117-Compost, Compost Tea and the Soil Food Web, with Dr. Elaine Ingham

| Compost, Podcast

Last week, we “dug” in to the subject of the soil food web with guest Dr. Elaine Ingham. I have long followed and admired Elaine’s work in soil science study, and hearing her describe that it’s actually our plants which are in control of the complex cycle of life beneath the soil surface was fascinating.

If you missed Part One of this two-part conversation, I strongly recommend you begin there. Understanding the relationships between plants and the legion of microbial life within our soil is key to making sense of this second half of the discussion.

Today, we focus on improving the biology in soil through composting, along with how to brew and use compost tea. As we learned last week, making or purchasing compost locally will pack a greater beneficial punch in your garden than applying a product produced hundreds of miles away.

So, how can you take that knowledge to the next level and fine tune your soil food web? Not all compost is created equally. Inputs, timing and temperature can make all the difference.


Dr. Elaine Ingham

Elaine and her team at Soil Food Web Inc. are training a new generation of soil consultants to help meet the need of large agricultural organizations making the shift toward organic soil management. (photo: Courtesy of Soil Food Web Inc.)


Composting Life Back in to Dirt

In Part One of this series, Elaine explained the difference between dirt and soil. Soil is full of life. Dirt, on the other hand, is sterile – lifeless, and that is due to a lack of oxygen and adequate organic matter.

Even when it’s only marginally healthy, soil contains organisms collectively known as the soil food web. It might sound strange, but those organisms – fungi, bacteria, protozoa, micro-arthropods, earthworms, etc. – are just like us in some ways. They require water, oxygen and food for survival. Also like us, they eat, reproduce and die. Blunt, I know, but true.

Healthy soil is teeming with billions of these life forms, each of which play a fundamental role in plant health – and even in our digestive health. As the organisms of the soil food web work, they extract nutrients bound up in soil aggregates. In the process, they build microscopic pathways which aerate soil and improve its ability to retain proper moisture levels.

Those are all very good things, so clearly, we want as many of these microorganisms at work in our soil as possible.

When soil is unhealthy – or lifeless dirt – how do we transform it into a robust soil food web workforce? Well, compost is the best place to start.

Quality compost will feed any active microorganisms already residing in your soil, which will encourage them to multiply. Compost also contains a new population of microbes which make their way into the heap from many sources, including the surfaces of the input materials (food scraps, garden debris, etc.).

Consequently, the species of microorganisms present in the compost will depend on the inputs. The balance of life will also be determined by the compost heap conditions. A booming population of beneficial microbes relies on a good balance of water, food (inputs) and air.


beneficial nematode of the soil food web

Here is a 100x magnified image of a beneficial nematode, which will feed on the fungi and bacteria and excrete the valuable nutrients they hold in a plant-accessible form. (photo: Dr. Elaine Ingham)



Microorganisms must have water in order to perform their decomposition business. This is why the moisture level will impact how quickly a compost heap breaks down. If you opt to take a “hands off” approach and leave things to an occasional rain and the moisture contained within inputs, A small microbial population will eke out an existence, but they will take longer to make their way through the raw materials you add to the heap.


The microbes which gather in a compost heap require some greens (nitrogen) and some browns (carbon) as a food source. Think of it this way: If all you had to eat was potato chips week after week, it would be enough to sustain you, but you wouldn’t be very healthy or very active. If you receive well-balanced meals every day, your energy surges, and you are more productive.

The same is true of microorganisms. When they have a good balance of food, they can work harder and faster to break compost inputs down, while also taking quick breaks to, um, reproduce. These creatures recognize when they have an environment primed to sustain more life, and they respond by multiplying.


Just as in soil, life in compost is critically impacted by oxygen. In Part One of this series, Elaine discussed the effects compaction has on life and nutrients in soil. Compaction squeezes out oxygen particles, creating an anaerobic environment which kills life and causes mineral nutrients to convert to toxic substances, including alcohol.

The same responses occur in a compost heap if it becomes compacted. The varying sizes of the materials you add to the heap create tiny air pockets which allow oxygen to move through the pile. As those materials break down, the natural air pockets are lost, so turning the pile periodically with a pitchfork, for example, is an important step to re-infuse the entire pile with a fresh supply of oxygen.

Just like a good balance of food and water, air keeps microorganisms healthy and actively working to break down materials into finished compost.


Composting operation

Some of Elaine’s clients are composting on a massive scale and require large equipment to aerate the materials and keep the heap aerobic. (photo: Courtesy of Soil Food Web Inc.)


