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 (http://www.nytimes.com/2009/09/24/garden/24garden.html) 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 (http://www.uos.harvard.edu/fmo/landscape/organiclandscaping/) 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.

33 thoughts on “If Harvard Says That It Works Then It Works Dammit!”

  1. Bravo Jeff! As I like to point out to people, nature creates its own compost tea by rainfall trickling through compost used as a mulch. Gee, how simple! What riles me is that the carbon footprint of this practice is conveniently ignored. It takes ENERGY to continuously aerate this stuff. People that apply it to other peoples landscapes use ENERGY to drive there. But somehow we just can't let nature do the work for us.

  2. We (the peoples) like tea, the process of making tea is nice and soothing; so it seems like such a pleasant and thoughtful thing to do for our plants. Maybe the popularity of compost tea is due to a bit of anthropomorphizing, perhaps? Just my theory.

  3. Holly, I think you're absolutely right. The natural, nurturing appeal is a big part of the sales pitch. Believe me, marketing the stuff as "compost leachate" sure wouldn't work.

  4. After reading the original article, I nearly blew a gasket – coming immediately to the same conclusion as you, Jeff.

    It's this kind of silly stuff that appears online and in the regular press that makes this blog effort developed by the four of you so important.

    Also, if you take a real close look at the picture of the turf under the tables in the online article, you'd see that it's pretty thin. There isn't a compost tea, fertilizer or other magic potion in this world that can make turf grow more vigorously in the dense shade of large trees that's also exposed to constant foot traffic, especially when the soil is damp to wet!

  5. It verges on 'magical thinking' when people believe this stuff works, or the very least, misplaced attribution, like you said, Jeff. I did chuckle to myself about how Harvard had been doing all these other wonderful turf management practices, but attributed the difference to compost tea. It's quite bazaar. It's like fixing someone's broken arm with a splint while doing a rain dance, then attributing the knitted and healed bone to the rain dance! Some people really have no idea.

  6. I've always thought that the piling of mulch around tree trunks comes also from that nurturing impulse (as much as from the impulse to sell as much mulch as possible) — people think that if they put a nice mulch muffler around the trunk they're protecting the tree from winter cold. We do like to anthropomorphize the rest of the world….

  7. I've always resisted the mania for compost tea. It sounded like way to much work – and how could I possibily employ something like that over acres of garden? So I'm very glad to hear the whole idea has no scientific rational behind it. Great blog!

  8. What I can't understand is the many expert gardeners who are swearing by the stuff. Just met another one the other day. Is there a compilation of research findings on compost tea somewhere?
    Oh, and does your blogging program allow links? (Hint).

  9. Linda has put together a compilation of articles. I don't know why expert gardeners swear by the stuff — but I suspect that it has something to do with the fact that the best gardeners aren't necessarily the best researchers (and vice-versa). In terms of the links — I'll figure it out eventually….

  10. I have to agree with the 'anthropomorphizing' theory about the appeal of compost tea. I'm with Holly, it seems so appealing to do something nice for the plants. It's wonderful to have this research to refer to!

  11. Thank you Susan for caring enough to read our blog! We're building a great group of bloggers and all four of us enjoy what you all have to say.

  12. I spoke to a botanist about compost tea and he pointed out that you can't really do a controlled study because all compost is different and the results are dependent on the compost you start with.

    I also worry that there is a danger of Ecoli, when using compost tea on edibles that isn't widely publicized.

  13. OK, so where's YOUR data? All I see is a lot of smug sarcasm. Give us some science. That's your job. I can be convinced either way. As soon as somebody comes up with some good data I'll get on board with their argument. The advocates of compost tea haven't done it. Neither have you. Nor has anyone else, I assume, since you don't cite any research. Why is horticulture so afflicted by bad science and no science at all? Step up to the plate, folks.

    Owen Dell, ASLA
    Santa Barbara, CA

  14. Owen, feel free to access my compiled literature on the topic (which Jeff referenced in the comments above). The little research that has been generated has not given consistent results, and in some cases has had negative effects on the health of the treated plants. If you go to http://www.theinformedgardener.com and click on "horticultural myths" you'll find both the compiled literature and several online articles I've written over the last 10 years.

  15. Thank you Linda for a source of information. I'll have a look. Reading through all of this one more time I find that yours is the first link to substantive information, to the degree that it exists. It truly sounds like the jury is out on compost tea, far as I can tell. But I'll be eager to see what you have to say in your articles.

  16. There's so much nonsense about so many miracle cures for soil and plant problems, I could scream. Fortunately, we have Linda to set us straight with the science.

  17. Owen, you're most welcome and I'm glad you found the information useful. Every few years I'll update the literature and if there's anything new in the other direction it'll be included. Bracey, you make me blush! Thanks for your kind words.

