Documents: Special Interest: In The Yard:

Benefiting From A Healthy Soil Food Web
by Jim McLain
by Jim McLain


Jim McLain lives and gardens in the Yakima Valley of Washington state. He has been a vender at the Selah Farmers’ Market and has written gardening columns for two weekly newspapers.

Jim is presently the garden columnist for the Yakima Herald-Republic daily newspaper and contributes to the Yakima Valley Master Gardener column that appears in the same newspaper

July 9, 2006

When it comes to gardening about all you really need to do, besides watering and weeding, is feed your plants plenty of fast acting chemical fertilizer. Don’t fool around with slow acting organic fertilizers, compost or dumping other organic matter in your garden. Right?

Well, not exactly. While chemical fertilizers give your plants a quick jolt of nutrients, they do nothing for your soil’s health.

Think of chemical fertilizers as fast food. Most are water-soluble and their nutrients are available immediately. What is not used within a few days, however, will be leached below the root zone and lost. A fast-fix might be needed sometimes, but used too often and in large quantities chemical fertilizers can damage the soil food web.

Soil food web: The food web is made up of all the life found in your soil: bacterial, protozoa, fungi, nematodes, earthworms and a host of other macroorganisms. They feed on the organic portion of the soil—and sometimes on one another. As we shall see, the soil food web is often a microorganism-eat-microorganism world that exists in your garden’s soil. But it’s all for the good of your garden soil.

Bacteria: While some soil bacteria are pathogens, most of these one-celled animals are beneficials. They decompose organic matter and change it into water-soluble nutrients plants can use. This slow process furnishes a continuous supply of nutrients in the small amounts plants need. Additionally, some bacteria species produce natural antibiotics that suppress disease-causing bacteria.

Protozoa: Some protozoa are also pathogens, but most of these one-celled animals that live in the thin film of water that surrounds soil particles are beneficial to plants. Protozoa feed mainly on bacteria, organic matter and other protozoa. Upon dying they release nitrogen and other nutrients ready to be used by plants.

Nematodes: These tiny non-segmented round worms feed on organic matter and other microorganisms, making them important nutrient recyclers. Some beneficial nematodes feed on pathogenic nematodes, keeping them in check.

Earthworms: Earthworms get a lot of well-deserved credit for creating fertile soil. For example, these miniature fertilizer factories are capable of making soil twice as rich in potassium once it passes through their digestive systems. Earthworms also bring up nutrients deep in the subsoil where they can be used. They are also fantastic aerators of the soil. What’s more, earthworms transport beneficial microbes from one part of the garden to another—making them mass transit systems moving microbes to where they are needed.

Fungi: What we see growing above the ground are the fruiting bodies, but that is only the tip of the iceberg. The bulk of fungi exist underground as thread-like hyphae. The innumerable strands of hyphae spread through the soil to help hold it together. They are also important decomposers of organic matter in the soil.

Mycorrhizal fungi, a specialized fungus, colonize the roots of certain kinds of plants and create a symbiotic relationship—one that helps both the plant and the fungi. Their hypae serve as extensions of the plant’s root to reach out for water and nutrients a plant might not otherwise be able to obtain. In return the plant provides energy for the fungi in the form of sugars.

Creating good soil structure: Changing organic matter into nutrients for plants in your garden is not the only job soil microorganisms and earthworms perform. They also help build soil structure. Soil with good structure is composed of about 45 percent minerals, 25 percent air space, and 25 percent water with the rest being organic matter. Microorganisms and earthworms secrete substances that bind soil particles into aggregates, leaving space for water and air to enter. Without healthy populations of microorganisms and earthworms, soil structure eventually collapses leaving little room for air and water to enter.

What this means to gardeners: In order for a healthy food web to thrive in your garden you need to keep your soil continuously supplied with organic matter. In addition to adding organic fertilizers and compost to your soil, you can recycle fallen leaves and yard waste back into the soil on a regular basis. Rather than bagging lawn clippings and sending them to the landfill, leave them on the lawn for microorganisms to recycle back into the soil. In the fall shredded leaves can be spread on perennial beds, lawn, around scrubs and in the vegetable garden where their nutrients will be slowly recycled by earthworms and microorganisms into the soil.

It’s really a win-win situation all the way around when you work with your unseen underground helpers. You can become less dependent on inorganic fertilizers, and in the process you will also keep our landfills from filling so quickly. Everything benefits—your garden, earthworms, microorganisms and you. And yes, even your wallet will be fatter and happier.

  • New Eden
  • Kids Garden
  • Plant a Row Grow a Row