Pennsylvania is for…..Snake Oil?

This year at the Philadelphia Flower Show there were a few groups talking about compost tea.  Meadow Brook Farm, a farm owned by the Pennsylvania State Horticultural Society is one, and another is F2, a company that provides “Scientific Soil Management”.   Apparently they do things that are good for the soil, though the “method” section of their website is a little too vague for me.  They also offer pictures of the results they’ve had with compost tea on a few different projects.  The one that was most interesting to me was the Rose F. Kennedy Greenway.  You can see it here.

Look at the boxwood comparison and you tell me why the compost tea didn’t do a darn thing.   Look at the grass comparison while you’re at it.

Throughout the Pennsylvania Horticulture Society’s website there are all kinds of opportunities to find out how to make and use compost tea, including courses at Meadowbrook farm.  Now that Elaine Ingham is at the Rodale Institute (Which is in Emmaus Pennsylvania) they have all kinds of classes on it there too.  Even Longwood Gardens is Getting into the act (scroll down and click on the compost tea link).  So what I want to know is, why have the Compost Tea Gods invaded my home state of Pennsylvania?  What makes the keystone state so attractive to people who want to promote snake oil?  I just don’t get it.  Is it the cheesesteaks?  Maybe the scrapple?

No, I’m pretty sure it’s the Rolling Rock….or maybe the Yuengling – America’s oldest brewery (their Black and Tan is one of the best beers in the US – second only to anything brewed by the Surly company).   Yeah, that’s gotta be it.

Parking tickets, compost tea, and pseudoscience in the Ivory Tower

Back in November 2009, Jeff posted an educational and amusing commentary about Harvard’s use of compost tea. Much vigorous discussion followed, and we’ll return to that topic in a moment. But first, I’d like to tell you about my morning yesterday.

In September of 2010, I received a ticket for parking longer than 2 hours in a restricted zone. Now, there was no way I committed this infraction; I had hard core proof that could not be rationally challenged. So, armed with my husband’s affidavit as to my whereabouts, as well as a dated receipt showing I was at the post office at the time when I was apparently parked several miles away, I went to court to challenge the ticket. During our briefing, the sitting magistrate told us we would need to provide a “preponderance of the evidence” to win our respective cases. For me, it was an anticlimactic turn of events, as the citing officer (whom I’d subpoenaed) did not show up, so the ticket was dismissed for lack of evidence.

And thus we return to today’s subject – use of compost tea without a “preponderance of the evidence.” Jeff took Harvard to task for buying into this “bullpucky”, I think he called it, and now Berkeley has decided to drink the Kool-Aid. One of my dear colleagues at University of Washington forwarded me a link announcing that Berkeley Botanic Gardens was adopting compost tea as an “eco-friendly fertilizing method.”

As the article reports, compost tea is being used

1) as a disease suppressant
2) to provide nutrients, and
3) to reduce the amount of water needed.

I’ve written a lot about compost tea, and I’ve reviewed journal papers on the topic as well. In a scientific nutshell, there is no solid evidence to support use of compost tea, particularly aerated compost tea, in disease suppression. Likewise, there is no evidence to support a nutritional role (I just finished reviewing a manuscript on this topic and the data were unconvincing). Finally, I cannot understand why spraying compost tea onto the leaves of a plant would reduce its water requirements. The “preponderance of evidence” is truly lacking.

Students at Berkeley have the dubious honor of supporting this nonsense through their student fees: $11,000 has been spent on a 300 gallon tank, worm composting bins, and a spray tank.

Whatever happened to using good old compost, and letting nature create its own “tea?” (Compost used as a mulch also helps reduce irrigation needs.)

Compost tea…again

My not-fan Justin has emailed me again with some more substantial comments of my criticisms of compost tea.  I’ve posted his email here, along with my responses in a point-counterpoint format:

1.  “Compost teas do vary from batch to batch, the same way galaxies vary.  Without the complexity and biodiversity present in the tea, you might as well just be using water.”

Yes, they do vary, and this is why it is so difficult to conduct replicated and repeatable studies on the efficacy of compost tea.  The comparison to variability in galaxies is really not relevant, nor is it conducive to experimentation.