Let It Breathe

How can you tell if your compost heap has become anaerobic? Use your nose.

If your compost heap smells bad – sour, rotten eggs, etc. – it’s telling you it needs oxygen. A healthy decomposing compost heap should always smell earthy and clean. Since the exterior surface of the pile is exposed to the oxygen it needs, you might not notice a problem unless you check for it. Take a moment to dig in, and if the interior has a foul odor, that’s a red flag the pile is suffocating.

Before you see or smell any of these warning signs, the biology within a heap starts to shift. Anaerobic organisms – bacteria – begin to grow. The anaerobic bacteria begin to consume the fungi that you want to promote.

If you come across a white, ashy layer somewhere on the interior of the pile, that’s an indication of a build-up of anaerobic bacteria. It’s your only visible indicator that the compost heap is in danger of going anaerobic

I turn the materials in my compost pile once a week, and in all the years I’ve been composting, I’ve never had a pile turn (or in danger of turning) anaerobic.

Now, I get it – sometimes life gets in the way of even the most well-intentioned composter. So if you see or smell a warning sign that your compost heap is going anaerobic, a thorough mix-up or turn of the material will infuse it with oxygen and get you back in the right direction.

An alternative to turning the materials is to use the handle of a shovel or some other long, round pole to punch holes in various spots through the heap down to the bottom. The holes become chimneys which allow heat within the pile to rise, so cool air can be pulled down into the cavity – aerating the surrounding materials.

Creating good compost, rich in nutrients and beneficial microbes, isn’t hard. It just requires a little bit of attention.


Measuring compost temperature

A compost thermometer is a valuable and inexpensive tool for monitoring the core temperature of a compost heap. Regular temperature readings can really help you understand whether or not you have achieved a good balance of browns, greens, air, and moisture. ( (photo: Courtesy of Soil Food Web Inc.)


The Hot Spot

Have you ever seen steam rising from an active compost pile? That heat isn’t generated by the sun or any other external source. It’s generated by the activity of the microorganisms. They are so furiously consuming and multiplying that they actually put off heat, and once the party really gets going, you can see the heat rise in the cool of the morning. That never ceases to fascinate me.

If you don’t already own one, a compost thermometer is an inexpensive tool to help you gauge the health of your compost. The thermometer has a long probe which, when pushed down into the center of the heap, determines the temperature at the core. Anytime you see reference to compost temperature, it’s the core temperature that matters.

Strive for a temperature of at least 131 degrees Fahrenheit. Pathogens, weed seeds, pest eggs, parasites and other undesirables are unable to survive at that sustained temperature or above.

Microorganisms are more active and reproduce much more quickly at higher temperatures, which is a good thing. During this high level of activity, they consume more oxygen, more water – and more food, which turns raw materials into finished compost more quickly.

While we all want to get our hands on finished compost sooner rather than later, it is possible for a compost heap to become too hot. As temperatures reach around the 170 degrees Fahrenheit mark, so much oxygen is being consumed by the frenetic activity of microorganisms, that the heap is in danger of going anaerobic. So, it’s a good idea to take a few minutes and check the temperature of your compost heap every day during its most active early phase.

Once it’s finished and ready for the garden, compost will be a soil-like consistency and an ambient temperature.

You can choose to work compost into the surface of your garden and landscape, but that’s really an unnecessary step. Microbes already in your soil will join forces with the new team of microbes in the compost to incorporate the amendment into the soil through those microscopic pathways I keep mentioning. You might have been taught to turn it all in, but overworking compost into garden beds breaks up any pathways which already exist.

After you amend, cover the bed with a 2-4” layer of natural mulch. That will protect the surface and the compost from erosion, and it provides another organic food source to promote a healthier soil food web.


Dr. Elaine Ingham with clients

Elaine has been consulting with clients all over the world to convert compacted, anaerobic fields into rich soil. (photo: Courtesy of Soil Food Web Inc.)


Compost Tea

Another method for putting compost to work in the garden is to use finished compost to brew compost tea – a liquid used as a foliar feed.

In Part One, we discussed the microorganisms which live on the above-ground surfaces of plants. One of the many jobs of these creatures is to protect the plant against attack from disease. As a spray, compost tea delivers that beneficial soil biology over the entire surface of the plant.

Microorganisms adhere themselves to each other and to the compost material. So, the first step in creating compost tea is to extract those creatures using water. These tiny organisms are mightier than you might think, so removing them takes more than a good soak or running water. It takes a forceful and precise amount of water pressure to disengage them from the compost materials.

