Still confused about compost tea, I turn to Rodale



              Research fields at the Rodale Institute

More thantwo years after our Great Compost Tea Debate between the two Big Jeffs (Gillman and Lowenfels, of course), confusion over the benefits of aerated compost tea (ACT) is only increasing.  At least I'm more and more confused – because I keep hearing raves about the stuff from people who actually use it, despite the lack of science confirming its benefits.

Sure, there's one source regularly cited by proponents – Elaine Ingham – but she seems to stands alone, with her findings still not replicated, and she sells a ton of books, CDs and seminars promoting the stuff, after all.

And look at the line-up of academics on the other side!  Frank Rossi at Cornell says there's "little proof of a major benefit".  Linda Chalker-Scott agrees with Gillman that while there's some nutrient content in compost tea, there's no proven benefit in preventing disease.  Here's how she summed it up [pdf] in Master Gardener Magazine: "Clearly, the science is not strong for aerated tea use on crop plants, much less on lawns, shrubs, and trees." And I recently heard the famous East Coast compost expert, Frank Gouin, agree, adding that even for its nutrient value, compost tea isn't as good as compost itself.

Yet despite all that, we'll be seeing ACT available at lots more retail stores this year – garden centers, Whole Foods and independent organic food stores, even some hardware stores.

So I decided to ask the good folks at Organic Gardening and Rodale to weigh in with the latest and best on the subject.  OG senior editor Doug Hall told me he'd recently researched the subject while editing an article by Mike Shoup, owner of Antique Rose Emporium, who swears by the stuff!  Doug couldn't explain the wildly divergent opinions about compost tea but he IS convinced that "There is the potential for a health hazard" from its use – that being the possible presence of E. coli.  And he's concerned that some Cooperative Extension Service websites happily provide the recipe for making compost tea at home with no warning about the health risks if it's applied to food crops.

So Doug's hoping the Rodale Institute will take on ACT as a research subject – it's right up their alley!  Seconding that emotion, I contacted them and was sent their report on the subject. Here's the conclusion:

Overall, the data
underscore how much remains to be learned about the on-farm use of compost tea,
whether in organic or conventional systems. The widely divergent results in the
three crops studied here suggest that it is difficult, if not impossible, to
generalize about the efficacy of compost tea for disease suppression across all
crop species.

And Greg Bowman, the Institute's communications manager, told me he knows that "the researchers felt that the results did not warrant the
work, variables and risks of using it, relative to just using high-quality
compost to create healthy soil and working on good organic crop
management."  Well, that settles it for me – until further notice.


  1. Personally making compost tea is just another process I am too lazy to deal with. Even if it got an unqualified across the board thumbs up I would still just keeping adding my wood chips as a mulch and letting decomposition do the rest of the work for me.

  2. Great post, Susan. And I’m with Christopher C. Apply a nice mulch and allow nature to produce its own compost tea as it snows and rains.

  3. The only compost “tea” I’ve ever used was goat manure. I used to fill a bucket 1/3 with goat “pellets” and 2/3 with water, let it sit a couple days and used it to water roses. It seemed to work well as a fertilizer. We had a hard time composting the goat waste (both our dogs and the neighborhood dogs thought it was great to roll in, but they tended to leave the soiled straw and hay alone), so making a liquid fertilizer out of it seemed a good way to let the roses get the benefit of the fertilizer and not have to wash the dogs every day. It never occurred to me that someone might think it was great for preventing powdery mildew or other problems.

  4. At the end of the day I think this boils down to any effort at introducing decayed organic matter into the soil being effort well invested.

    I’ve made compost tea with the material in a worm bin, and I’ve inadvertently made it when I had aged coop litter in a bucket that got rained in. The point is that we’re reintroducing nutrients into the soil, and this makes for healthier plants in turn.

    I think the argument that compost tea prevents disease in plants is likely an exaggeration, but at the same time, if using it means really vigorous plants (just like using regular compost does), well of course they’re going to be less prone to problems. It’s not even a worthwhile claim to make. As long as you’re introducing composted material you’re cooking with gas.

  5. You know what really works? Doing nothing. Or, doing nothing once you’ve picked the right plants for your soil and light. In two years every one of my plants have tripled in size. Proof’s in the pudding (soil?) on my website when I did a beginning to present 2 year retrospective of my garden in pics, posted back in December.

