Growing Soil
When I was studying geology in college, I kept hearing about how long it took to build an inch of topsoil. One hundred years. A thousand years. Even one hundred thousand years for some soils just to grow a mere inch! In this view, soil was most definitely a finite or limited resource. It was drilled into us how important it was to protect the remaining topsoil we had left. I still agree. We must protect soil.
Yet since my college days, I've come to realize that soil is so much more than it's physical or chemical components. It is alive. Even just since I took those geology classes, there's been a revolution happening quietly in our understanding of soil and just how fast it can grow, regenerate, recover and remediate.
Soil is alive. It is teeming with life. Billions of microbes in just a handful of healthy soil. These underground microbes have many roles in the soil underground. Some microbes - very similar to the microbes in a healthy intestinal gut for us humans - act like an immune system for plants, helping them "digest" or access nutrients they couldn't otherwise reach or consume. Other microbes in the soil break down "carbon sources" like wood chips, straw, dried leaves, and can "eat" through them super quickly. Some of this carbon-rich food is oxidized or gets released back to the atmosphere, while some of it gets cycled as microbes eat each other, breathe, and excrete sticky glues and slimes that create soil structure. It's the rich, sweet-smelling dark soil we know so well that makes our gardens and fields and forests abundant and green.
These beneficial soil microbes work together in compost, in breaking down woody material, or directly with plant roots to grow soil at an incredible rate.
An inch of topsoil in a hundred thousand years?
"Oh, please," say the microbes, "we can do it in a year! Or even less if we are feeling particularly feisty! We just need support: feed us, leave us undisturbed, and support us with plants. Plants are our allies in this process... they leak out sugars through their roots to feed and bolster our numbers while we give them exactly what they need to grow bigger leaves to collect even more sunlight and give us even more sugars."
One of the easiest ways I know of to grow soil is just to add a good blend of biology and carbon sources layered together and kept moist. For example, multiple layers of quality compost alternating with several inches of wood chips will "grow" soil directly on top of asphalt, provided you leave it alone long enough and don't mix or plow or turn under the layers before the microbes have a chance to break down the wood! If you churn it up, you break up the communities of microbes, especially beneficial fungi which need to be left moist and undisturbed to do their work. Soil building can happen in less than a year if you have a robust and diverse biology working alongside you!!
If you see soil clinging in clumps or in a sheath along a plant's roots, you know you have an active soil microbial population underground at the root tips. Yeah, microbes!!
Another technique is "lasagna mulching" to grow soil. Here's an example below of using many different layers with raw materials to grow soil. Substitute other materials that you have available in your area like seaweed, rice hulls, shredded paper, coffee grounds, chopped up weeds or grass clippings! The soil inoculant listed in the recipe below could be a high quality compost, worm castings (aka: fancy name for worm poop which is loaded with beneficial biology), handfuls of soil from an area you know has excellent, sweet-smelling soil like a forest or established garden, a diverse biological powder or mix you buy, or the leftover substrate from growing mushrooms.
Another technique farmers use regularly to improve the soil is with plants or "cover crops". A cover crop is basically a plant cover used to grow or improve the soil. Common ones used by farmers are peas, vetches and clovers (they fix nitrogen), radishes (temporarily suppresses weeds and taproot breaks up compaction), rye and oats (help with nutrient excesses, build soil structure, and suppress root nematodes), buckwheat (fast growing summer crop that can also be used as a mulch), and SO many others... Any plant technically can be a cover crop, although farmers often use a specific set of plants to help them achieve certain results.
For backyard gardeners, I am a fan of growing a wide mix of plant varieties that can also be eaten. For example, a mix of beet greens, spring radishes, wheatgrass, lettuce, peas and other greens is a great way to grow awesome soil biomass underground while also growing leaves you can harvest and use in a salad, stir fry or smoothie. Many "weeds" technically can help you also achieve this goal and many are edible too. Some of my favorite edible weeds being violets, dandelions, purslane, chickweed, lamb's quarters and amaranth. Many "weeds" (do we still need to call them weeds if they are so useful?) even have higher levels of certain beneficial nutrients and overall nutrient density than our more domesticated varieties. Fast-growing blends of edible and nutritious greens can be a great option for the "in between times" like early spring or fall or grown in between taller summer crops. Once I am done harvesting or the plants are getting too tough or tall or likely to go to seed, I cut them down to the ground level, leaving the roots in place to break down on their own and feed the soil microbes. Many times I will lay out the chopped up top portions of the plants down as a soil cover (essentially growing my own mulch!) to also feed the soil microbes and maintain moisture for longer in my soil. Less watering, anyone? Yes, please!
Sometimes it's not enough just to support the underground soil food web. Sometimes we have to actively remove things that are harming them. As I mentioned above, disturbance can truly harm these communities and stall out the processes for soil building. Churning up the soil unnecessarily, leaving it exposed on the surface or adding chemicals (ex: fungicides don't just target "bad" fungi, but all fungi, even our beneficial soil building ones!) are all ways that can hinder the soil biology and degrade our landscapes. Another completely non-intuitive way to break down soil is the use of synthetic fertilizers... think Miracle-Gro or other bright colored, easy-to-dissolve fertilizers. These fertilizers cut off the connection plants have with their root microbes, create acidic conditions that drive away soil life and can prematurely degrade or age soils so they hold less nutrients and water in future. Then why do we use them so extensively in agriculture? They do work in the short term, but at the expense of the life and quality of the soil over time. Using chemicals and fertilizers was part of an old paradigm - which made sense in its time - but did not take into consideration the fact that soil is alive, needs to be supported, and is our ally in growing healthier, more abundant and more resilient crops. This paradigm shift is happening in agriculture already, and it is one that gives me create hope as it becomes clear that prioritizing soil health is better for the farmer, the crops, the land, and is more economically viable. I truly believe "soil health" is the next revolution in agriculture.
So the next time you are walking in the woods or along a driveway that is teeming with plant life, give a nod and a smile to these plants silently pumping sugars into the web of life at their root tips. Ponder on the incredible forms, colors, and creatures that are breathing, moving and building soil at our feet. Soil building can happen completely independent of us humans... yet if we worked together... if we aligned our actions to support those of our underground neighbors instead of hindering them... just imagine the gardens we could grow, the bounty we would harvest, and the chance it gives us humans to be part of something bigger than ourselves.
