Not all compost is created equal

By Coach Mark Smallwood
Originally appeared at

Just as the statement “milk is milk” is patently not true, so is the idea that all compost is created equal. Dictionaries and encyclopedias simply define compost as “rotted organic matter made from decomposed plant material.” And while piling plant material in a heap and waiting long enough might result in rotted organic matter, it would still be a far cry from the truly fertile whole-food nutrition on which plants will thrive. Whether gardeners and farmers make compost themselves or get it from an outside source, there is a wide range of practices that can lead to the final compost product. What matters in the end, though, is whether it will help your plants flourish—or might it actually hinder the growth of your garden?

Simple recipes usually result in a mildly fertile and generally decent compost that gardeners can make without too much effort or background knowledge, a kind of Compost 101. But for master gardeners or farmers whose livelihoods depend on producing the best crop they can, there are few “best practices” resources out there for tried-and-tested master-level compost production. From community and commercial composting facilities to farmers and gardeners nationwide, what you most often see is the Compost 101 recipe on a variety of scales.

Here at Rodale Institute we’ve been making compost for decades. We already know that compost improves soil structure and can increase the water-holding capacity of soil—meaning even when there is a shortage of rain, gardeners and farmers have a better chance of still growing a good crop. Compost can also keep the soil pH in balance without additional amendments.

But it wasn’t until recently that we started to look a little more closely at our compost. We actually began to take a look at our compost under the microscope and discovered that not even all of our compost was created equal.

What breaks down organic materials into compost and creates a nutritious support system for plants is the microbiology living in the compost—the living, breathing, eating, and expelling organisms. Bacteria, fungi, protozoa, nematodes, and microarthropods all have a part to play in making top-quality compost. And all of these creatures need to collaborate in the right balance. It’s not just a matter of who’s in your compost, but how big their families are. Different plants require different amounts of each type of microorganism. For example, weeds like to grow in soil or compost with lots of bacteria. Woodland plants require more fungi.

So the next generation of compost questions we are trying to answer are about digging in a little deeper, improving upon the solid base of general information we already have about compost and making the potential benefits of compost more of a sure thing. What does soil disturbance or compaction do to the balance of microorganisms? How do cover crops select for particular microbial communities? Can we reduce or even eliminate weeds by tweaking the types of critters in our compost?

We’re looking at the compost recipe all farmers must follow to be USDA certified organic and identifying how to improve the process. Basing the recipe on temperature rather than a prescribed number of turns means following the biological processes of the microorganisms—turning and aerating the compost piles when it is beneficial to them and not detrimental.

Taking the idea a step further, if we can manipulate the microbiology of the compost so it is ideal for a specific crop plant, we should be able to build a compost recipe matrix that coordinates with what you want to grow. This is really Compost 401. It’s time to figure out how to make compost live up to its potential every time. A lot of people make compost. The question is: What’s really in it?

Next post, I’m going to talk about how these microbes in compost and soil make nutrients available to plants, aka nutrient cycling, aka “cake and cookies.” Stay tuned.

Coach Mark Smallwood has been dedicated to environmental sustainability, efficiency, and conservation for decades. Since joining Rodale Institute in December 2010, he has brought heritage livestock back to the institute’s 333-acre farm, expanded and enhanced its research efforts, and launched Your 2 Cents, a national campaign to support and promote new organic farmers. In recognition for his sustainability efforts, Coach was chosen as a messenger for Al Gore’s Climate Project, presenting to more than 15,000 people on the effects of global warming. Last, but certainly not least, as a longtime organic farmer and biodynamic gardener, Coach has raised chickens, goats, sheep, and pigs, and driven a team of oxen.

11 Responses to “Not all compost is created equal”

  1. Eugenio Bayancela

    This approach is very interesting, it is necessary to monitor microbiological populations Are you also consider the group actinomycetes?.

    Thank you,

    Eugenio Bayancela, agr

    Montréal, Qc – Canada.