2.  “Generally speaking though, this can be overcome by the purchase of virtually any microscope capable of achieving 400x field of vision or greater. By looking at what is present in the tea and a little bit of background knowledge, one can make an educated decision as to whether or not it will improve conditions on one’s plants and soil.”

Purchasing a microscope does not overcome variability.  Furthermore, microbial species can’t be reliably identified simply by looking at them under a microscope.  The “little bit of background knowledge” is vague.  What, exactly, will help in making the “educated decision” in whether it will do any good to use it?

3.  “I assume that these steps were not taken in these experiments, because of the generally lacking method in what has been come to be labeled (tobacco science).”

The steps referred to (I assume in point 2) are not useful in assessing efficacy of a product – in other words, demonstrating an effect not seen in the control treatment.  What would be the control?  Not looking under a microscope?  Not having background knowledge?  An experiment requires experimental variables.  I hadn’t heard of  “tobacco science” and had to look it up.  Apparently it’s “science that is skewed or biased, especially toward a particular industry.”  The only industry I see in this discussion is the compost tea industry – and yes, it’s an industry.

4.  “First of all you are trying to disprove compost tea as a foliar pesticide only. You do not do a relatively new science justice by not looking at the wholeness. Any and all foliar applied pesticides are palliative in nature, and symptoms will recur if you do not deal with the source problem. Compost tea (aerated) is to be used in the rhizosphere first, foliage second, and surrounding environment third. If you are not talking about this mode of application, you are not talking about compost tea.”

Compost tea is not a new science.  It is a product.  To demonstrate efficacy of a product requires conducting a controlled experiment in which there are one or a few variables.  It’s not possible for science to look at the “wholeness” of compost tea – it has to be looked at systematically.  Neither is compost tea defined by its mode of application.

I do agree with Justin, however, that symptoms (of disease or whatever) will recur if the underlying problem isn’t addressed.  There are scientifically testable, consistently reliable methods for improving soil health and plant health. At this point, compost tea is not one of them.

5.  “In order to disprove compost tea, you must first explain to the reader how balances of microbial life (bacteria, fungi, protozoa, nematodes, microarthropods, earthworms) are different in various stages of ecological succession. You must describe how the OVERALL HEALTH of any plant depends on how it has evolved to live in the soil conditions in which it is planted. You must describe how human activity effects soil food webs and how soil disturbed or treated with substances toxic to microbial life will move the soil backwards in succession. This will create a soil that favors weeds over crops by reverting the soil to bacterial dominance.”

Disproving any hypothesis (e.g. “compost tea prevents foliar disease) relies upon scientific evidence.  What Justin is asking for is not experimental but explanatory.  (There are several inaccuracies in what he outlines above, but in the interest of sticking to one topic I’m ignoring them.)

6.  “If you are going to debate compost tea you must disprove its ability to create a more fungal soil and inoculate the rhizoshpere with arbuscular mycorrhizae, improving soil born nitrogen. Excuse me, soil born proteins in the form of microbial biomass that are released as ammonium or nitrates in detritus, when consumed by predatory microbes, that are generally found to be lacking in human disturbed soils.”

The first point is incorrect, and is one of the hallmarks of pseudoscience – reversed burden of proof.  It is up to proponents of compost tea – or any other product or practice – to demonstrate efficacy.  (Wikipedia has an excellent overview of the characteristics of pseudoscience.)

7.  “You must prove: that most garden or Ag soils have a stable food web, the food web is not necessary, or that compost tea does not create a more complete food web. You must create a fair experiment (not paid for by cargill) that tests foliar applications on crops planted into a healthy rhizosphere with a complete food web.”

No.  Compost tea proponents must demonstrate that compost tea has an effect.  Period.  (It’s also important to understand that science doesn’t “prove” anything.  It either supports a hypothesis or disproves it.  That’s why scientific inquiry is a dynamic process – you never know when new evidence will lead to a paradigm shift.)

8.  “If you cannot present your findings in this way, you are misleading your readers knowingly. I was raised to classify that as a lie.”

I don’t conduct these compost tea experiments (though I do conduct research in other areas).  Part of my job as an extension educator is to read the scientific literature and translate it for use by nonscientists.  I have posted an extensive bibliography of the compost tea literature on my web site.  If I were either deliberately or accidentally misleading anyone, I would be in serious trouble with my university.  Given that I started my criticism of compost tea on my web site over 10 years ago, it’s likely that the information is not misleading.

