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The Soil Food Web

Instead of trying to feed our plants directly, we should trust that they can fend for themselves and start feeding our soil. If nutrients are available in a healthy ecosystem, your plants will find them. As gardeners, it is important to understand our relationship and role within The Soil Food Web.

The Cycle

  1. Plants make sugars through photosynthesis, which are then pushed into the soil through their roots.

  2. Bacteria and fungi cluster around plant roots to eat these sugars.

  3. Protozoa like amoeba then eat these bacteria and fungi.

  4. The waste products from these protozoa are deposited right next to the plant roots (in effect, directly feeding the plant).

  5. Everything living will break down into the soil, releasing nutrients. Insects are the first decomposers to come along. Rolypolies, millipedes, beetles and other insects shred things like fallen leaves and dead animals into smaller parts, making them edible for bacteria and fungi.

  6. Earthworms and protozoa eat bacteria and fungi and their waste products feed plants.

So what happens in our gardens? Why does this cycle often seem to fall apart?

In nature, plants don’t need fertilizers. They are able to control what nutrients they get by controlling the sugars they released. The truth is that inorganic fertilizers dehydrate the soil, kill microorganisms and make plants dependent on this high concentration of nutrients, most of which leech out of the soil. Of course, inorganic fertilizers have their place. They work well for temporary annual baskets and planters, which don't need to be sustainable for an extended period of time. Microorganisms hold nutrients in place, keeping them from washing away or being eroded by the wind. Once this failsafe is removed, fertilizers (which do not include all of the micronutrients plants require) must constantly be applied.

Heavy fertilizing creates plant growth, that’s what it’s for, but because it doesn’t contain micronutrients, the plant cannot properly regulate the amount of nutrients they need.

This causes fleshy, watery growth that stresses the plants out and draws insect pests. Insects love this watery growth, which further weakens the plant, leaving them vulnerable to more attacks. The use of pesticides is not specific to these pests and will also kill predatory species which might ordinarily control pests, now letting them run rampant all over your plants. Plants can also suffer from bad bacteria and fungus.

Good bacteria and fungus make long term associations with plant roots. Once established, they outcompete bad bacteria and fungi. Blasts of inorganic fertilizers kill these protective networks, leaving plants vulnerable to fast growing, harmful species. These bacteria and fungi are opportunists and can only attack plants without beneficial associations. In nature, this gives plants who make these associations with beneficial bacteria and fungi a huge advantage.

Steps towards establishing a healthy ecosystem:

Step 1: Identifying what kinds of plants you have and their needs.

Fast growing, herbaceous plants like annuals and perennials have different needs than slower growers like trees and shrubs. In nature, herbaceous plants will occupy an empty landscape first. These plants germinate easily, have short growing seasons, and are able to reproduce with a small investment of nutrients.

The more permanent a plant is, the more it can benefit from a fungal association, and impermanent plants that grow quickly, but die when the growing season is over, can be better supported by bacteria. These colonies are similar in that they break down dead matter and reproduce quickly. Bacteria and herbaceous plants go hand in hand, impermanent, but essential for establishing a good permanent ecosystem. Trees and shrubs make permanent associations with fungi. This allows for slow and steady food and water year round.

Step 2: The World of Soil

Soil is mostly composed of rock elements and organic elements. Wind and water erosion unlock minerals from rocks in the soil, but the rest come from the breakdown of dead material. Good soil should be only slightly sandy and mostly black and crumbly. Very sandy soil is lacking in organic material. This can be rectified by adding compost as a top dress, or just piling your garden clippings on top of the soil. Soil organisms like earthworms will then pull this material down into the soil, aerating the soil with their tunnels and depositing nutrients near plant roots.

If you have poor soil to begin with, adding organic fertilizers like kelp meal in small amounts will feed starved bacteria and can jumpstart your soil foodweb, getting it back to a sustainable level. Think of your soil in layers: in the forest, trees drop leaves and needles, which break down as they are covered with fresh leaves and needles. Mimicking this in your yard means putting the most accessible nutrients (fully composted materials and organic fertilizers if your soil needs it) closest to the soil so that soil organisms can get to them easily.

