The Sacramento Bee
SACRAMENTO, Calif. — The key to a great garden? Look under your feet and start valuing your soil.
“We treat soil like dirt, and they are not the same thing,” said noted soil scientist Steve Andrews, the “Compost Crusader.” “Dirt is the stuff that your nosy next-door neighbor likes to dig up on you. Dirt is the stuff in your vacuum cleaner. Dirt gets on your clothes, the kids, the dog and the cat. But dirt is not soil.
“Soil is a living treasure, an amalgam of sand, silt, clay, organic matter, air and water, transformed by time, climate, topography, biology, parent material — and us.”
Soil should be alive and teeming with microbes. It’s those infinitesimally small critters that help plants be the best they can be.
“You cannot have healthy, productive plants without a healthy, living soil,” said Steven Zien, a soil expert in Sacramento.
How many microbes? Consider these facts from the U.S. Department of Agriculture’s Natural Resources Conservation Service:
— One cup of soil can hold more bacteria than there are people on Earth.
— A single spadeful of rich garden soil contains more living species than can be found above ground in the entire Amazon rainforest.
— If you packed all the microbes from an acre of land together, they would weigh as much as two cows.
“We know more about things a billion light years away than about what’s happening six inches under our feet,” said Zien, founder of Living Resources Co. in Sacramento, which provides soil and organic gardening consulting.
Microbes play a vital role in soil health.
“Good, healthy soil is alive with beneficial soil organisms known as the soil food web,” Zien said. “These organisms create soil structure, improving drainage and aeration. Nutrients and moisture are stored by the soil biology that makes them available to plant roots, minimizing the need for fertilizer and irrigation. They also provide plant growth hormones and fight off pests, allowing your plants to grow — healthy, pest-resistant and drought-tolerant.”
Organic matter — compost, manure, shredded bark, rice hulls, coconut fiber, peat moss, kelp, bone meal and other natural amendments — does more than keep pH in balance. It feeds those microbes.
“Organic matter is the fuel that makes the whole system work,” said Gisele Schoniger of Kellogg Garden Products in Carson, Calif. “If you do nothing else, put down organic material around your garden.”
Organic matter also helps soil absorb and store water. After storms, some landscapes — especially in areas with clay soil — can get waterlogged.
“The most important thing to do when your soil is wet is nothing,” Zien said. “Walking on or working a wet soil causes compaction, making it difficult for water, fertilizer, air, beneficial soil biology and roots to move through and function in the soil.”
For backyard swamps, Zien has this advice:
“Wait until the soil dries out a little and top-dress with worm castings,” he said. “The soil biology it contains will move into the soil with subsequent rains. These critters will create soil structure that will open up poorly draining clay soils, improving drainage and aeration.
“In spring, when the soil dries out a bit more, aerate the soil. Follow that with an application of an organic fertilizer, more earthworm castings and compost. Avoid tilling your soil — that actually causes soil compaction.”
Those worm castings have an added benefit, Schoniger said. They fight whiteflies and other garden pests.
Sprinkle the castings in a circle around the plant (at the dripline for trees or shrubs), then cover with mulch and let the castings work down into the soil.
Besides being rich in nutrients, worm castings contain a substance that naturally breaks down insect skeletons, she said. But water will bead up on pure castings; they need a little mulch on top to do their garden magic.
“Worm castings are the best value you can get for your garden,” she said. “A whitefly won’t go near a plant that could break its body down.”
Build better soil
Your soil is alive and teeming with microorganisms. Plants need these microbes to break down nutrients.
— Feed the soil, not the plants. Microbes eat organic material such as dead leaves, compost, worm castings and manure. In turn, they process this food into water-soluble nutrients that plants absorb through their roots.
— Microbes need to breathe. To operate efficiently, microbes require tiny pockets of air in soil. If the ground is constantly saturated, they drown. Anaerobic (bad) bacteria, which can survive without air, take over and produce alcohol — and plant roots rot.
— Soil has structure; don’t rip it up. Repeated tilling and churning collapses the soil structure, contributing to the formation of hardpan, an impenetrable layer of clay. By treating soil with tenderness, air pockets are not disturbed. Instead, layer organic material on top; microbes will come up to get it.
— Soil has texture. That texture comes from the mix of gritty sand, smooth silt and sticky clay. Knowing how much of each ingredient is the key to understanding how that soil will perform.
— Test your soil before adding amendments. Know your soil’s pH — its acidity or alkalinity. Inexpensive pH test kits are available at nurseries and home-improvement centers. The lower the number, the more acidic the soil; higher numbers are more alkaline. Most plants prefer “neutral” soil — 6.5 to 7.0 on the pH scale. Acid-loving plants such as camellias and azaleas prefer a pH of 5.0 to 6.0. Never go to extremes on the scale. Other basic soil tests measure macronutrients — nitrogen, phosphate and potassium — that are the primary building blocks for plant growth. More extensive testing will measure secondary nutrients — calcium, magnesium and sulfur — and micronutrients including iron, copper, boron and zinc. These other nutrients act like vitamins for plants, promoting health and strong growth, but too much can be fatal.
— Building good soil takes time. Don’t expect overnight results. When making adjustments, take baby steps.
By Debbie Arrington