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.)
Linda, how bout a link to your most complete article debunking compost tea?
I have a friend with a large and high end landscape business
and last fall I noticed his trucks on several properties I work spraying just about everything with this “magical” product. I’ve been meaning to tweak him about it and I’d like to include your article when I e-mail him to do so.
Linda, I thought you should include a link to this site to help the discussion. Thanks for your very useful work.
http://www.puyallup.wsu.edu/~Linda%20Chalker-Scott/Horticultural%20Myths_files/Myths/magazine%20pdfs/CompostTea.pdf
Alan, good idea – I modified the text to include that link. Thanks!
This is probably nit-picky, but I cringe every time someone uses “drink the Kool-Aid.” I’m cringing a lot lately. It trivializes I truly awful event. I don’t know if you are old enough to remember the photos of all those bloated bodies and the story of mothers feeding the poison to their children before drinking it themselves. I guess the distance of time makes it okay to use that phrase, but not for me.
Jan, I do remember that event and I’m not trying to trivialize it at all. For better or worse, the phrase has become part of the common vernacular and is a powerful way to describe someone’s willingness to accept something without question.
I think what happened to old fashioned compost is that anyone can make it with stuff they have at hand in his or her spare time. No one can make money from plain compost.
The biggest winners are the gardeners who make it and use it–less money spent & healthier plants.
Berkeley has to do something to keep their northern California cred. UC Santa Cruz is streets ahead of them with their Alan Chadwick Garden… it’s biodynamic!
Got cowhorns?
Gee, with such sterling examples set at our institutions of higher education, we wonder why people are becoming less scientifically literate. Thanks for this sad commentary, Matilija!
These days I’m seeing growers with large social media followings swear by compost tea in organic gardening. The claim I see a lot is that regular foliar applications of compost tea — usually in a mixture with emulsified fish, kelp, etc. — colonize the plant itself with communities of beneficial microorganisms, which out-compete pathogenic microorganisms, thereby replacing “chemical” pesticides along with fertilizers.
Which . . . um? Why would microorganisms which grew in a soup of most likely anaerobic, dark, decomposed plant material then happily colonize a rapidly-drying environment that is exposed to sunlight and open air?
I’m also remembering that agricultural liquid fish products are made using strong acid which is not always completely removed from the final product, and can burn leaves when applied to them in the wrong concentrations.
I admit, it is more satisfying to spray plants down with what you believe to be a magic potion than it is to shovel compost onto the bed. Good thing for me, our alkaline soils regularly require me to hit some of my shrubs up with foliar iron so I get my fix that way, with the added bonus of actually seeing quantifiable results that I don’t have to imagine!