Two new postings on compost tea efficacy – and safety

We just don’t have enough excitement on the blog, so I thought I’d bring up two new items that just crossed my virtual desk.  The first is today’s Garden Rant posting from Susan Harris.  I won’t spoil her well-written blog, but if you’ve been following the debate on the disease-control properties of compost tea, you’ll be interested in reading it.

The second was in an email from a colleague at the EPA on a new journal article.  Here’s what he said:

More potting soil and Legionella, this time in Scotland.  (Eurosurveillance, Volume 15, Issue 8, 25 February 2010).  Note that “other countries where L. longbeachae outbreaks have been reported” includes the U.S. but there is no required labeling here, though it is in Australia, New Zealand and possibly much of Europe.  Also note the association of Legionella mainly with droplets, and the possible connection to compost sprays as seem popular among do-it-yourself pesticide makers.

“The exact method of transmission is still not fully understood as Legionnaires’ disease is thought to be acquired by droplet inhalation. The linked cases associated with compost exposure call for an introduction of compost labeling, as is already in place in other countries where L. longbeachae outbreaks have been reported.”

Friday Can O’ Worms

I was pleased to see that at least two of you dug into the literature over the weekend to read these papers!  (I can still remember the first time as a Master’s student when I was assigned a journal paper to review.  I had NO idea what, exactly, I was supposed to be doing.  It took a long time to figure it out.)

In any case, kudos to Jimbo and Diana for their thoughtful comments – and for zooming in on the problems.  Indeed, Jeff and I conclude there is likely a fertilizer effect on the plants – and a healthy plant is better able to resist insects.  Secondly, the speculation at the end of the paper regarding root uptake of phenolics from the vermicompost – compounds that weren’t even measured, much less monitored for uptake – is totally unsubstantiated and in fact is not feasible, given root physiology.  I’ve pasted my draft to the journal editors below, which explains this a bit more.  (Jeff also has some choice things to say, and I’ve added his comments as well.)

From LCS:  “I recently read the article by Edwards et al. entitled “Suppression of green peach aphid (Myzus persicae) (Sulz.), citrus mealybug (Planococcus citri) (Risso), and two spotted spider mite (Tetranychus urticae) (Koch.) attacks on tomatoes and cucumbers by aqueous extracts from vermicomposts” (29(1): 80-93).

“The article presents evidence that the use of vermicompost teas increased the resistance to damage from these pests.  As the authors state “there are many reports in the literature of organic nutrient sources decreasing numbers of pest arthropods.”  This seems a logical conclusion given that the authors have provided an additional nutrient source to their treated plants (vermicompost extract) that was not available to the control plants (which were drenched with water).  The treated plants were better able to manufacture anti-herbivore compounds as a result.

“Yet the authors then venture into unsupported speculation that this resistance was due to the uptake and transport of water-soluble phenols by the roots and into the leaves of these plants.  In the authors’ words:  “these diverse results all point to the probability that water-soluble phenols, extracted from the vermicompost during aquatic extraction, taken up into plants from soil receiving drenches of vermicompost aqueous extracts, could be the most likely mechanisms by which vermicompost aqueous extracts can suppress pest attacks.”

“Not only are there no data or other direct evidence to support this speculation, but the likelihood of such uptake is highly unlikely if not impossible.  The water/nutrient uptake mechanism in plant roots is cellularly regulated, particularly at the endodermis, where all solutes must pass through cell membranes prior to entering the vascular tissue.  No such transport has ever been documented in the literature, though the authors report “There have also been suggestions of these effects being due to the uptake into plants of phenols from organic manures (Ravi et al., 2006).”  This latter paper, however, measures the presence of phenols and their associated enzymes in the plant tissues, not the uptake of soluble phenolics.  Plant physiologists and biochemists have long known that plants are capable of synthesizing a wide variety of phenolic compounds used to ameliorate abiotic and biotic environmental stresses.  I am surprised that the authors did not discuss their theory with plant scientists at their institutions.

