As it turns out–and anyone who has played in the dirt for any length of time probably already knows this–what we call “top soil” exists in strata that has very specific and different properties based on depth. In a wild environment, plants take advantage of each of these strata in entirely different ways, but when we till our gardens, we blend these strata together and deprive our garden plants of the ability to use them. Further, by blending these layers, we churn deeply buried weed seeds to the surface and create an environment where broadleaf weeds can thrive.
The damage tilling does is not finished with just the previous effects. Tilling exposes deep dirt, that because of its organic content holds moisture, to the air and sun, which causes it to dry and lose some of its properties, hence the reason so many gardeners have to water so intensively during the summer and fall. In addition, exposing this deep dirt exposes fragile compounds usually protected from oxidization and sunlight to both, causing them to decay into other compounds that are not as beneficial to plants.
As if all of that wasn’t enough, and this idea goes further than even Coleman does, tilling destroys soil covering plants like sort grasses, clovers, and other ground plants that help prevent soil erosion, help maintain a proper ground temperature for growing, help retain water in the soil, and help prevent weed plants from taking root.
Now, I understand that most gardeners will balk at what I am suggesting here, yet the conclusion is almost unavoidable: tilling our gardens (and our agricultural fields) is bad and counterproductive. And, the evidence is all around us.
Find a wild grass area and study it closely. What you will find is an amazing policulture environment containing dozens, and sometimes hundreds, of individual species of plants that all somehow managed to grow together without tilling, fertilizing, herbicides, pesticides, or mechanical watering. They are able to do so because they work together in a meaningful way to produce soil conditions constantly receptive to new growth.
Using a broadfork to loosen ground, in addition to other techniques such as intensive and cooperative planting, help a gardener (and a farmer) come much closer to mimicking natures course than anything machines might be able to do. By using such techniques, a gardener promotes soil health and soil growth without having to add too much to what is already there.
Of course, this kind of technique comes with a price, as does everything: it is far more labor intensive than the garden tiller, yet I cannot help but imagine most of us could use the extra work.