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Is Compost Tea Organic?

You are probably sitting there thinking – is this guy crazy? Compost is organic and so the brewed tea from compost or manure must also be organic. Read on and I just might convince you that compost tea is NOT very organic!

compost tea brewing

compost tea brewing

Compost Tea vs Manure Tea

Before I get started, let’s review some terms. There is both a manure tea and a compost tea. Since neither is a term used by the scientific community or governments the terms are not well defined and they are used to mean a variety of things.

Some proponents of the tea suggest that the term compost tea should only be used to refer to tea that is brewed with the addition of oxygen. Others don’t agree.

Consider that aged manure becomes compost. At what age is it still manure, and when does it become compost – hard to say. In fact so called finished compost made from manure is still mostly manure–complete composting takes many years (ref 1). So manure and compost are not all that different – they are both sources of organic material that contain nutrients needed by plants.

The tea can be made in two ways, as explained in my post called Compost Tea, with or without oxygen. These two methods do produce different results and the method of brewing is more important than the source of the organics.

A recent study compared ACT compost tea to using just compost and is described in Compost Tea – Does it Work?

What is in Compost Tea?

Compost tea is made by soaking manure or compost in water for a few days or weeks. The water becomes brown just like the tea you brew at home. Once the tea is ready, you remove the water leaving behind the nasty manure bits. The water is the tea and is used to water plants.

Some say this makes a ‘tremendous liquid fertilizer’, but as I discussed in the Compost Tea post, that is a highly exaggerated statement. I had a close look at the NPK values in the post Compost Tea NPK Values. So what is in the tea? To understand this we need to better understand manure.

Manure contains animal bedding – the hay and straw used to house the animals. Manure also contains a lot of undigested grass, hay and other feed given to the animal. This is especially true of horse manure since these animals have a very inefficient stomach. Manure also contains digested and partially digested material, as well as urine.

Urine is mostly water that contains soluble compounds. Soluble means that they dissolve in water. Think of the sugar in your tea. When water is added to the sugar, it dissolves in the water. It is still there, but you can’t see the solid form any more.

Nutrients like potassium, nitrate, nitrite etc are soluble and easily dissolve in the water during the brewing process. Simple sugars are also dissolved, just like in your home brewed tea. Phosphorous is notoriously insoluble. Most of it will remain as a solid in the manure and does not dissolve into the tea very well.

The vast majority of the manure is in the form of large molecules such as protein, starch, carbohydrates, fats etc. Large molecules like this are mostly not soluble. Your pasta does not dissolve when you cook it. The same is true for the undigested straw and grass left in the manure.

What this means is that the only thing that dissolves in the tea are simple molecules like the nutrients your plant needs.

Compost Tea is Not Really Organic!

Tea contains nitrates, nitrite, potassium and other minor minerals. It contains very few organic molecules since these are too large to dissolve in the water. They remain in the sludge at the bottom of the pail.

Since the nutrient molecules in tea are no different than the nutrients in commercial fertilizer which is considered to be non-organic, one must conclude that the manure tea is also non-organic.

It is true that the tea does contain some organic molecules, but that is never mentioned by the proponents of tea. The reality is that the vast majority of the ‘good’ organic value of manure or compost is sitting in the bottom of the pail and not in the tea.

Making manure tea is an ‘Organic Sin’. To better understand this, see my next post called Manure Tea is an Organic Sin.

References:

1)What is Compost: http://www.gardenmyths.com/compost-compost/

2) Photo Source: Urban Organic Gardener

Robert Pavlis
Editor of GardenMyths.com
I live in southern Ontario, Canada, zone 5 and have been gardening a long time. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

I hope you find Garden Myths an educational site that helps you understand your garden better.

10 Responses to 'Is Compost Tea Organic?'

  1. I made several batches of compost tea, starting with a few cups of compost stirred into a watering can and adding a couple of teaspoons of sugar. Stirring every now and then produced a foamy, microbe-rich soup in a day or two. I poured it on my plants several times and noticed no miracles.
    It was fun to see the microbe population explosion but know there had to be a population crash once on the soil. Are dead microbe bodies more palatable to plant roots than compost? That would be the only possible change – the NPK content was already there.