“It is disappointing that the authors were not discouraged during the peer-review process from making unsubstantiated, fantastic claims about the mechanisms underlying their research results. ”

From Jeff:  “Though we do not discount the possibility that compounds may have been present in the vermicompost that could have been taken up by the plant’s roots, we think it much more likely that there was a fertilization effect which caused the plants to grow more rapidly and/or which allowed the plant to defend itself more effectively using its own defensive mechanisms. The authors of this paper discount this effect by stating that “It could not be caused by uptake of soluble nutrients since all of the experimental treatments were supplied regularly with all the nutrients that they needed from Peter’s Nutrient Solution, which was applied to the experimental plants three times a week.” but do not include any evidence to back this statement up. This is a fatal flaw. In fact, the authors don’t even provide any data regarding the concentration of nutrients that were added. Simply stating the analysis of the Peter’s fertilizer which was used provides us little data as they could have mixed this up at any concentration before applying. Was nitrogen applied at 10ppm? 600ppm? Likewise, though the authors tell us the concentration of nutrients in the vermicompost used, no indication of the amount of nutrition in the compost extracts is given. If these analyses of nutrient content turned out to be too expensive the authors could simply have grown additional plants without exposing them to the insect pests. By then comparing plants which had been grown with extracts to those grown without the effects of the extracts on growth would have been made obvious. Another significant problem with this paper was the lack of information regarding the variety of tomato which was grown. Tomatoes have various resistance mechanisms to defend themselves from insect pests including, but not limited to, both glandular and non-glandular trichomes. Many papers over the years have shown that the density and chemical composition of these trichomes is affected by both the plants parentage and by nutrient concentration.

“In short, it is difficult to believe that even a novice researcher would provide the paucity of information and experimental data that these researchers did which might elucidate the presence or absence of a fertilization effect. The fact that the first author of this study is a seasoned researcher gives the impression that the objectivity of this research has been compromised. This impression is only strengthened when we discover, at the end of the paper, that this research was funded as a subcontract to a grant for small businesses, in this case the Oregon Soil Corporation. It seems logical to assume that this paper was published as a gimmick to promote the business interests of a producer of vermicompost rather than for any furthering of science. You have done your journal a great disservice by publishing it.”

Friday puzzler: Opening a can of worms

Part of being a Garden Professor is evaluating, interpreting, and passing on good science to the rest of the gardening world.  I was recently made aware of two articles soon to be published in Crop Protection and Pedobiologia, both peer-reviewed, scientific journals.  (You can download these articles just by clicking on the highlighted journal names.)

Briefly, what one expects from a scientific article is (1) a statement of the research question (the hypothesis) to be investigated, (2) a clear description of the materials used and procedures followed, (3) a listing of the results, along with their statistical significance, and (4) a discussion of the results, including whether they supported the hypothesis.


Both articles focus on the use of vermicompost teas as a way of reducing pest damage on greenhouse grown crops.  If you’re not familiar with this product, it’s made using worm castings and water in an aerated system. The researchers conducted one large experiment and divided the results into two parts for publication. Therefore, the materials and procedures were the same for both articles, and you’ll also see that the conclusions are likewise the same.  (My point – you really only need to read one of these articles.)


I sent these articles and my evaluations to my GP colleagues; at least two of us will be sending letters to the editors of both journals expressing our concerns.  Jeff thought these articles provided a great opportunity for our blog readers to look over our shoulders and see what we do.  We don’t question the results that the investigators got, nor do we have any argument with the statistical analysis.  We do question the authors’ interpretation of the results.

So here is your assignment for the weekend:

(1)  Read the methods section carefully to understand the differences between the treatments (the vermicompost tea addition) and the control. Can you think of an alternative reason for the results the researchers found?
2)  What additional flaw do you see in the discussion section in terms of the proposed mechanism of protection conferred by the vermicompost tea treatment?

On Monday, I’ll post the draft of the letter that we’ve drafted to the journals.

Oh, and if you have any questions, please post them!  We will answer them the best we can.

Compost Tea? How About Compost Pee!

My news tab in Firefox is the BBC “latest headlines” page. It’s a great place to get pretty darn unbiased news plus the U.K. equivalent of “News of the Weird”.  SO, relative to our ongoing discussion of composting…here’s a story ripped directly from the BBC headlines. Follow the link for a video (interview, that is).

