How long would it take you to count to a million? How about 100 million? No cheating, counting by ten or one hundred at a time. When we hear huge numbers mentioned, we might think of stars, but for gardeners, we can look closer to home. There are countless numbers of living organisms, little miniature garden workers, right beneath our feet.

Estimates vary because no one could actually count, but the University of Florida Extension postulates that one teaspoon of garden soil can be home to 100 million bacteria and 800 feet of fungal threads. You'll need a scientific calculator to extrapolate that even to just one raised bed. Like stars in the sky, their number is not able to be comprehended by our minds, at least, not mine. But we can improve or detract from their numbers and their activity by the choices we make in our gardening. 

We talked about some functions and physical properties of soil in a previous article here. In it, we discussed that a handful of moon dust could contain all the same parent materials as an Earth soil, but wouldn't make a very good garden. 

All those finely eroded little particles of rock and minerals don't amount to what gardeners call soil until they've become alive. I don't mean the little piece of eroded granite comes to life, but rather that the soil is inundated with living things. To thrive, plants need the living components of the soil: bacteria, fungi, protozoa, worms, and beetles. We call the smallest ones microbes.

A microbe can be a bacterium, protozoan, fungus, or countless other organisms. According to the American Society for Microbiology, the word microbe has two Greek roots: mikros, meaning small, and bios, meaning life. Microbe means small life.

We often talk about improving the structure of our soil by adding soil organic matter (compost) or improving other physical characteristics, like drainage or fertility. But the living component of the soil, the vast and uncountable and for the most part unseen players, are seldom talked about. We can lift a spade full of compost. We can feel the grit of sandy soil in our hands or the smooth and damp texture of clay soil sticking to the pads of our fingers. Most microbes escape our five senses, but that doesn't mean they aren't playing a vital role in the health and performance of your garden.

There's an army of bacteria, fungi, nematodes, actinomycetes (creators of that earthy soil smell), worms, protozoa, and more, all carrying out a dizzying symphony of tasks. Unless you grab a microscope, you won't see most of these organisms, so here's a quick look behind the curtain at what they're doing. 

Fungi

We might envision fungi as mushrooms, and that's correct. But like the apple is the fruit of the much larger and more complex apple tree, so the mushroom is only one small part of the fungus. 

Fungi do lots of important work in our soil. Primarily, they serve as decomposers. Fungi break down dead (and sometimes living) plants, and are especially important for decomposing woody material. In a simplistic view, without fungi, our world would be an unrecognizable tangle of tens of thousands of years' worth of dead trees, shrubs, and forbes. In actuality, it wouldn't exist in its current form at all. 

But fungi also help our plants. While it is true that some are harmful, the majority are not. If you've heard of beans adding nitrogen to the soil, or of the symbiotic relationship of mycorrhizae, that's fungi helping out our garden. Nets of fungal strands called hyphae extend through healthy garden soil, transporting nutrients. When partnered with a plant, these nets greatly amplify the plant's roots' ability to gather needed nutrients and moisture.

Bacteria

There are thousands of species of bacteria in our garden soil. Most of them are unknown or unnamed to science. They're the most numerous of the soil microbe population, with billions (or trillions, or whatever comes after that) in a wheelbarrow full of soil. 

We often view bacteria as a bad thing, or a pathogen, and that is true of some. Many anaerobic bacteria are problem-causing. Gardeners like the aerobic bacteria, which need oxygen. The majority of aerobic bacteria are beneficial, working to cycle nitrogen, decompose dead plant material, and help form aggregates in soil (think chunks of soil instead of individual grains of minerals). They hold nutrients in place as part of their little bodies, which are then available when they themselves die and are decomposed. Bacteria work with plants, providing them with nutrients and being rewarded with sugars exuded from the plant roots. 

Nutrient cycling 

Bacteria break down dead plant material into its component pieces, making it available for plant uptake. They're the reason your compost pile heats up, and the way that coffee grounds or the scraps from your carrots become nutrients again, available for the next crop.

Nitrogen fixation

Some bacteria can actually pull nitrogen out of the air, changing it from the gaseous form, which isn't useful to plants, into other forms, which are, namely, nitrates and nitrites. They also play a role in converting soil nitrogen from one form into another, making it available for plants. Bacteria that fix nitrogen from the atmosphere are in the Rhizobia genus. They are what's in the little packet of inoculant you can buy to treat your bean or pea seeds before planting.

Improving soil structure

Bacteria produce a sticky, glue-like substance called bacterial slime. It sounds gross, but it's great for our soil. Bacterial slime bonds smaller soil particles together into soil aggregates (clumps), which then allow air and water to pass between them. 

