t produced, and the protozoans kill the caterpillars that eat the milkweed.  Depending on milkweed species, and other stuff.  Extremely complex, and research based.  

The bottom line of this article, and of article after article in every garden journal we read, is do not disturb the soil structure.  As gardeners who were raised on Troy-bilt rototiller ads, and who love the feel of finely tilled soil, this seems wrong.  But it’s not.  When you understand how plants live, it only makes sense.  So here’s the deal...

When you talk about plants, you have to start with the sun.  Sunlight hits the leaves of plants, and persuades carbon dioxide and water to become breathable oxygen, sugar and beautiful stuff.  The growing tips of roots ooze out tiny bits of this sunshine-born sugar, attracting soil microbes.  These microbes, the hardest workers in the garden, form a webwork of life throughout the soil. The microbial webwork decomposes plant debris, and delivers those nutrients to the roots that are feeding sugar to the microbes.  The healthier the webwork, the more the plants get fed, and the more sunshine becomes breath, food and beauty.

When you disturb the soil structure, you break up the webwork of microbial life.  This gives the microbes extra work to do before they get back to the business of helping sunshine and plants give us all that good stuff.  Of course you have to dig into the soil to plant a plant, or to sow a seed -- but keep the disturbance to a minimum.

The more I learn about this, the more amazed I am that people, by routinely destroying soil structure to grow food, haven’t all starved to death.  We’ve created deserts and dust bowls, we’ve polluted waters and killed a big piece of the Gulf of Mexico, but we haven’t all died.  Many, however, have died.  

For thousands of years, people of the First Nations of the Andes Mountains planted potatoes in small divots in the ground, and left the rest of the soil intact.  Then, after Columbus, potatoes went to Europe.   When Irish farmers started growing potatoes, British government agronomists were out teaching them the radical new idea of tilling entire fields.

In the middle of the nineteenth century, a destructive airborne fungus found these thoroughly tilled potato fields, resulting in the Great Irish Potato Famine.  Now, a variety of factors caused this catastrophe, but massive crop failure like this never happened in the Andes.  In fact, records from the famine indicate that the Irish farmers who ignored the British agronomists had better crops.  So throw away your rototiller.  Or give it to a scrapper.

But still, some soil needs help.  If you live in a home built in the last 50 years, your developer probably sold off most of your topsoil -- leaving you with compacted clay covered by a couple inches of barely functional soil.  The microbes are still there, but they need organic matter and oxygen, and oxygen needs pores in the soil.  Planting native prairie will fix this.  Prairie root systems go as deep as 15 feet, and then each winter they die back, leaving organic matter and pore spaces.  But it took thousands of years for prairie to build the soil that sent your developer’s kids to college.  You might want something quicker.

Research shows that the first step in fixing a mess like this is to cover the ground with two or three inches of good quality compost -- mother nature’s time release fertilizer.  Then make cracks in the soil that the compost will sift down into; but leave big chunks of soil intact.  You can do this with a shovel. Push the shovel into the earth, pull out a shovelfull of soil, then drop it right back into the hole it came from.  Don’t even turn it over.  Do this until the entire areas is broken up.  Then smooth out the surface and plant.  The bigger the shovel, the better.

Three things happen when soil is broken like this:

  • Compost filters down between the clumps.
  • Oxygen is added to the system.
  • Large portions of the microbial webwork remain undisturbed.  

This way, your free microbial workforce gets right to it -- breaking down new compost, luring roots into new territory, and helping plants convert sunshine into breath, food, and beauty.

And these microbes work weekends, holidays…

Real estate developers are easy to blame for compacted soil, but there’s plenty of blame to go around. A heavy lawnmower on a wet day will do the trick. If your soil is compacted, which prevents the microbes from thriving; it will benefit greatly from the method described above.  Or even from a core aeration.  However, if your soil isn’t terrible, then all it needs is deep rooted native plants, and surface applications of organic matter.  The best, easiest, least expensive, most sustainable method of adding organic matter to your garden will be described in my next blog post.  See you then!