I walk out onto my deck on a clear blue-sky Colorado morning. The surrounding mountains unfold into the distance, enveloped in deep green ponderosa pines spotted with occasional fuzzy looking douglas fir. The landscape is luxuriant with growing vegetation, but it poses an interesting question: how do thousands of trees thrive on such seemingly barren slopes? There is almost no topsoil and very little moisture. When snow or rain falls, it drains quickly through the gritty soil, leaving little trace.

I work this same soil in my mountain garden, so I know it well. Over the ten years I have gardened up here at 7,400 feet, I have had to discover the central mystery of soil fertility – microbes. Life needs life to create more life. The thousands of pine trees surrounding my home depend on microscopic soil fungi called mycorrhizae. These fungi grow miles of tiny filaments that transport nutrients and moisture to the tree roots in exchange for droplets of sap. It is the kind of cooperative and mutually beneficial relationship that exists throughout nature. Plants rely on an intricate ecology of living organisms that live in, on, and around their roots. These organisms, often called the “soil food web,” transform everything available into premium plant food.

A handful of good garden soil contains billions of beneficial soil bacteria — maybe 25,000 different species or more. That same handful holds yards of fungal filaments, thousands of single-celled protozoa, many tiny wormlike nematodes and probably more than a few insects and earthworms. It is a living, breathing, crawling universe in which multitudes of living beings compete, cooperate, eat each other and reproduce. Imagine New York City viewed from a hundred miles up – that is a less hectic place than a teaspoonful of dirt.

It is not easy for the non-gardener to appreciate the beauty of ordinary dirt. Dirt is dirty; it conjures up images of un-cleanliness, of germs and the need for chemical cleaners to keep house and clothes spotless and hands antiseptic. When we reach for the perfectly clean vegetable in the supermarket, we do not think about the soil in which it was grown. Yet without the living dirty world of soil, life as we know it could not survive. We are not so different from those mountain ponderosa pines; we too depend on the soil and its vast colonies of living organisms to feed us.

There is evidence that our fear of dirt is making us sick. Humans and dirt have grown up together – co-evolved. Exposure to the microbes in dirt is a natural part of living. The hygiene hypothesis tells us that lack of exposure to natural bacteria early in life increases our vulnerability to allergies and asthma in adulthood. Recent research shows that a specific soil bacterium, M. vaccae, not only boosts our immune systems but helps ward off depression. Maybe that explains why Mahatma Gandhi put such store in using earth poultices to cure ailments.

If soil can cure, it is itself becoming progressively sicker. Over the last 60 years, US industrial farmers, lawn companies and weekend gardeners have decimated the soil with chemical fertilizers. Inorganic nitrogen and phosphorus, the N and P of bag fertilizers, kill off whole populations of soil microbes. Without these microbes, plants have to rely on the “fast food” of chemicals to survive; plants become addicted.

Furthermore, without soil-building microbes, organic matter cannot decompose into compost and humus. It takes a thousand years to naturally create just one inch of fertile topsoil containing 5% or more humus. Humus is carbon, so fertile soil keeps carbon dioxide out of the atmosphere. Over 50% of all the natural humus in US soil has been depleted because of the use of chemicals. Millions of tons of greenhouse gas have been released into the air from unsustainable agricultural practices.

To care for the soil is a form of environmental activism. When you build a compost pile and fill it with your table scraps and garden waste, you fix carbon and do a little bit to keep the air free of CO2. The body of every tree, shrub, and plant is made of carbon. If only 25% of suburban yards with their patch of chemical laden lawn and trimmed evergreens were transformed into luxuriant organic gardens, global warming would be substantially reduced.

But if you want to change the world, one garden at a time, you have to be vigilant. That bag labeled ‘organic’ on the shelves of a gardening store is often little different from its chemical cousin. To simply substitute so called natural products for chemicals is an example of what Michael Pollan in “The Omnivour’s Dilemma,” calls the industrial organic approach to agriculture. The word “organic” is the newest marketing buzzword; big corporations such as Purina, now manufacture organic fertilizers.

The activist gardener has to reach beyond simple organics to a more expansive vision, a different paradigm. The goal is not only to create the most beautiful, the healthiest and most nutritious plants, it is also to recognize and nurture microbial life. Become a gardener of the soil food web, not just a plant grower. Make a compost heap that heats up to 160F through the action of microbes. Fill your patio pots with compost from a friend’s garden. Plant green manure crops and turn them into the soil. Brew aerated compost tea.

About five years ago, I was turned on to compost tea and the miracle of microbes. My brother John, one of our family of fanatic gardeners, was winning Guinness World Records for giant vegetables using his own compost tea recipe. He persuaded me that my soil was lacking in life; that was why I could only produce average vegetables and sickly perennials. He was right. Once I started brewing and applying the rich brown liquid teeming with trillions of beneficial microorganisms, my whole garden transformed.

Now I enjoy a garden riotous with blooms like those of my childhood in Ireland and Wales. Our vegetables grow lush and nutritious throughout the year. These are the gifts of a soil ecology that grows more fertile and rich every year. I appreciate the tiny bacteria and fungi working hard to feed the plants and the rest of the soil food web. I see that web reflected in the bugs, butterflies, birds, and snakes that make my garden their home. As a gardener, I too am part of the web of life. As Gandhi tells us: “To forget how to dig the earth and tend the soil is to forget ourselves.”