More on Compost Tea

Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County

Client's Request (via phone):  What is the nutritional composition of compost tea?

Help Desk Response:  I am responding to provide you with some supplemental information relating to your phone discussion yesterday with my colleague from the UC Master Gardener Program Help Desk. I understand that you had phoned our Help Desk to ask whether we could give you some information about how you might determine the nutritional composition of your compost tea. As my colleague informed you, there are likely laboratories that perform testing of compost and compost tea, but our Help Desk does not have a list of such labs. If you decide that it might be worthwhile to do such testing after you review the information below, you might be able to find a testing lab by doing some Internet research. For example, you might want to do a search for “labs that test compost tea” which might bring up links to such testing labs.

Our research did turn up some information about compost tea that you might find of interest. Here's a link to a slide presentation on the “Nutrient Value of Compost” which appears to have been given at a symposium sponsored by the University of California in 2009: https://vric.ucdavis.edu/events/2009_osfm_symposium/UC%20Organic%20Symposium%20010609%2005b%20Hartz.pdf Slide 4 in the presentation shows typical nutrient levels of compost. As you'll see, the NPK (nitrogen-phosphorous-potassium)l nutrient levels vary depending on the source of the materials used to make the compost—for example, does the compost contain manures or only crop residues. Slide 17 in the same presentation notes that when the compost is diluted to make compost tea, the nutrient effect of using the tea is likely “insignificant”.

Another University of California source indicates that a potential benefit of compost tea is that the leaves of the plants may be able to directly absorb nutrients that are present in the tea for a quick nutrient boost. See:  https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=13471. However, as you'll see if you further review the information at this link, that same UC source is skeptical about the disease prevention claims that are sometimes made for compost teas. The authors eventually conclude: “Plain old compost, not the tea, typically acts to release those same nutrients in a slower manner, plus it has the added benefits of cooling and cushioning the soil. So to really get the most out of your compost, perhaps it's best to apply it to the landscape, and let nature make the tea with rain or irrigation water, unless you have a specific need for a quick, but problematic, boost of nutrients.

We hope that this information is useful as you evaluate your use of compost tea. You are welcome to contact us again if you have other gardening or pest questions. 

Help Desk of the UC Master Gardener Program ofCntra Costa County (TKL)

Editor's Note:  The editor has been following the use of compost tea for more than several years. While there is a lot of anecdotal enthusiasm for its use, conclusive scientific findings have yet to be made of its benefits. Prof Linda Chalker-Scott PhD of Washington State University has written extensively on compost tea. (click). If you are considering its use, the Editor recommends her various articles on its use.

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Note:  UC Master Gardeners Program of Contra Costa's Help Desk is available almost year-round to answer your gardening questions.  Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone:  (925) 608-6683, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog  (//ucanr.edu/blogs/CCMGBlog/)