Elaine describes the process of extraction and recommends a cone tank and an air pump to get the job done. The pump is attached at the base of the tank, which is filled with water. Once the pump turns on, it moves the water within the tank. The higher the level of air being pumped into the water, the greater the pressure from the water movement.

The air is pumped into the tank just enough to create the appearance of a soft, rolling boil in the water. According to Elaine, that’s an indication that the pressure of water moving around in the tank has reached around 80 psi – the point at which the organisms are pulled from the compost material.

A small bag of compost is placed into the tank right in line with where the air bubbles are moving up from the valve of the pump.

This process doesn’t take long. In fact if the correct pressure is maintained, about 75% of the organisms living in the compost are extracted within 15 minutes. Compost containing a good population of fungi will turn the water a deep brown color. However, water which turns yellow or a honey-like shade contains mostly bacteria.


Dr. Elaine Ingham making compost extract

Here, Elaine is filling a mesh bag with compost to prepare it for the extract process. The cone tank behind her on the left is connected to an air compressor to move water at sufficient pressure to force the microorganisms bound in the compost to release into the water. (photo: Courtesy of Soil Food Web Inc.)


As we learned in Part One, a higher ratio of bacteria in soil is ideal for promoting weeds. We want a higher fungal count for our garden to benefit our desired ornamental and edible plants most.

Once the organisms have been extracted, they should be allowed to multiply in the extract. Feeding encourages reproduction. So, where does the food source come from? Food products are available for purchase which, when added to the water at the start of the extract-making process, will feed and promote multiplication of specific types of organisms after extraction.

Is your goal to increase fungi or protozoa? There’s a food designed for many of the microbes within the soil food web, which means the biology in compost tea can be customized.

When kept at a temperature of 70 degrees Fahrenheit or warmer, the organisms will be active and ready for garden application within 24 hours. Microorganisms are less active in cooler temperatures, so extract stored at cooler temperatures, requires up to 48 hours for the population to expand to the point that the tea is ready to apply in the garden.

One organism population which cannot be grown is the nematode. These creatures will be present in compost and compost tea, however beneficial nematodes reproduce more slowly than their microscopic neighbors. Their population will increase over time in your garden, but they won’t multiply in compost tea.


Soil fungus under a microscope

The world under a microscope is pretty fascinating for kids of any age. Check out the structured segments of this soil fungus at 400x magnification. (photo: Dr. Elaine Ingham)


Where the Magic Happens

Finished tea sprayed on plants, delivers the soil food web cycle right to foliage. Just like under the soil surface, the fungi and bacteria in tea are loaded with nutrients from their time spent feeding on organic materials. As the protozoa and other microbial predators feed on the bacteria and fungi, the excess nutrients are excreted in a form that plants can take up through stomates.

Stomates on leaf surfaces open and close based on the concentration of CO2 in the surrounding atmosphere. Like humans, the microorganisms of the soil food web consume oxygen and expel CO2. So when you spray them onto foliage in compost tea, they increase the level of CO2 near the foliar stomates and the stomates open to take in the nutrients the microorganisms make available.

I don’t know about you, but I think that is pretty amazing. All of this magic is happening in our gardens every day. We just need to be more aware of it and learn how to give way to these remarkable cycles of nature.


Compost tea application

Compost tea can be applied by a humble pump sprayer in the home garden or using heavy equipment sprayers as seen here on a seed potato crop in Montana. It is also disbursed by air, using planes and helicopters. (photo: Courtesy of Soil Food Web Inc.)


Keeping It Local

Okay – maybe you aren’t able to make your own compost due to space restrictions or HOA covenants. Maybe you make the compost, but you just don’t have the time (or the inclination) to make compost tea. Purchased products are widely available, but as I always say, quality is key.

If you purchase compost, look for certified compost, so you can feel good about the quality. Also, look for local compost, since it will contain more of the microorganisms needed by plants in the mineral makeup of your area’s soil.

Many nurseries and garden centers also offer compost tea for sale, but as with all things, buyer beware. Some companies brew tea for several days before they contain it to grow the microorganisms. During that extended brewing period, the microbes become inactive. Within a few days of brewing, microorganisms stop multiplying and actually fall asleep, which means they won’t be alert to glue themselves to the surface of your plants when sprayed.

That matters, because if they don’t adhere themselves to your plant, most of the population rolls off to the ground.

