Garden writer Jim McCausland pens this review.

Imagine a garden where microbes do all the work, including feeding, watering, and fighting insects and diseases.

That garden is the one you have now, and you can make it work even better if you know how its underground parts function. In the same way, you can make your own body work better if you know how it uses microbes in some of the same ways.

Most of this came as news to David Montgomery and Anne Biklé when Anne decided to grow vegetables in their Seattle garden. Bad soil—lifeless glacial till—stood in the way. Anne’s husband David, a geomorphologist at the University of Washington, understood the problem because he had just written a book on topsoil depletion. But could the soil be repaired in less than geologic time?

Anne thought so, and started by mulching the taupe-colored earth with leaves, coffee grounds, and wood chips, supplementing it all with compost tea and worm castings. In about four years, their soil’s color shifted to dark-chocolate brown, its texture opened up, and fertility skyrocketed. Their soil now produces robust vegetables and ornamentals without chemical fertilizers or pesticides, and the landscape has become a lush space that attracts birds, beneficial insects, spiders, and a vast underground microbial network.

The more Biklé and Montgomery understood the elegant interrelationships involved, the more they wanted to share it all. Their new book, The Hidden Half of Nature (W. W. Norton, New York, 2016; $26.95) is a natural history of the garden’s underground life. It interweaves parallel histories of soils, plants, and human health, introducing major players along the way that shape the way we understand gardens and wellness today.

The book is practical. For example, Biklé and Montgomery advocate no-till gardening. They never dig organic amendments into their soil because they don’t have to: worms, earwigs, and beetles do initial breakdown and mixing; mites and springtails continue the process; fungi deconstruct the cellulose; and bacteria, amoebae, paramecia, and nematodes do the rest. Worm tunnels aerate the soil and channel water and humic acid deeper into the earth.

When roots move into this biologically rich topsoil, they develop symbiotic relationships with underground microbes. Plants start by pumping carbohydrates produced by photosynthesis into the soil around their roots. These carbs feed the bacteria and fungi that convert other nutrients from minerals and organic matter into forms plants can use.

Such microbes make up a huge percentage of soil organic content, fixing atmospheric nitrogen, carrying water, buffering drought, and fighting insects and diseases. Biklé and Montgomery eventually realized that “the secret to promoting life above ground was to promote life below ground.”

Biklé has a personal stake in this research, both as a public health specialist and as a cancer survivor. In her own battle with disease, she and Montgomery studied the human immune system, which is as dependent upon microbes in the digestive tract as plants are dependent on microbes in the soil.

They learned that when soil life is depressed (as by chemical fertilizers), plants lose nutritive value. And that moves up the food chain: the authors say that “micronutrient malnutrition . . . now affects far more people than caloric malnutrition.” The percentage of people with chronic and gut-related illnesses has also increased radically as chemical fertilizers have replaced natural fertilizers.

By connecting these microbial dots, Biklé and Montgomery started seeing the natural world in a way that has changed the way they eat, garden, and live—and in the process they’ve given us one of the year’s best books on gardens and health.

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