The Dirt on Soil: How to Keep the Earth Around Your Home as Healthy as Possible
It is the life force of any landscape. It grounds and nourishes plants, and fends off pests and disease. Before you plunge seed or sapling into your soil, consider its health. To get—and keep—yours in top condition, we asked Elaine Ingham, Ph.D., a global expert and founder of the Soil Food Web School, for the scoop.
What Is Soil?
"Most people confuse it with dirt, but they're different things entirely," says Ingham, a soil microbiologist in Corvallis, Oregon. Dirt is basically made of broken-down rocks, while "soil is very much a living thing"—an ecosystem of dirt, bacteria, fungi, nematodes (microscopic roundworms), protozoa, and micro arthropods (like earthworms and spiders). Together, these elements decompose organic matter and release nutrients, a process called nutrient cycling.
What Can Damage It?
Environmental pollution and chemical herbicides, pesticides, and fertilizers. When World War II ended in 1945, munitions companies had an excess of TNT, the explosive in many bombs. Scientists noticed that plants thrived where this nitrogen-rich substance was dumped (never mind that they were weeds), and synthetic fertilizer was born. "Nitrogen will grow a plant—but it won't be a healthy one," says Ingham. Synthetic fertilizer also inhibits the wide range of nourishment needed. As a soluble salt, it dehydrates soil and kills the fungi, bacteria, and microarthropods. You may see quick results from its use, but at a long-term cost: degradation of the ecosystem, and proliferation of disease, pests, and weeds.
How Do I Know If Mine Is Healthy?
If you use synthetic fertilizer, it isn't. If you don't know (new property, say), look around: Is your garden riddled with pests, weeds, and yellowing, crinkled, or stunted foliage, or is it robust? "When a plant has all the nutrients it requires, it doesn't produce the chemical stress compounds that say, 'Eat me!'" says Ingham. For instance, the cell walls of a rose growing in healthy soil are too thick to be penetrated by the piercing mouth of an aphid hungry for its sap. The good news: You can fix soil with proper composting. To dig deeper into your yard's specific profile, or if you have concerns about toxicity, consider testing a sample (see soilfoodweb.com for a list of consultants).
How Can I Improve It?
First, avoid synthetic fertilizers, herbicides, and pesticides. Then feed it with compost. Ingham suggests raking a one-to-two-inch-thick topdressing into your beds every spring and fall. The living parts of healthy soil rely on decaying organic matter; make your own from materials like vegetable scraps, dried leaves, and grass clippings. (For a detailed how-to, check out our compost guide.) You can buy it, too, but be sure to ask an independent nursery near you for reputable, locally produced sources. Whether homemade or bought, it should only ever smell earthy.
Also, create a sound structure. Ingham thinks of soil like a house: Bacteria form the bricks, fungi bind them together, protozoa and nematodes make the hallways, and microarthropods add the windows, aerating the earth. The right makeup increases moisture retention (helpful in droughts), keeps soil full of oxygen (crucial to beneficial micro-organisms), and encourages roots to spread easily and deeply. Also, avoid excessive walking, rototilling, and digging, which can compact the structure, as can rainfall pounding on exposed earth. "Mother Nature never leaves soil bare," says Ingham. Spread mulch (like wood chips) over it—this also stimulates fungal growth, deficient in most gardens—or plant cover crops such as creeping phlox, creeping thyme, and Dutch white clover. These low-growing perennials act like living mulch, surrounding other plants, even veggies.