How do you know if the compost tea at your local nursery is worth buying? You could check the color. Again, it should be a dark brown to indicate that it contains plenty of fungi, but that’s no guarantee it’s worthwhile. The best way to judge the quality of compost tea is to bring a little home and look at it under a microscope.

You do own a microscope, right? No? Well, this might just inspire you to add one to your must-have list.

Through the power of magnification, you can determine if you have a higher level of bacteria or fungi, whether or not you’ve got some predatory microbes at work, and how active all those creatures are.

A microscope could not only show you the quality of compost tea you are considering but, also, reveal the biology in your soil and compost. Gathering this information may take a little time and effort, but if you have kids or grandkids, this activity will be a hit. Together, you can actually watch as the predator organisms eat the bacteria and fungi, which is pretty cool for kids of all ages.

Plus, knowing which aspects of your soil food web need fine tuning will give you a leg up in arming your plants to feed themselves through this natural cycle and be better equipped to fend off pests and diseases.

Once your soil food web is robust, your garden problems and maintenance will go down, and your plants will be healthier than ever.


organisms of the soil food web

You can determine just how active your compost tea is by viewing it under a microscope. Under the magnification, you can observe their movement and even watch as larger organisms feed on the bacteria and fungi. (photo: Billy Schlee)


The Devil Is In the Details

The subject of compost tea has always been a little controversial. There are some soil scientists who feel it’s useless or even harmful. I asked Elaine for her take on why opinions vary so widely. It’s her observation that it comes down to using quality materials and the right technique and timing.

For example, compost tea will contain pathogens if it is made from compost which didn’t reach temperatures hot enough to kill them. Spray those pathogens onto your plants, and voila, you’ve got problems. Tea made from composted manure could cause serious harm if the manure contained harmful pathogens. Manure from animals given feed treated with antibiotics will carry those antibiotics forward into the tea, and that will kill soil biology.

How the compost and tea are made will effect the impact – good or bad – an application of compost tea will have on your plants.

Is it necessary to use compost tea for a healthy garden? Not necessarily. Elaine suggests that it is worthwhile in the first season or two of converting poor soil (or dirt) into a healthy growing medium. Compost tea will cover the foliage of your plants with good biology which can reduce or eliminate the need for you to treat for disease.

A foliar application of compost tea won’t be necessary, once your soil food web is established and humming along with yearly or twice-yearly amendments of compost and a layer of natural mulch. There will be enough microbial life that the beneficial insects in your landscape will spread it on to plants for you.

So, has this two-part dive into the mind-boggling world of the soil food web whet your appetite for more? Elaine’s online courses or consultation training program might be of interest to you. She and her team at Soil Food Web Inc. are working with more and more large-scale agricultural operations all over the world and are in need of a new team of soil science consultants to help these operations convert from toxic chemical-based agriculture into a biological agricultural approach.


GEOTEA compost tea brewer

GEOTEA machines are designed to make compost tea on a large scale. You can see the rolling “boil” on the water surface and the dark brown color indicating that the compost used for this tea has a good fungal population. (photo: Courtesy of Soil Food Web Inc.)


You may have some follow-up questions for Elaine. Well, I’ve got good news. I plan to invite her back for a Q&A session to answer the questions that audience members are sharing in response to this series. Submit your question in the Comments section below (or in Part One), and I’ll be sure to include it in my follow-up podcast.

Last but not least if you haven’t listened to the recording of this podcast, I hope you will scroll to the top of this page and click the Play icon in the green bar under the page title. Hearing my dialogue with Elaine will help to reinforce the wealth of information that came out of our conversation.

Links & Resources

Episode 016: Composting Guide A to Z: The Quick and Dirty on Everything Compost

Episode 116: Understanding the Soil Food Web, with Dr. Elaine Ingham

joegardener Online Academy: Master Pests, Diseases and Weeds – my newest online course! Just $47 for lifetime access.

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About Joe Lamp'l

Joe Lamp’l is the creator and “joe” behind joe gardener®. His lifetime passion and devotion to all things horticulture has led him to a long-time career as one of the country’s most recognized and trusted personalities in organic gardening and sustainability. That is most evident in his role as host and creator of Emmy Award-winning Growing a Greener World®, a national green-living lifestyle series on PBS currently broadcasting in its tenth season. When he’s not working in his large, raised bed vegetable garden, he’s likely planting or digging something up, or spending time with his family on their organic farm just north of Atlanta, GA.

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