  2. James

    Glad to see you are researching further. There is a vast range of conditions in making compost – studied composting as a nutrient return to the soils including historic uses to modern, methodologies, materials, applications and soils it was/is being applied globally and yes not all compost is equal. You will find besides the microbial populations differences, the culture of the user is also a factor in how compost is made and used and from what which changes the chemical make-up from one compost pile to another. I have been using mostly earth worms as my ‘composters’ for creating the nutrient returns for my garden, I have used other methods but find earth worm munched compost to be the best nutrient return; fiber content and active ‘breaking down’ within the soil is another area of interest where you may want to look at the microbial populations changes – note we know only about ten percent of what takes place in the soil, which scares me to some degree, the soil is after all the real ‘lungs’ of the earth – soil is defined as particulate suspended in atmosphere (created by microbial activity).

  3. Peter Crownfield

    I’m glad to see these efforts to develop more detailed and specific knowledge.

    At the same time, I wonder if tailoring compost to a specific crop won’t tend to reinforce the destructive practice of monoculture by making the soil better for one crop and less suitable for others.

  4. Robert Erickson

    This is an intriguing concept that I have been curious about. Different input have got to result in variable outputs. My question is, just how wide a variance have you found? Is it potentially controllable by a small scale home composter or is it primarily for a large scale operation?

  5. Shankarananda das-Hilo, Hawaii, Big Island, Puna District -Kalapana

    Aloha Mark, thank you for doing all kinds of research for the benefit of humanity and mother earth. I read that every civilization that destroyed their soil, also collapsed! Moral: If you don’t take loving care of Mother Earth (“Bhumi” in the ancient Sanskrit Vedas), she will not take care of you. It’s a symbiotic/loving/caring relationship.
    1- Another angle towards composting is the types, quantities and proportions of ingredients put into the pile. and
    2- what about adding in EM other micro organisms on the market?
    3- burn wood/cardboard, sawdust, brush/branches, on top of the compost pile to add postash? when we plant trees, we make a fire in and around the hole, then add compost/manures in the planting hole
    4- to control bad nematodes, we sprinkle sawdust, dried grass clipping a foot or two around the trunk of the tree and burn with a propane weed torch, and turn it into ashes
    5- mix red hot chili peppers with peppermint, and spray around the roots of trees for nematodes.
    we have many more ideas we can discuss, be nice if someone would do methological experiments to see how each method work under controlled circumstance eh?
    we visited your farm and store in Emmaus, Pa, back in 2010, it was very nice, and people very polite and friendly to us visitors from Hawaii. Thank You!

    Namaste, Hare Krsna and Aloha from Hawaii…note: we accept volunteer work exchangers/interns/visitors/workers on our farms.. we have free cabins available…and are open all year long! We have job openings for noni harvestors and farm laborers.
    and email us for more info an application:

  6. Trina

    Very much looking forward to your next post on this subject! Please include information about vermiculture, using eisenia fetida, red worms.

  7. Dale

    I’m very interested in the vermiculture involved composting. I have been doing research with a system that I believe will turn dead soil into organtic farming in about a year using worm tea. We obtain the tea directly from the worm bin with total aeration so it is all freashly obtained from the worms. I suppose if you were to find a combination of ingredients for a particular plant then controlling the break down into compost would be the next step. Turning the compost at designated intervals may help but, having a biologic organisim(worms) breaking it down may be more consistant.

  8. james.c

    ‘maybe’ composting, far from being that shit you threw down the bottom of the garden last year and now looks about done ( drawing a comparison with low quality human foods there) could actually be much more akin to say a nice real ale or an artisan cheese, for soil life and plants that is. I was cooking the dinner earlier and it just occured to me, why should compost making differ that much from cooking, from brewing e.t.c within the right context, in terms of methodology, in terms of quality of ingriedients. In uk gardening books it’s generally accepted that when making leaf mould, the best leaves to use are oak which makes sense. there is more bio-diversity associated with the native oak than any other tree, it can play host to around 250 different species of insect in an old forest. So, if i was going to choose one form of carbon over another to make ‘gourmet compost’ ( sinister marketing opportunitys here, capitalists and none capitalists take note) would i choose fallen native oak leaves or shredded card or newspaper as my first choice or would it simply come down to the structure of the different components that made the real difference?

  9. Ron

    Interesting start, but it did not really tell us anything about making a better compost. No mixes, no formulas, etc. I find most of the articles on here leave a lot to be desired about actually answering the questions they start.


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