Disclaimerage: I nor any of the other Garden Professors endorse this activity, nor any claims as to its usefulness, scientific relevancy, harrumph harrumph, etc,. etc,. etc. We do, however, fully endorse garden-related humor!


Pee To Help Make Your Garden Grow

Gardeners at a National Trust property in Cambridgeshire are urging people to relieve themselves outdoors to help gardens grow greener.

A three-metre long “pee bale” has been installed at Wimpole Hall.

Head gardener Philip Whaites is urging his male colleagues to pee on the straw bale to activate the composting process on the estate’s compost heap.

He said the “pee bale” is only in use out of visitor hours, since “we don’t want to scare the public”.

He said: “For eight weeks now, male members of our garden and estate teams have been using the outdoor straw bale when nature calls. The pee bale is excellent matter to add to our compost heap to stimulate the composting process; and with over 400 acres of gardens and parkland to utilise compost, we need all the help we can get.

“There are obvious logistical benefits to limiting it to male members of the team, but also male pee is preferable to women’s, as the male stuff is apparently less acidic.”

By the end of the year, it was calculated that the 10 men from the 70-strong garden and estates team will make more 1,000 individual trips to the pee bale, contributing towards the compost for the estate. The estate said it will have saved up to 30% of its daily water use by not having to flush the loo so many times.

Rosemary Hooper, Wimpole estate’s in-house master composter, said: “Most people can compost in some way in their own gardens. Peeing on a compost heap activates the composting process, helps to produce a ready supply of lovely organic matter to add back to the garden.

“Adding a little pee just helps get it all going; it’s totally safe and a bit of fun too.”

Story from BBC NEWS:

Published: 2009/11/13 00:40:21 GMT


If Harvard Says That It Works Then It Works Dammit!

So back in September my department head (who is, for all intents and purposes, my boss) handed me a New York Times article ( about the grass at Harvard which is now being managed organically.  We share the opinion that many organic techniques, such as compost tea, are “Voodoo Science” (that’s a term I stole from Mike Dirr) and so she thought I’d be interested in the techniques that Harvard was using.  She didn’t say it explicitly, but I think she thought I’d get a laugh out of it.  And I did….Along with a funny feeling in my stomach.

After looking at the article I just couldn’t resist going to Harvard’s website ( and finding out all of the stuff that they’re doing to make their grass look wonderful.  And, to be honest, much of it is great.  They’re aerating more, they’re adding compost to the soil, they’re using fewer pesticides.  All of which I wholeheartedly agree with.

And then they’ve got this whole compost tea thing going on. In fact, they actually include information on how to make a compost tea brewer and different recipes for these compost teas.

For the uninitiated, compost tea is a mix of water along with other things — such as a carbohydrate source (like molasses, or flour, or sugar, etc) and maybe even a little bit of organic fertilizer — into which a “teabag” (usually something like a burlap sack) is dipped which contains compost.  Air is usually bubbled through the mixture, in part to reduce the likelihood of bad bacteria, like E. coli, infesting the mix (research has shown that this doesn’t work).  Supposedly the good microbes from the compost start growing in the spiked water producing a “tea” which is packed with microbial goodness for your plants.  The microbes are supposed to revitalize the soil as well as, potentially, helping it to ward off plant diseases.


This isn’t to say that I don’t think soil microbes are important because I do — they’re vitally important!  But why is it that some people think compost tea is needed to add them?  As a researcher and professor I’m supposed to try to stick to saying what the research supports.  Following those rules I’d like to add to a comment that Linda made the other day.  The research currently shows that compost tea is unlikely to do a darn thing for you — at least in terms of the microbes which it adds.  Compost teas, like the ones from the recipes at Harvard, will often have nutrients in them from the added compost (nutrients will leach into the water from the compost), or from fertilizers.  These nutrients can obviously provide some fertility to the soil (or to the foliage).  Beyond that fertility I am completely unconvinced of the value of compost tea.

So why are the people at Harvard raving?  Well, it looks to me like they did a bunch of good things, incorporated one Voodoo science technique, and then attributed an inappropriate amount of their success to the Voodoo science technique.  Go Harvard!

I’m going to close with an image of some roses (these are a small sample from a larger experiment) that I treated with compost tea to protect them from disease.  Don’t they look nice?  I have a number of researcher friends who have also tried these teas.  None has had a positive experience.