  6. The only reason I could see ACT being better than compost itself is if I was growing with hydroponics. If I was using rock wool or kiln fired pellets as my growing medium, which would not be conducive to mixing with compost straight up, then I could see the benefit of ACT.

    Have there been any studies by the aforementioned scientists regarding ACT for hydroponics versus other commercially available fertilizers?

  7. To help untangle the ACT controversy, the first step is to split what the problem into two parts, nutrients vs. microbial ecology.

    The nutrient part is easy. Compost itself is not a concentrated source of plant nutrient ions, such as urea or blood meal to name a couple of familiar N sources, one industrial, one organic. “Tea” is even more dilute, so, no, any benefits probably don’t occur from ‘foliar feeding’.

    Moving from molecules to microbes is a huge jump in scale. Ingham suggests that a correctly brewed ACT engenders high levels of beneficial microbes. These are supposed to suppress pathogens , plant and human (even dangerous strains of E. coli, most forms of which are not dangerous, Doug), through competition and create a beneficial microbial ecosystem with many positive effects on the overall plant-soil-organism complex, including enhanced nutrient availability and greater disease resistance.

    It is an appealing concept, and there may be something to it, though I agree it needs careful study. A suggestion that there may be something to it comes from commercial composting, where you can now purchase strains of bacteria and bacterial enzymes for particular applications. Maybe it is possible to do something similar with growing plants and soil.


    I also like the underlying idea that the soil’s microscopic ecology and diversity are just as important as the more easily observed diversity of plants and critters, something most Garden Ranters now enthusiastically embrace in our gardens.

    My dubiousness comes from doubts that any bottled up Organic ACT Juice, or whatever they call it, costing many bucks a bottle will do a lick of good. It’s probably safe – but better be careful there, too. You’re right, Susan – in our culture, people start selling stuff so fast it is hard to tell marketing from legit research.

    And, too, I want gardening to be less gadget-y. Ingham’s devices cost hundreds of dollars and up, and homemade versions look like R2D2 trying to blow bubbles. It’s flirting with becoming a kind of outdoor hydroponics, where we try to control everything, seen and unseen, being and waiting to become.

    What about dancing in our veggie patch?

    What’s happening to good old gardening???

  8. The idea of compost tea sells because a) it sounds plausible and b) we’re kind of conditioned to feel like “hey, shouldn’t I be applying something 3-7 times a year?” Deciding to focus on boosting overall soil health and letting plants do their thing is a pretty major shift. I used to maintain the grounds for a non-profit, way back in the day before I really understood sustainability, and we were always doing something to that turf. When we bought our house, it felt kind of weird not to be spraying this and laying down bags of that.

  9. It’s completely about soil biology. Healthy soil should be teaming with billions of living organisms in every square inch. As we put chemical fertilzers in our soil, we hurt the organisms that are currently living there and making the nutrients that plants need. (native grasslands and forests thrive without man applying fertizlers). The microbes in compost tea drawn from fresh compost is literally a bunch of the living organisms from the compost being washed out and then introduced to the soil where they can start thriving on the organic matter in the soil. But these beneficial organisms like any living thing, need air, water, and food the continue to live. Compost tea that has been sitting in a bottle for days, weeks, and even months is filled with nothing but dead organisms so of course it will show little or no benefit. The USDA used to have a saying “feed the soil, not the plant” – that should still hold true. Healthy plants come from healthy soil which means let natures critters do their thing to transform dead organic matter into nutrients for the plants, and stop using chemical fertilzers – which kill off the soil biology. Let nature do the work and you won’t have to.

  10. 5 or so years ago, I was in charge of a Master Gardener experiment testing various growth promotion/disease prevention products on vegetables. We planted 5 beds with the same varieties of tomatoes, squash, pole beans, and some other things. Each bed contained the same mix of soil and really good compost. Each bed got a different foliar treatment, applied every 3 weeks. We tested 2 organic commercial fertilizers, ACT using a KIS-brand brewer and their compost “tea bags”, aspirin water, and a control bed that got only water spray. The compost tea failed miserably in terms of yield and disease prevention. In fact, the plants were stunted & more diseased than might be expected. I haven’t used the brewer since that season. The winner by a mile — 1 tablet of untreated aspirin, dissolved in 1/2 tsp vinegar, per gallon of water, plus a sticker like yucca extract. Unbelievable increases in yield and disease prevention. I also tried the ACT on my roses, hoping it would reduce blackspot. No such luck.

