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
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.