Learn about the basics of healthy soil growth, and how to add nutrients to soil to promote healthy microorganisms, bacteria, and fungi growth while promoting worm activity.
Soil. Dirt. Earth. It seems like pretty simple stuff. We stick a seed in the ground, and up pops a zinnia or a pumpkin. We dig a hole to plant a tree or a bigger hole to pour a foundation for a house. Sometimes, earth moves (unfortunately), but mostly, it just sits there, doing nothing. Why talk about it?
If you ask a small child what soil is, you might be told it’s dirt. Ask an 8th-grade student after their earth science class, and they’ll tell you it’s weathered pieces of bedrock broken down by erosion into smaller and smaller particles. A high-school student will have forgotten about it, and a farmer will tell you land is valued by the fertility of its soil. A farm with “good” soil sells for more than one with poor soil. Gardeners, the strangest of the bunch, pick up handfuls of soil and smell it, inhaling deeply and smiling.
Soil is more than all of these definitions, and more than a collection of weathered minerals, little pieces of granite, mica, and quartz jumbled together. It’s a structured, layered composite of minerals, decayed and undecayed organic matter, air, water, and an entire community of living organisms — billions of them in a handful.
More Than Worms
Gardeners tend to get giddy when they turn over a spade of soil and see earthworms. If you ask most gardeners, no worms are bad, and many worms are good. They’re right. Earthworms eat dead plant matter, and their excretions, also known as “worm castings” or “vermicompost,” make excellent homegrown fertilizer that’s pretty expensive to buy. Earthworms help mix organic matter deeper into the soil and improve water and air infiltration rates. So, earthworms are a good sign, but many other soil organisms are doing the same work and more.
More microorganisms exist in a few tablespoons of healthy soil than there are people on the planet. We can see a few: earthworms, grubs, centipedes, and beetles. Most we can’t see, though: bacteria, fungi, protozoa, nematodes, and more. This smorgasbord of life in the soil beneath our feet is the magic of how plants grow.
All the living things in the soil and the plants they interact with comprise the soil food web. What makes the soil food web so important is the interaction between microbes and plant roots in the rhizosphere. Bacterial mineralization, the process of bacteria breaking down organic matter to make it available to plants, of nitrogen is cool, but it’s a whole lot cooler if it happens right next to our plants’ roots.
Bacteria Everywhere
Your parents may have admonished you to wash your hands after you came in from playing in the yard. There could be germs! They were right.
Billions of bacteria live in the soil — and that’s a good thing. While we often think of bacteria as something to be avoided, they’re a force multiplier in the soil. Bacteria break down plant material, fix nitrogen from the atmosphere, hold nutrients in their bodies for later use, and even bring nutrients to plant roots in exchange for tasty plant exudates. Gardeners and farmers are interested in fostering aerobic bacteria (bacteria that need oxygen).
Compost is excellent for plants, but your zucchini’s roots can’t snag nitrogen directly from a dead tomato vine. The vine’s cellular wall is made of cellulose, pectin, proteins, enzymes, and other materials. How can the zucchini get the nitrogen out of the protein molecule and into a form it can use?
As it turns out, the compost pile is really a recycling site. Decomposers are hard at work eating and then excreting, turning that pile of garden waste, lawn clippings, and kitchen scraps into humus, tiny bits of organic material, and plant-available minerals. Bacteria in the soil or in the compost pile eat and digest those tiny particles of organic matter, breaking them down into plant-usable forms of nutrients. The bacteria release some nutrients to be taken up by the plant roots and incorporate other nutrients into their bodies to be released when they, in turn, are eaten.
Bacteria do more for the soil than break down organic matter and fix nitrogen, though. They also make bacterial slime for their own benefit, but with the added plus of sticking small soil particles together to form aggregates. So not only are bacteria feeding the plants, but they’re also improving soil structure. Not bad for “germs.”
Fundamental Fungi
No dad jokes about being a fun guy here. Fungi are important decomposers and symbiotic partners for our plants, and they reside in the soil. We’re most familiar with the fruiting bodies of fungi, which we call “mushrooms” and happily dine on. However, the real work is done by the filaments extending for miles throughout the soil under the surface.
The fundamental fungi building blocks are hyphae, composed of one-cell-wide strands. Hyphae can pass water and nutrients from one cell to the next. Hyphae form networks of threads called “mycelium.” These networks can be enormous, covering acres or even square miles underground. When mycelium forms a partnership with plant roots, it’s called a “mycorrhizal network.” That’s the good stuff.
Mycorrhizal networks benefit both the plant and the fungi. The plant exudes carbohydrates from its roots, which the fungi feed on, while the fungi uses its vast system of hyphae to bring water and nutrients to the plant roots. Since the mycelium is much more extensive than the plant’s roots, the plant’s reach is vastly improved. Visualize it like this: Instead of looking for a new job by yourself, you have 10,000 friends also helping you look, each with their own network of contacts and potential employers. Your “reach” is greatly extended.
Other Soil Inhabitants
- Protozoa. Protozoa are single-celled microorganisms that keep the number of bacteria in check and serve as food for larger soil organisms. While eating thousands of bacteria, the protozoa digest and excrete them, mineralizing the bacteria and those stored nutrients into plant-available carbon and nitrogen.
- Nematodes. Similar to protozoa, nematodes also mineralize nutrients found in bacteria. They’re microscopic worms (roundworms) with a bad rap for causing disease and attacking plants. However, only a fraction of nematodes, which number up to a million species, are harmful. The majority are predators and decomposers of bacteria and fungi.
- Insects. Insects with shredding mouthpieces (shredders) impact the soil food web. They go about their day tearing up organic matter and, in the process, make it easier for bacteria and other decomposers to do their work. Two important arthropods are mites and springtails. More commonly and easily seen examples are termites and ants.
How to Add Nutrients to Soil
Knowing how to spell “mycorrhizal” might win you a spelling bee, but what else can you do with this information? The complexities of the soil food web are limitless, but we don’t have to understand it all (and we probably never will) to benefit from and encourage it.
First, if you have an established garden, never let your rototiller in it again. While tillage can help create a new garden from hard-packed sod, after the first season, you’ll be doing more harm than good. Tilling destroys miles of fungal networks, smashing soil aggregates, collapsing pore space and channels, and chopping up your earthworms! (Earthworms don’t often regenerate from the pieces. Usually, they die.)
Second, keep adding organic matter. Soil organic matter is what feeds your soil life. Adding compost is one way, but mulching, using cover crops, and leaving plant roots from dead crops in the ground are others. Rarely is bare soil seen in nature. Instead of keeping the aisles clean, mulch them. Chop and drop in the autumn instead of removing plants. As Diane Miessler says in her excellent book Grow Your Soil!, “In effect, healthy soil is an ongoing composting process.”
Healthy soil life will astound you with the lush green results aboveground. Leave the blue fertilizer powder at the store, and encourage the symbiotic relationships of plants and fungi. And relax. It’ll be okay. Nature was growing plants successfully long before humans ever thought of sowing them in rows.
Andy Wilcox is a freelance writer and flower farmer who’s passionate about gardening, horticulture, and forestry, and who believes healthy soil leads to healthy people. He can be reached at Andy@ThatGardenWriterGuy.com.