  11. One thing that is never discussed is the carbon footprint for making ACT. These brewers need aerating 24/7. That means electricity. How can people justify using such a product, when compost alone is already known to be a superior soil modifier?

  12. Thanks for this post Susan, and to Dr. Chalker-Scott for wading into the debate too. I’ve always thought that making compost tea was too laborious and labor-intensive. There’s no way I could possibly use it on my acerage, so I’m just glad to hear that it’s mostly a waste of time. Compost, yes, compost tea, too much bother, and why take the risk of using it on edibles?

  13. Thanks for the post.

    I’ve felt guilty for quite a while because while I do make compost, I don’t make compost tea. For the last two years all I’ve heard on the gardening programs is about the benefit of compost tea. I’m glad to know plain old compost appears just as good, if not better. Laura

  14. Perhaps the owner of the rose company has wonderful soil already filled with compost worms and a healthy dose of OM. This would make any placebo added to the mix seem worthwhile.

    I then would assume that singing to the roses would work wonder along with gnome manure.

    The TROLL

  15. As I read through this post, and through the subsequent comments, I have come to the realization that the discussion of Compost Tea (AACT) is akin to the health care debate. Both sides stay on there talking points, some of which are true, but neither side bothers to consider the whole truth about AACT.

    (My disclaimer: I am an organic lawn care provider, along with my landscape design business. I have learned, and do brew AACT from Dr. Elaine Ingham, and do believe it is a useful and powerful tool for organic land care.)

    The confusion regarding Compost Tea is understandable, and the many companies jumping into the market with wild claims of its efficacy is making things worse. The simple truth about compost tea is this; it is a very effective and powerful way to inoculate soils, leaf surfaces and even hydroponic systems, with the beneficial organisms of the soil foodweb, nothing more and nothing less. Furthermore these organisms, when introduced into these respective environments, can and will provide the plant with nutrients, and the ability to present a better defense against disease (this is simple plant biology). This is the same thing you are doing by adding compost, only compost tea speeds up the process.

    If one takes the time to look into the research of Dr. Ingham, they would find that her position is this; the best scenario is to provide the highest quality compost available to address soil health, made to the specification of the crop one wants to grow. In the event that there is not enough compost to adequately address the crop area, compost leachate, liquid compost extract, and Compost Tea can provide the numbers of organisms to make up for the lack of a sufficient amount of compost. As organic gardeners, we all know the benefits of right plant right place, but we should also now consider right organisms, right plant. And that is what brewing and using compost tea is all about, brewing the correct organisms for a particular crop, and introducing them to the crops environment.

    The risk of E. coli, is not to be ignored, knowing what is in one’s compost before brewing is important, and extensive testing is recommended to be sure pathogens are not being brewed.

    Brewing compost tea can be labor intensive for small properties, but not necessarily. When one has large or multiple properties to care for, AACT is definitely a cost effective tool to consider.

    Lastly, in our own experiences, we have seen tremendous results using compost tea on our clients lawns, but it is not a miracle nor a gimic, it is just science, biology to be precise.

    My hope is that we can move past the far flung claims, and the nay-sayers, and simply discuss what compost tea actually is, and what its benefits actually are.

    All the best,

    Scott Hokunson

  16. Scott, I beg to differ. It’s not a matter of “talking points”, it’s scientific data, or lack thereof. There’s been a similar debate on our Garden Professors blog, where another group of adherents to a particular belief system are relying on anecdotes rather than hard science. As Jeff Gillman and I said on our blog, you can believe whatever you like, and more power to you, but you can’t claim that compost tea use is based on science (and biology is a life science) unless there is hard evidence to support that viewpoint. (And I’m still curious how you can justify the use of electricity for manufacturing this product, rather than relying on nature to create her own “compost tea” as rainwater leaches through an organic mulch layer?)

  17. I’m a complete newbie to gardening compared to the others here but I just read in a couple different places that you could make your own organic fertilizer for free by rinsing out your milk, orange juice, yogurt, etc. containers, save up that gray water and pour it back into the soil.

    Wouldn’t that be the same idea and would it not only return nutrients but also microbes if your rinsing probiotic foods/liquids?

