Cultivating Healthy Soil

ealthy soil teems with life. Millions of species and billions of organisms—fungi, bacteria, protozoans, nematodes, microarthropods, insects, and worms—are the foundation of what can only be described as an elegant ecosystem, one in which plants play a symbiotic role. In order to have a successful, productive garden you must care for all living things in it: not just the fruits and vegetables themselves, but also the soil that nurtures them.

Soil Science 101

It’s a difficult world to observe, the layer of earth in which we garden. In fact, the majority of critters that live in soil remain unidentified—in part because they are so numerous and diverse. (It’s been estimated that there are one trillion microbe species on the planet, of which fewer than .001 percent have been identified.) Yet we know they’re there, performing the incredibly important job of processing soil into rich humus. They feed on one another and other organic matter then excrete and decompose, which generates nutrients and builds the soil, giving it structure.

Plants are part of this process. Roots actually exude materials that attract beneficial fungi and bacteria. Some of these feed the plants directly in exchange for the food plants provide them. Remarkably, fungi can even extend a plant’s roots—growing from its tips out—further into the soil to help the plant more easily obtain water and nutrients.

I find the science fascinating, as a gardener and as an integrative physician intrigued by the gut microbiome. The trillions of microbes that take up residence within us can greatly influence our health. What happens in soil is actually a mirror of what happens in our gut. The exchanges between soil, bacteria, fungi, and plants mimic those that take place in our intestine between our mucosal lining, microbes, and the food we eat.

Taking all this into account, we can see that the fundamental task for gardeners should be encouraging a flourishing soil ecosystem in which plants naturally thrive, while playing a vital role in maintaining life for other organisms. As organic gardeners and farmers often say, we should “feed the soil, not the plant.” Yet, conventional gardening wisdom still touts caring for and feeding plants above all. As a result, many of our soils are actually inhospitable to plants, lacking the biological diversity that is so essential for them to live and prosper.

The State Of Soils Today

The concept of organic gardening, with its focus on soil health and natural growing methods, is not new. Chemical fertilizers and pesticides are actually the new concepts, and unfortunately they’ve become the norm over the course of the twentieth century. Yes, when you put inorganic fertilizer in soil you give the plant a flush of food, but you create a plant dependent on that chemical rather than on a natural, living cycle—and you’ll have to keep feeding and feeding. Ultimately, these synthetic amendments and insecticides kill the complex ecosystem that defines healthy soil, setting it on a path toward becoming a useless, sterile plot.

So, then, why did we start using them? To make a long story short, our so-called agricultural advances began to ruin the soil: Our plows compacted the lower levels of the soil profile, causing anaerobic conditions that bred pathogens. We also depleted soil fertility by over-farming. But instead of returning to time-tested organic methods, we developed chemical “solutions” that only harm the soil further as well as our waterways and health. This accelerated after World War II, as large-scale nitrate factories built to make bombs were converted to produce nitrogen fertilizer.

5 Steps To Soil Success

Fortunately, in a home garden you’re in control, and there’s much you can do to build a thriving soil ecosystem. To create healthy soil:

Synthetic fertilizers and pesticides kill beneficial organisms and encourage potentially harmful pathogenic activity. They also undermine our health. As we’ve established here and in previous pages, organic is the healthy way to grow. There is a plethora of soaps, oils, and herbal products on the market that can effectively and safely repel or destroy unwanted pests. You can also introduce beneficial insects like lacewings, praying mantises, or ladybugs in your garden to do the dirty work for you. Learn much more about natural alternatives to pesticides on page 50.

Put materials in the soil that feed the bacteria and fungi that are beneficial for your plants. Good options include kelp, fish emulsion, and manure. Just don’t use fresh manure, as its relatively high nitrogen content will dehydrate or “burn” your plants—this is especially true of fresh chicken manure. Be careful of what some companies sell as “organic” fertilizer. Often they still use inorganic salts of sulfur, phosphorus, or nitrogen in their products. If you use kelp, purchase it dried (liquid kelps often have sulfur or some other preservative). You can easily make your own fish emulsion by taking leftover fresh fish and puréeing it in a blender with some water.

CONTAMINANTS IN THE CITY?

If you live in a city, you may want to give some thought to possible soil contaminants before you start to plant.

Urban soil contamination is a growing concern, prompting an investigation by the Johns Hopkins Center for a Livable Future. Researchers there conducted a survey to find out what city gardeners knew about the soil they were using for planting and the risks contaminated soil may present. While acknowledging the benefits of city gardening, the team identified a potential for exposure to heavy metals, petroleum products, and asbestos in soil.

The survey findings suggest many city gardeners recognize the importance of knowing what the garden site was used for in years past, but don’t have the information or expertise to determine their risk of exposure to contaminants that may be present in the soil.

That risk isn’t related only to your personal exposure while gardening but also to the chemicals that might be taken up by the plants you grow for food. This risk is magnified among children, who may play in contaminated soil or eat vegetables grown in city gardens, as their smaller bodies and immature immune systems make them more vulnerable.

Good compost can host lots of beneficial microbes; learn how to make your own on pages 20-22. You can try worm composting, too, sometimes called vermiculture. Worm castings are among the best foods for plants and soil—after all, worms are part of a healthy soil ecosystem. If you can’t make your own compost, purchase a high-quality option: It should have a deep brown-black color like that of coffee grounds but not be totally black (this means it’s anaerobic, or devoid of oxygen, and is probably not good for plants).

I’m glad that the Johns Hopkins team put together an informative booklet—Soil Safety Resource for Urban Food Growers—that includes information on the sources of contamination, how to investigate the past uses of a garden site, and how to test the soil for contaminants (a Google search on the title will take you to a link to download the booklet as a PDF).

Learn as much as you can about your plants and what they really need, especially in the context of your particular climate. Know your limitations. Don’t try to grow things that will struggle to survive where you live, as these plants will attract pathogens, making it more difficult for the other fruits and vegetables in your garden to survive.

For a more comprehensive look at the care and feeding of healthy, living garden soil, there is a great book by Jeff Lowenfels and Wayne Lewis that explains it well using nonscientific terminology. It’s called Teaming With Microbes: A Gardener’s Guide to the Soil Food Web.

The best way to find out about the past uses of your plot is often simply to ask people in the neighborhood. You’ll also want to determine what adjacent land was used for—if there was a gas station, factory, or chemical spill, you might want to think twice about whether to put in your garden. Another good source of information is Sanborn Maps, which has collected building information since 1867 on more than 12,000 U.S. towns and cities. Some of these maps are available free online, but you may have to purchase more recent ones.

The Johns Hopkins booklet also contains information on soil testing, which usually involves buying a kit, collecting soil samples, and sending them away for analysis. The testing companies typically test for lead and other common toxins. In some cases, results may reveal that levels of contaminants are too high to grow food. Even if your designated plot gets a clean bill of health, you won’t know for sure if some less common contaminant is present, which is why knowing the history of the land’s use is crucial.

I hope those of you with urban garden plots find they’re contaminant-free and that you will enjoy growing your own food organically in the city as much as I do in the desert.