    • A recent study makes me wonder if in fact there is a microbe explosion in compost tea. In any event, plants can’t use dead microbes any more than they can use dead plants. Both have to be decomposed into nutrients before plants can use them. Once that happens they do feed the plants.

  2. Robert, enjoyable and informative, but I think you are splitting the wrong hair. “Organic,” both in common parlance and, as I understand it (which admittedly ain’t much), as a legal term (in the US, where I live), orients around methods of cultivation. This differs from the chemistry use of the term oriented around carbon-based (mostly) molecules.

    Subsumed under this orientation of methods of cultivation are concepts that have to do with the source, and method of manufacture, of inputs such as fertilizer.

    For sure, there is no strict consistency in how the concepts are applied. But anywho…

    The relevant point for this blog post is that an input, such as manure tea, may be organic–as understood as a methodology–even when it is non-organic in terms of the molecular constituents.

    Also, a clarifying question. Do you mean in the post that you prefer to call your tea “manure tea” even when the material you submerge in water is fairly thought of as compost? I get your point about there being no clear line between when a pile of poo changes out of poo-ness and into compost-ness, but even still… at some point in time, everyone will agree that it has become compost. Plus, what about compost that was never manure in the first place. Do you call tea from that stuff “manure tea” as well?

    • Robert Pavlis says:

      The comment that manure tea is not organic is a bit tongue in check. You are correct that as an organic method manure tea would still qualify as an organic ingredient. the key is that the stuff left in the pail is the real organic component.

      One of the main problems with compost tea and manure tea is that the source ingredients are never defined well. Even if it is cow manure – the manure quality really depends on what the cows ate, what bedding they used, age etc. How do you define such a thing in the home gardening world – you can’t. In all of my comments about tea – it does not really matter what the original source was. Since tea is not really very beneficial for the garden the source is immaterial.

      • My thick headedness for taking you at face value and not noticing the tongue between the lines of your cheek.

        From lectures I’ve attended, garden tea (my new offer for a neutral term) can have beneficial value, but that depends strongly on two factors: first, what are the soil/plant conditions you want to affect ; second, how do you make your tea. The basic difference between different teas, in terms of the effect they will have, has to do with the ratio of fungal to bacterial organisms it contains (assuming high numbers of organisms in the first place). Other factors matter, but this is the basic divergence between teas. But whether, for example, a relatively fungal tea will be beneficial depends on what the preexisting soil biota conditions are and what are the conditions that most benefit the crop(s) you want to promote. Different plant species react differently to different soil biota conditions. Some plants benefit strongly from mycorrhizal associations, others not so much, etc. Also, the biota ratios will affect soil pH.

        So–says the lecturer–you can reduce weeds and promote crop vitality with a tea IF the weeds you have tend to prefer one sort of soil condition, your crop(s) tend to prefer another, AND you brew your tea (via properly chosen source materials and properly chosen brewing method) so that the result nudges the soil condition away from the sort enjoyed by the weeds towards the sort enjoyed by the crop(s). Apply the wrong tea, on the other hand, and you’ll get either no noticeable affect or potentially cause more harm than good by making things increasingly weed friendly.

        I suppose you might wonder, “is a garden tea capable of nudging soil conditions in this way?” I don’t know, though the lecturer I heard asserted as much, and presented cases purporting to support the assertion. No reason to keep the lecturer secret: Elaine Ingham, currently chief scientist at the Rodale Institute. I’m not sure if she was at Rodale at the time that I heard her lecture, which was a couple years ago.

        • Robert Pavlis says:

          What you say sounds very logical and your argument is used by many people. Unfortunately it is not correct. I’ll have to do a post on the benefits of adding microbes to soil, but here is a short answer.

          Microbes are very important in soil – they do all kinds of things that affect plants, and we are just beginning to understand what they actually do. Mycorrhizal fungi are also very important in the soil. The question we need to ask is do we need to add more? Will adding more have any affect?

          The short answer is no. The soil already contains all the microbes it needs or can support. Microbes grow very quickly. For example bacteria can reproduce every 20 minutes. If we want more in the soil, we just need to feed them and we will have quickly have billions more. Adding a pail more will have no affect.

          One of the biggest problems with garden teas (I like that term), is that the home owner has no idea what they are brewing. They could just as easily be brewing a pathogen that will kill the plant, or harm themselves. Even if the right microbe could improve the soil or benefit a crop, the chances are slim that your tea has it. And if it had it in the first batch, there is no guarantee it has it in the second batch you make.