  18. Dr. Chalker-Scott, It is not my intent to belittle you, Mr. Gillman or others by calling your information ‘talking points’. I apologize if that is how it sounded.

    I am curious as to your comment that compost tea use is not based on hard science. I, and so far as I can tell those practitioners that use and promote the use of compost tea responsibly, are relying on hard science. We rely on plant biology, soil science, and microbiology to tell us what a plant needs to grow and survive. We then test to be sure that we are providing those essentials.

    We test the soil to ascertain the soil biology and what is missing for the crop to be grown. We then test the compost to be used for brewing, making sure the needed organisms are present and there are no pathogens. We then test the compost tea that has been brewed to be assured that the organisms have in fact been extracted and have multiplied. We then retest the soils the compost tea and additives have been added to, to be sure that the Compost Tea has in fact inoculated the soil. Now, as I’m sure you know, there are too many variables in this process to provide you with one set of data, and say that this process works everywhere. I would not ever make that statement, that is the reason we test each property.

    You are correct that nature will provide micro-nutrients and build soil micro-organisms, if left alone, but it simply cannot provide the numbers of organisms Compost Tea can in an equally short amount of time. Also, high quality compost is becoming harder to come by in large enough quantities to supply the growing demand of organic practitioners. This is another reason to consider Compost Tea. As companies continue to manufacture compost in larger and larger quantities to meet the growing demand, they will invariably leave a much (very much) larger carbon footprint with their large compost aeration tractors, than I do with my 1/2 hp 115v Sweetwater regenerative blower, that runs for 24-48 hours twice a month, 6 months out of the year.

    In the end, we are speaking of the same process, adding micro-nutrients and micro-organisms to the soil, using compost. ‘Any and All’ claims that Compost Tea is a magic elixir, or wonder product, should be ignored.

    With much respect,

    Scott Hokunson

  19. this is very similar to the alfalfa tea debate. for years i’ve been told by certain rosarians that to grow the biggest, healthiest roses, i had to go through the labor intensive process of making alfalfa tea. being the lazy gardener that i am, i opted instead for the easy way out by adding a layer of alfalfa pellets around the bushes. it worked great and breaks down to provide more compost to the soil.

  20. Scott, I appreciate the fact that you are, indeed, using scientific mthodologies in running soil tests, plating bacteria, etc. That’s not where scientists like Jeff Gillman and I have trouble. The problem is product efficacy: there are no credible scientific studies that repeatedly show any effect of applying these teas for disease control (or for any other reason, as far as I can tell from the literature). That’s what the researchers in the Rodale Institute study concluded. Ideally, you would be able to isolate strains of bacteria or fungi that compete with or kill pathogenic microbes, and spray these onto leaves. In fact, such microbes have been found – primarily in nonaerated compost tea made from spent mushroom compost. Until the compost tea science is advanced to the point where people can take a product, apply it, and get a consistent result, it simply can’t be regarded as a scientifically sound practice.

  21. I tried compost tea because 100’s of dollars of plants in my garden were dying. I had no idea what I was doing to make the tea. I made a cheap home kit with an aquarium bubbler. The plants were immediately changed from black to green, and produced fruit the next year (kiwis, cornus mas, many more). Making compost tea is a craft, not a science. There are way too many variables.
    For years I could kill bacterial diseases but not fungal. People started to tell me that I was filtering the fungal chains by filtering with socks. Bingo,after the change, now my quince and serviceberry have finally lost their rust. Someone trying to objectively replicate compost tea is like objectively replicating jazz music or cooking a great meal. The underlying scientific ideas about soil microbiology make sense based on other science experiments. However, just as laboratory experiments won’t produce a great meal that a French chef could, so won’t they be able to accurately test each one of the 35 steps that can change the tea and prove a yes or no. However, if you have diseases in your garden and you want a way to stop them without using toxic chemicals, aereated compost tea is a fantastic tool. You still have to prune, amend the soil, etc. also.
    John S
    PDX OR

  22. I just love this debate–so educational. I was talking with a group of gardeners on Key West yesterday and when I talked about those old gardners’ tales, those who used compost tea in a community garden were quite surprised. The Informed Gardener books are part of my show and tell. Thanks Linda!

    BTW, there was no snow in Key West…

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