Compost: a loosey-goosey term

Jan 29, 2022

I have an unpopular opinion I want to share with you today: most compost is not it’s all cracked up to be.

Maybe a more positive spin is to say, we’re not meeting our potential at large when it comes to compost.

And why would we be? Afterall, the word “compost” is defined as organic material that’s been decomposed – 😶 a definition that begs more questions than answers

What type of organic material - food waste, yard trimmings, manure?
How was it decomposed – was it fed to worms, rotted in a static pile, left to ferment in a tight bucket, strategically heated and turned?

By this definition, depending on the type of organic material and how it was decomposed, “compost” could possess the power to restore health to an ecosystem or… wreak havoc on it. Yikes! Is it time we find different terminology to more accurately describe products in the “compost” category? I’d say so! Your suggestions are welcome in the comments.

My intention for these next couple articles is to explore what compost even is (this post), and put into perspective where we’re at in the history of compost making (next post). I’m mostly thinking from the perspective of the ever-popular commercial method of thermophillic composting, and I haven’t even gotten around to writing about liquid compost! There’s so much to consider here, so don’t be shy, please send me your own thoughts and queries related to organic amendments via comment or email. I LOVE hearing from you.

#CompostGoals

What would you say is the purpose of adding compost to our soil systems?

I suspect many people would say, to serve as organic fertilizer or nutrients, and leave it at that, but compost can be so much more. Here’s what I want out of compost…

Waste Diversion – a blessing & a curse

I worked in a garden center once. When a customer would come in interested in backyard composting the first question I’d ask them was…

What’s your primary goal: do you want to divert food and yard waste from the landfill or create a rich amendment for your garden?

There’s no wrong answer, either motivation seems honorable to me, but it is important to know because as it turns out those can be two very different goals, requiring different approaches.

Those only interested in diverting waste were sent home with a simple set-it-and-forget-it method that I would consider “static composting”, along with tips on how to avoid pests. The gardeners on the other hand were sent home with brochures and helpful websites to understand carbon to nitrogen ratios, temperature, aeration, and moisture.

If managed appropriately, it’s likely the static compost method would yield a great garden amendment in time, but for those interested in making amendments in only a matter of weeks or months, the inputs must be managed more… thoughtfully.

This concept of a motive driving the methods and outcomes of a composting process applies to industrial compost producers as well. Depending on their intention, consumers will end up with a very different product.

Many industrial compost makers today primarily serve as waste diversion facilities. Meaning, they fulfill a need in the landscaping and food market as a receptacle for waste, effectively diverting it from a landfill. This is a great thing! To put it simply, large drop-offs of landscaping and/or food waste are ground up and heaps of it are managed according to regulations meant to ensure the safety of the end product i.e. avoiding contamination from heavy metals and human pathogens. There are often little to no quality control measures to ensure the material is beneficial to plants and soil systems. In the end, they typically end up with a material that is rich in organic matter (OM), but lacking in soil life.

There’s a lot of things going right here, we’re diverting that waste y’all and we’re makin’ sure we’re being safe about it, but might I point out the MISSED OPPORTUNITY! All of that waste comes in with a diversity of organisms living on the surfaces of leaves, branches, food scraps and unfortunately, much of it DIES because of how the material is managed.

No one seems to be knowingly destroying the biodiversity of their compost. In fact, most people don’t know to be concerned with that in the first place. Imagine, what might our landscapes, gardens, and fields look like if we were just as informed and focused on the biological possibilities of compost as we are about its waste diversion benefits?

Compost Biology Basics Deep-Dive

Below are my top 2 concerns when it comes to the biology of conventional compost.

1. Bacterial Blooms – the problem with bacterial tyranny

Just like in tilling, the grinding up of all that organic matter (OM) and frequent turning of compost piles really disturbs larger organisms (like fungi, nematodes, arthropods, etc.). As those organisms die off with each disturbance, bacteria happily decompose their remains and have free reign to proliferate due to nobody bein’ around to prey upon them. If the piles aren’t intentionally given food sources, environmental conditions, and protection necessary for other organisms to thrive, then we end up with a compost that’s got a lot of bacteria and little else.

Why does that matter?

When you consider how bacteria-dominance is one of the very issues we’re trying to correct through restoration efforts, (like y’know compost application itself…) it makes you wonder if adding more bacteria-rich material is really helping anyone. On the one hand, the organic matter could serve as food and habitat for any larger organisms that do happen to be present in the soil where it is applied. But bacteria-dominant compost certainly isn’t doing any favors for 90% of plant species that rely on fungi (… basically everything but weeds), nor does it significantly help a soil system along in its process of building structure (seeing as a diversity of interacting organisms are key to aggregate formation i.e. soil structure).

2. Anaerobic Activity – the scoop on low-oxygen conditions

You’ve probably heard one trait of unfinished compost to be heat. Let’s talk about that…

Why does compost get hot in the first place?

When a microbe reproduces it releases some heat. At approximately 1 millionth of a degree per bacterium it’s not a lot of heat, but when you multiply that by BiLLiOnS of organisms in a small space, we’re talkin’ lots of degrees - like 10 degrees every 20 minutes! So, because compost is filled with yummy microbial foods, they reproduce like crazy and the piles heat up.

This heat byproduct is a useful thing because human pathogens and most plant pathogens cannot tolerate these high temperatures (how convenient!), making the heat an effective way to kill off harmful microbes and seeds. But we have to be thoughtful in how we leverage this natural process.

For instance, in nature, what happens if a group of organisms over-reproduces?

Just think of deer populations for a second… when they reach too high a number their food sources may dwindle due to over foraging, which can ultimately result in starving deer, not to mention have effects on other species that rely on that same vegetation, oof!

In the case of compost, the resource that’s typically lost first is oxygen (beneficial organisms that we want in our soils are aerobic, meaning they take in oxygen just like you and me). If their populations get to the point where they’re consuming all of the oxygen available to them in their environment, then other microbes will stir awake and gladly take over in the anaerobic conditions. Decomposition is still happening, which might I point out, aligns with the current definition of compost, but the problem is anaerobic bacteria produce alcohols as a byproduct of their metabolism and these compounds are i) harmful to plants and ii) combustible at ~180 degrees F!

So, for these reasons, a properly managed thermophilic compost pile is strategically turned at certain intervals to keep oxygen in the pile* and it is only finished when the pile cools and plateaus in temperature. This indicates aerobic bacteria have consumed almost all of the readily available food and the microbial populations at large are able to stabilize.

*note the conundrum of needing to turn the pile to keep appropriate oxygen levels, and yet turning is disturbance that can lend itself to bacterial blooms. What to do about this? We can talk in the comments!

Concluding Thoughts

I don’t mean to make our heads spin, so quick check-in: WHY are we thinking through all of this?

When you consider that at best, poorly managed compost could be harboring harmful microbes (i.e. your next food poisoning or your plants next root-rot), or at worst it may act as an herbicide, or even worse it could spontaneously combust… you start realizing it might be time we stop assuming all “compost” is “black gold”.

Understanding what unfinished compost and high-quality compost are really all about on a microbial level is the only way to know if it’s actually helping us achieve our goals.

I’m not saying all conventional compost is garbage; I’m saying no compost is created equal and we stewards ought to be mindful of that as we aim to truly restore landscapes and nurture plants.

May we use discretion before calling something rich compost and using it on our land.

The exciting news is, we’re at a point in compost history where we can ask formerly impossible-to-answer questions about these amendments, whether we’re making or buying them. We can actually understand where the wisdom and missed opportunities are in the conventional way of doing things and find ways to improve.