          There is a great interest in not introducing foreign plants into our local environment. Why then would anyone suggest introducing a foreign microbes to the local soil? Garden tea could do just that.

          Do microbes alter soil? yes. They improve soil structure, and they add nutrients to the soil. Do they alter pH? No. The pH of soil depends on the minerals in the soil. Adding microbes, pine needles, and all the other home remedies have no affect on soil pH. Adding large quantities of certain chemicals can alter soil pH in the short term.

          Current research has shown no consistent benefits from garden tea.

          Elaine Ingham seems to be associated with Earthfort – a company selling garden tea type products and books/CDs written by Elaine Ingham. It always makes me suspicious when someone promotes an idea to sell their own products. Rodale institute has done a good job promoting the ‘organic movement’, but unfortunately they are an extreme group and sometimes looses sight of the facts.

          • I know that prior to being at Rodale — or maybe concurrently? — she was the founder and head honcho of Soil Foodweb, Inc, which I think is a consulting business. I agree that evidence is more suspect than usual when coming from a source that has a profit motive in the mix.

            With that in mind, Ingham’s claim was that soil biota can affect soil pH through their secretions. She might claim additional pH effects as well — as I mentioned, I heard this at a weekend lecture event, which covered a lot of rough ground quickly. What I recall her saying was that fungi secrete acidic compounds–if I understand correctly, they effectively digest their food outside the body with these secretions, then absorb the broken-down nutrients. Less from memory than from implication, bacterial secretions are more basic. So if the soil biota are heavily fungal, their secretions will be part and parcel of creating and maintaining the acidic environment, and vice versa for bacterial soils. The extreme version of her argument is that any given mineral base can coincide with any soil pH (within the relevant range), so long as the “right” biota are present to work their biochemistry.

            I think her argument was that the compost tea (her usage) was able to nudge the growth patterns of the soil biota, not so much necessarily that it would increase the number of organisms, but nudge the relative populations of this or that species/class/family toward a new balance. She stressed that she prefers to use whole compost, but when dealing with large acreage turns to tea for simple practicality.

            She also stressed a point similar to yours, that any random compost pile, and subsequent tea, would contain any random assembly of organisms. (Well, not exactly random — the organisms would be those preferentially sustained by the random source material.) But she claims that a person can fairly reliably direct which types of organisms are promoted through selection of source material and treatment of those materials during the composting process.

            Anyhow, I’ve just plugged “ingham soil” into Google scholar and the only articles of hers that pop up are pre-1990s. None appear (at least in the first few pages of links, before I got bored of looking) to address this question. If she has peer-reviewed evidence backing up her claims, I don’t know what it is. So while I’ll hold out hope that I can compost my way to a perfect garden (I mean, I’m making the compost anyway — it would be nice if it helps improve things), I’ll hold back on describing compost as the be-all, end-all.

            Plausibility sure is a double-edged sword!

          • Robert Pavlis says:

            Fungi might excrete acids, but that does not mean they affect the soil pH. Rain even without pollutants in it contains CO2 which forms carbonic acid. This is quite acidic and has been falling for millions of years. The soil is still not acid due to this rain.

            Compost might alter the soil microbe populations, and probably does. But the only way to know the details is to have quite an extensive lab going.

            Compost tea might brew a particular population of microbes while it is being brewed – I agree with that. But once these microbes are poured onto the soil, the population will return back to the one that is best supported by the soil. Since the tea ingredients are minimal compared to the soil ingredients, the population will match what is already in the soil, not what was in the bucket of brewing compost.

            Compost is a valuable ingredient for most soils. But even this can be problematic if you add too much. An organic content of over 5% has been shown to cause problems – this is not a concern for most gardens unless you are making huge quantities of compost.

        • Mariano Torres says:

          There are many different opinions, and not many scientific facts regarding the use of compost tea. While anecdotal evidence and claims can be exciting, it’s important to step back at times, to unearth what we really know and understand.

          There have been many excellent scientific trials testing the effects of compost, which provides a good base for understanding compost tea.