If you stacked a bunch of Legos into a huge brick, there wouldn't be much space for air and water. If you form those Legos into shapes like balls, cubes, and footballs, and then jumble them together in a box (or garden bed), there’ll be more available passageways between them for air and water to move.

Nematodes, beetles, and worms, oh my

There are far too many living organisms in our soil to name and describe them all, but here are a few more, some commonly known, others less so.

Worms

Kids love worms. Gardeners love worms. When we dig a spadeful of soil, we can see their tunnels, and sometimes the worms themselves. Hey, I was doing worm stuff here! Worms mix soil, decompose plant material (creating great fertilizer), and leave channels for air and water to percolate.

Protozoa

If bacteria are the chickens, then protozoa are the foxes, eating bacteria and keeping their numbers in check. When the protozoa digest the bacteria, the nutrients stored in the bacteria's body are mineralized and become available to plants again. It's a process that is also done by nematodes. Wait, aren't nematodes bad?

Nematodes

Nematodes are microscopic worms that get a bad reputation for attacking plants and causing disease. But, like bacteria, most are helpful in the garden, acting as predators and decomposers of bacteria and fungi. Some are predators of garden pests like corn rootworms. Others aid in mineralizing nutrients. There are thousands of species of nematodes, many of which live right in our garden soil.

Arthropods

Arthropods include all manner of insects, millipedes, spiders, pill bugs, and more. They shred larger pieces of organic material, making it easier for smaller members of the soil food web to decompose. You've seen this action if you watched an ant carry off a piece of a leaf. Some work underground and some at the soil surface, but their role in a healthy garden is important.

Encouraging Healthy Soil Life

So if soil microbial life is wonderful for our garden, is there anything we can do to encourage it? Do we need to or is it fine on its own? 

Modern human life is designed to eliminate microbes. Our food has chemicals to prevent fungi from beginning the decomposition process. Our kitchens are filled with cleaners designed to kill bacteria. We spray chemicals on our lawns to kill weeds and insects, aiming for a perfect green carpet. And as gardeners, we sometimes do things that aren't in their best interest.

Encouraging our microbial soil crop can be divided into "stop doing this" and "do more of that." But as with all things, a bit of moderation is in order. We're trying to encourage the army of mostly microscopic beings to do their thing, but we don't need to follow a dogma of absolutes. They're pretty willing to multiply and do their thing if we just get out of their way a bit.

Do fewer of these actions

• Rototilling: tilling not only smashes the soil aggregates, resulting in less aeration and drainage over time, but it also breaks up those miles and miles of fungal hyphae so important to the soil food web. 

• Spraying insecticides: remember the arthropods? Insecticides kill insects, but they usually aren't very selective. We need insects for pollination, predation, and their roles in and under the soil.

• Using synthetic fertilizers disrupts the soil food web, which is a finely tuned system. If we provide an easy and quick source of nutrients, it disincentivizes the whole operation. If your job was to shovel manure in return for an ice cream cone, but someone gave you all the free ice cream cones you wanted, would you still want to shovel the manure?

• Leaving bare ground: exposed soil heats up, dries out, and is less hospitable to the microbes in our gardens. As with other lifeforms, if we degrade the habitat, the populations dwindle. 

Practice more of these ideas

• Practice low-till gardening: the violent mixing of soil that occurs with tilling not only breaks up fungal hyphae but also sends surface-dwelling microbes deep, where they can't breathe, brings deeper-loving microbes to the surface, and smashes soil aggregates. If your beds need a bit of loosening, use a garden fork or broadfork to gently break up the soil without causing mass chaos.

• Use IPM (integrated pest management): scouting for pests, mechanical (hand picking) removal, and planting resistant varieties go a long way toward keeping pest and disease problems in check in our gardens. For most garden pest problems, we can use a holistic approach instead of reaching for the chemicals.

• Feed the soil organisms with compost and organic materials: everyone likes to eat. We bring songbirds to the yard by providing food and habitat. The same is true with soil microbes. Compost, mulch, and cover crops provide habitat and food for our soil-dwelling friends. They'll convert it into plant-available nutrients, improve the aeration and drainage of our soil, and help retain nutrients in place. Nice folks, eh?

• Keep the ground covered with mulch, cover crops, or permaculture: A living root system is key to providing food for our microbial friends and sheltering the soil from the effects of erosion, dehydration, and heat. Keep mulch, or better yet, living plants like cover crops on the soil for as much of the year as possible.