Soil Food Web: What Bacteria, Fungi and Protozoa Do

Soil is a food chain, and most growers never see it. Bacteria and fungi break down organic matter and hold nutrients in their bodies. Protozoa and nematodes eat them and release part of what they ate where roots can reach it. Plants keep the whole thing running by leaking sugars from their roots. Here's who lives down there, what each group does, and what to do when your soil has gone quiet.

Who lives in healthy soil

"Soil food web" is shorthand for who eats whom underground. Four groups do most of the work.

Bacteria. The most numerous group. They decompose simple organic compounds, and some can convert nitrogen gas from the air into forms plants can take up.
Fungi. They break down tougher material such as woody matter and stems. Many form threads (hyphae) that spread through the soil and help bind particles into clumps.
Protozoa. Single-celled grazers. They eat bacteria and release nutrients as waste.
Nematodes. Microscopic worms. Many feed on bacteria or fungi; a few feed on roots. In a balanced soil the helpful ones outnumber the harmful ones, but we make no claim that any product controls the harmful ones.

Mycorrhizae are a special case of fungi. They attach to roots and trade nutrients and water for sugars from the plant. That's a different partnership from free-living bacteria, and the two aren't interchangeable. We make no mycorrhizal claim for Microbes, so don't buy it for that purpose.

What each group does for your plants

Bacteria decompose organic matter, some fix nitrogen, and some help release tied-up phosphorus. The result is nutrients moving from "in the soil" to "available to roots." Fungi break down tougher material and build soil structure with their hyphae, which gives you crumbly soil that holds air and water. Protozoa graze bacteria and release nutrients, so the supply stays steady near roots. Nematodes graze bacteria and fungi and move nutrients along, which is the same cycling one step further up the chain.

Nutrient cycling is why any of this matters. A bacterium holds nitrogen in its cells. When a protozoan eats it, the protozoan takes what it needs and excretes the rest as plant-available nitrogen, right where roots are. Without grazers, much of that nitrogen stays locked up in living cells.

Our product documentation describes the functions Microbes is meant to support in your soil: decomposing organic matter, solubilizing phosphorus, fixing nitrogen, releasing chelating compounds that help move minerals like iron and zinc, and improving soil structure and water retention. Those are general soil-biology functions. Results depend on your soil, temperature and moisture.

What damages soil life

Sterile or heavily processed mix. Bagged potting mix often starts with very little living biology.
Drying out and waterlogging. Most soil organisms need moisture and air together. Long dry spells and soggy, airless soil both hurt them.
Heat. Soil in a black pot in direct summer sun can get hot enough to stress organisms. Mulch and shade help.
Tillage and compaction. Digging breaks up fungal networks, and compaction squeezes out air.
Bare soil. With no plants and no mulch, there's nothing feeding the system.

Most of that list is a fixable habit, not a mystery. Mulching and watering well cover several items at once, and our mulching guide goes deeper on the outdoor side.

Why does my potting mix feel dead?

If your mix is light, dusty, smells of nothing, dries hard and sheds water, or stays wet and sour, the biology is probably thin. Healthy soil usually holds together in a loose clump, has an earthy smell and takes up water evenly.

We can't diagnose your soil from a description. A cheap check: squeeze moist soil in your hand. It should hold a shape and break apart with a light touch. If it does neither, look at structure, watering and food before blaming the organisms.

What to do

Start immediately. Don't wait for a new bed, pot or mulch layer to "settle" first. Microbes feed soil biology, which is what breaks organic matter down, so waiting delays that process.
Add Microbes first in the mix. Our order is water, then Microbes, then Veg or Bloom powder.
Dose from the feeding guide. Microbes is dosed at 1 to 3 ml per gallon of water (about 1/4 to 3/4 tsp), applied as a drench at the base of the plant.
Always apply it with a microbe food. Our product documentation says to use Microbes together with one of Veg, Bloom, King Krustacean or Phishy. Pair it with a food so soil life has something to work on.
Keep soil damp, not soaked. Organisms need water and air.
Mulch outdoors. It shades the surface and feeds the system as it breaks down.
Store the bottle below 100 F, out of direct sun.

How fast do microbes work?

We don't publish a timeline, and a firm number would be a guess. In general, biological activity speeds up with warmth, moisture and available food, and slows when soil is cold, dry or waterlogged. Plant changes you can see usually lag the biology by a while, so judge new growth over a few weeks rather than a few days.

Where Growganica fits

Microbes is the first step of our program. The label descriptor is "full spectrum compost tea," and it's derived from vermicompost, fish protein hydrolysate, soy protein hydrolysate and seaweed. The guaranteed analysis is 0.01-0-0, so it isn't a nitrogen fertilizer. It's there for the biology. It comes in 16 fl oz and 32 fl oz sizes. At the top dose of 3 ml per gallon, a 16 fl oz bottle treats about 157 gallons.

Two honest limits. The label makes no microbial content claim, and we don't claim Microbes controls plant diseases.

Veg and Bloom are built as low-nitrogen formulas that rely on soil biology to supply the rest, so they should be used with Microbes or an already living soil. For houseplants, the same Microbes dosing applies. The feeding schedule lays out the full routine.

Want the bigger picture on why we build around biology? Read How to Use Soil Microbes Organically for the broader case. This guide is the how-it-works version.

Frequently Asked Questions

What do soil microbes actually do?

They move nutrients. Bacteria and fungi break down organic matter and hold nutrients in their bodies. Protozoa and nematodes eat them and release part of what they ate in a form roots can use. Some bacteria also convert nitrogen gas from the air into forms plants can take up, and some help release phosphorus that is tied up in the soil. Results depend on your soil, temperature and moisture.

Why does my potting mix feel dead?

Bagged mix often starts with very little living biology. If yours is light, dusty, smells of nothing, dries hard and sheds water, or stays wet and sour, the biology is probably thin. We can't diagnose your soil from a description, so squeeze a handful of moist mix. It should hold a shape and break apart with a light touch. If it does neither, look at structure, watering and food before blaming the organisms.

How fast do microbes work?

We don't publish a timeline, and a firm number would be a guess. Biological activity speeds up with warmth, moisture and available food, and slows when soil is cold, dry or waterlogged. Plant changes you can see usually lag the biology, so judge new growth over a few weeks rather than a few days.