Step 3: Compost

There are many products you can buy to feed your soil, but since all of these products occur naturally, with a little more effort, you can produce them yourself. Making your own compost is a great way to get rid of yard waste and food scraps while cheaply producing your own soil.

There are many composting systems, so think about what would work best for you. What kind of waste do you produce? How much and how often? Compostable waste is broken into 2 categories: browns and greens.

Browns are dry, brown things like woodchips, straw, dry leaves, and twigs and are high in carbon. Greens are things like grass clippings, fresh leaves and dead plants, food waste, and manure and are high in nitrogen. Equal parts of green and brown material is ideal for hot and cold composting systems.

Hot compost system

Hot composting is all about providing enough food, water, and air for bacteria to quickly break down yard and food waste into high quality, ready to use compost.

The general idea is a large pile, perfect if you have a lot of yard waste all at once, at least 5”x5”x5”. Once the pile is built, water it thoroughly and cover to keep moisture in. Start out with equal amounts of browns and greens, mixing and layering so that there are equal parts throughout. After 3-7 days, you can turn your pile, taking material off the old pile and rebuilding it right next to where it was. You can then water and cover it again, repeating this until the material has completely broken down.This is labor intensive, but can make a lot of compost within a few weeks or a few months depending on how often you turn it.

The goal is to achieve temperatures of around 170 degrees F. This heat is caused by the movement of bacteria quickly breaking down this waste. Keeping a balance of air and water is essential. There must be enough moisture for bacteria to be able to get around, but not so much that there isn’t enough air for them to breath. The constant turning will help regulate this.

Smell and temperature checks are your best clues as to how your pile is progressing. If your pile smells bad, this could be telling you you are creating an environment for bad bacteria, one that has too many greens or too much moisture and not enough air. This can be rectified by adding more browns and watching how much you are watering.

If you are not achieving high enough temperatures and your pile is not breaking down, you might need more moisture or more greens. Pay attention to what your pile is telling you, the hot composting system is a hands on one.

Cold compost

If you don’t have large amounts of materials or you don’t want to put too much labor into a composting system, you might consider a cold compost system. This is one that you can constantly add to and breaks down very slowly with different bacteria, earthworms, and insects. This pile might take years to turn into compost, but there is no turning involved. Because you do not get the high temperatures you would from a hot compost pile, do not add diseased material, weed seeds, or anything smelly that might draw pests (like food waste). Hot compost can kill most diseases and weed seeds and breaks down fast enough to not draw pests. A cold system is not ideal, as it takes a long time to break down and will not contain as many beneficial bacteria as the hot system, but most gardeners have a pile they can constantly add to and these materials will eventually break down.

Worm bin

If you have a lot of food waste, you might consider a worm bin. Worms process food waste quickly and eliminate disease and odor. This is the most beneficial type of compost as it contains bacteria only found in an earthworm’s gut, which make excellent associations with plants and can prevent a whole host of diseases and pests. A worm bin can be a purchased system or can be as simple as a non toxic box with air and drainage holes. Food waste and paper or wood based bedding and worms are combined in a bin with occasional watering to produce compost faster than a cold system, slower than a hot system, but with the ability to constantly add materials to it.

Additional Compost Tips

Another easy composting method is just to add organic material to your raised beds, flower beds and lawns in the fall when you have put your garden to bed. This feeds the soil over the winter months and keeps present nutrients in the soil from washing away in the rain. This is an easy once a year task that will yield results all spring and summer. The smaller the bits of dead matter, the faster they will break down.

Compost should be kept moist so that bacteria and worms can get to it, which means protecting it with another layer. Wood chips, straw, or woody mulch on top of your compost will keep valuable moisture in and slowly break down to keep feeding your soil ecosystem, nullifying the use of fertilizers for all but the hungriest annuals. Top dressing like this can be done once or twice a year and can save you water and effort. Mulch can prevent weed seeds from germinating, and any that do sprout can be easily pulled from the loose ground and a healthy soil ecosystem will prevent many diseases and pest problems.

Do you have any tips on how you fertilize your garden, or any additional questions to be answered? Let us know in the comments!

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Christine Mellroth
Christine Mellroth
May 09, 2021

Thanks for the soil class 👍

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