  18. Compost Tea works for FERTILITY. An additional organic pesticide is usually needed to control certain pests. Its the same 2 step process as conventional lawn maintenance- chemically fertilize and broadcast spray a broadleaf pre/post-emergent herbicide, or spray compost tea and use a natural pesticide spray. From a natural perspective, you are adding organic materials to the soil, instead of killing the microbes with synthetic chemicals. This has an overall positive effect on soil composition, *THE BASIS* for plant health and its ability to defend itself against pests and diseases. By the way guys, do you think Harvard or anyone with a proven recipe for compost tea would broadcast it over the internet? This is proprietary information folks! People are going to be able to charge a *premium* for compost teas over synthetic fertilizers. The process is simple and inexpensive. Simply take nature and tweak it a little. Nature will appreciate the 75 cents in electricity used to aerate each batch. Compost teas help facilitate an overall better growing environment. If you need proof in pictures, don't hesitate to ask! (No, you cannot "have" my recipe)

  19. Hi Russ. Thanks for your comment. Here's the thing — I really don't care if you, Harvard, or anyone else gives us their recipes (though, actually, Harvard does give you their recipe online). If you haven't run a replicated experiment then we're not going to care what you think of compost tea. That's the way researchers are — they demand evidence. Without it we simply won't believe you. A picture of a happy lawn or garden is meaningless. I've seen plenty — both with and without compost tea.

  20. I absolutely approve of your need for solid evidence. However, Harvard has switched from fertilizer to compost tea and reduced the amount of water needed by 30%. I don't care about any of the other benefits other than water reduction. The root growth is much deeper, so more water is absorbed. I am not sure how you are addressing this other than rolling your eyes. So, are they lying, mistaken or right? Because is has to be one of them.

  21. Hi Noah, As I mentioned in the article above, Harvard started doing a lot of stuff that has proven to be useful (like aerating and and adding compost to the soil) along with using the compost tea. It seems much more likely that these practices are causing the benefits that you mention rather than the compost tea. If it is indeed the compost tea providing these benefits then that needs to be proven using research methodology.

  22. Why all the bickering – just try it for yourself. Control group against a compost tea group then draw your own conclusions.

  23. I am a Physical Therpiast and live by evidence based practice. I fully believe in the research, but I also know that there are just some things that cannot be “proven”. I use a specific technique that is tailored to each individual and can be different every day. While I do not have research evidence that it works, my kiddo all walk. They have neurological insults (brain damage) and there is no way to know who will and will not walk due to the insult. It is all unknown, and unresearched. So, should I abandon the treatments that I know work because there is no research to support it? In the physical therapy circles I run in we say a lack of research doesn’t mean it doesn’t work. It only means we haven’t figured out how to prove it yet. I know you think that nutsedge doesn’t respond to molasses, but in my yard, it does. I use only organic fertilizer and molasses about once a month. I also have no fire ants. Can I prove that it is the molasses, no. But, do I see results? Absolutely!

  24. Science is obviously critical to mankind. But the rampant amount of boastful posts like this one, in which authors claim to not only know all there is about a subject matter as well as how to test for things that may be beyond there current understanding, shows a woeful ignorance of history. The myriad of times when science has had to catch up to the complexity of a system that is beyond current human understanding IS well documented. To say there is not anecdotal evidence at this time with our current means is tolerable. But to say its bullshit because we are all knowing about agriculture at this point in time makes me question your ability to educate young people to question and probe the unknown and the opportunities that only exist by doing so.

    1. Jeff writes with a certain amount of tongue-in-cheek. The fact that compost tea is STILL not supported with rigorous science speaks more to the lack of efficacy of the product than to the writer’s supposed lack of knowledge.

  25. I have been using both recipes from Harvard after reviewing their website. Studying ecology and applying these strategies in the field are needed to improve our understanding of ecology, which is harder to study. I have used the teas to aid in my various strategies in managing lawns and in applying it to stressed plants and soils.

    Not all compost is the same pH and may be treated at higher temperatures to reduce weeds and may kill some microbes.

    The tea is a concentrated form of microbes and has been very beneficial. I am a landscaper, who uses lots of science to support my work, but we are learning all the time. Some compost is also shredded to a single size so it does not have the needed soil structure to promote good aggregation.

    Why not use the current knowledge? Sometimes science can focus so much on one part of the “elephant” that we spend our whole lives waiting for more research. Let’s keep the practitioners using it as a way to increase soil biology and get the soil restored.

    We don’t have time to bicker over the difference. Chiming in from Bend Oregon, Yvonne
    PS, I have been teaching my gardening crew Linda, from your Great Courses program.
    Thank you,
    Yvonne Babb, Your Garden Companion, LLC

    1. Dr. Jeff Gillman wrote this blog post in 2009. In the 12 years since, there still is no reliable science supporting the use of compost teas of any stripe. Water is the main, and most important component. Nothing else has any measurable effect on plant health or soil biology. In contrast, a good organic mulch, such as arborist wood chips, has been repeatedly demonstrated to improve plant health, soil biology, and weed suppression. We first published on this application in 2005 as part of an ecological restoration project and the science behind the benefits of wood chip mulches has only gotten more robust.

      (Glad you are enjoying The Great Courses series. It was fun to do.)

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