          What we DO know about compost is:

          Compost is a great soil amendment. It:

          Improves soil structure, porosity & density—provides better root environment
          Loosens up clay soils for air & water
          Helps sandy soils retain water & nutrients
          Helps prevent runoff. Only a 5% increase in organic material quadruples soils water holding capacity.
          Makes any soil easier to work
          We also know compost:

          Adds essential nutrients & soil microorganisms
          May reduce incidence of plant diseases & other harmful organisms.
          Compost is comprised of a very large & diverse community of microbes, humic acids, chemicals, which varies wildly from compost to compost. Different feedstocks, different methods (thermophillic vs. mesophillic vs. vermiculture) and different climates are just three variables that change the organic and chemical outcome of compost. Compost brings and feeds diverse life in the soil. We know that these bacteria, fungi, insects, worms, chemicals, humic acids and more support healthy plant growth.

          Although not a fertilizer, compost does have a positive, cumulative effect on soil nutrient levels. Whatever nutrients are present in the soil become more bioavailable to plants growing in soils with added compost.

          There have been many studies that support all of these benefits of compost. There is also recognition that different composts can affect different crops in very different ways.

          Compost tea research is more recent. Again—it has been documented that compost tea has a very large & diverse community of organisms, depending on the compost, method of brewing and temperature among other factors.

          While there have been some scientific studies which show a positive effect on certain crops, there are also some studies which show a negative or no effect on certain crops. Some of these studies suggest that the effects are nutritive; others suggest that there may be some disease suppressive qualities in certain compost teas. On the compost website (http://www.whatcom.wsu.edu/ag/compost/), links to some of these studies and discussions are under the “Compost Uses” section. These include a link to an Organic Farming Research foundation Information bulletin which includes a review of recent literature along with several controlled experiments, a review of compost tea trials on the Appropriate Technology Transfer for Rural Areas (ATTRA) site, and an article by Linda Chalker-Scott of Washington State University, “Compost Tea: Examining the science behind the claims.” In the “Research and Publication” section, a published study designed by IPM Manager, Todd Murray in cooperation with Cascade Cuts Nursery, “Brewing up Solutions to Pest problems” describes the trials and outcomes of compost tea on basil.

          Some people have tried inoculating compost teas with specific beneficial organisms. While this may help, it is still hard to be consistent, since those beneficial organisms need the right environment to maintain high populations in the brew. In general, the effects of inoculants are very short lived as the native, adapted organisms quickly reclaim their niches within the system.

          There is also a controversy over whether compost teas should be produced with or without aeration. Much of the literature refers to this as “anaerobic” vs. “aerobic” teas. Teas without aeration are made with placing compost in a permeable “bag” soaking it in water for 24 to 48 hours. Teas with aeration are made with air bubbling through the compost tea mix continually, and take less time to brew. Again, although many people support the “aerated” approach, saying that those active systems push the beneficial microbes out of the feedstock & into the tea, a number of studies and researchers suggest that anaerobic teas may actually have greater disease suppressive capabilities.

          The USDA has some concern over human health issues. They do not encourage people who are growing uncooked edible foods to spray with compost tea, due to the possibility of inoculating food with e-coli, or other harmful pathogens possibly living in the compost tea mixture.

          Confused? So are most of the rest of us! What we DO know is:

          Right now, the community dynamics of compost tea is not understood or currently controllable. Thus using it as a reliable amendment is difficult since benefits are contributed through many factors (chemical, nutrient, microbiological) instead of known active ingredients.

          Hopefully, as we do more research we can provide this information to folks interested in the technology so they can make good choices.

          So despite all they hype, compost tea is not the silver bullet everyone is looking for. Unfortunately, nature is not that simplistic. But it’s fun to experiment. (I do lots!) If you do experiment, and come up with a formula that you think works—try replicating it in a scientific way, and let us know the results

          • Robert Pavlis says:

            Excellent post! I agree with much of what you say.

            Keep in mind that ‘compost’ and ‘compost tea’ are quite different. Compost is an excellent addition to your soil and does not have the same concerns about health that compost tea has.

            Home made compost does contain a variety of microbes. Store bought compost may have been sterilized in which case it does not contain microbes. The existence of microbes in compost is not really important for the garden since the native soil microbes will take over once the compost is added to the soil.

            I disagree that compost is NOT a fertilizer. Compost contains nutrients that are immediately available to plants, and it contains the organic material that will be converted to nutrients in the future. Compost is a slow release fertilizer.

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