Horticulturists, scientists, teachers, gardeners, practioners and farmers all rave about compost and the benefits to the soil, like improving soil structure, reducing water use, improving aeration, attracting earth worms and many more. I want to believe the same thing holds true for compost tea, is it the cure all for damping off disease, will it make my tomatoes “luminescent”(6), will it make my lawn greener, will my plants have less disease and eliminate pest problems, will it make my soil a better place for my plants, the claims for compost tea are numerous, does it really work?
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Compost tea has been around for thousands of years perhaps as far back as the Roman Empire (6). “Somebody noticed that plants grew better around manure or on manured ground. But solid manure was hard to work with. So it went into a container of water to let it steep for awhile and we can be sure that it got stirred. When used as a drench, plant growth improved. In the late 1990’s aeration was first introduced into the compost tea.”(4) Aeration claims to increase beneficial microbes and “accelerate the process by creating optimum levels of oxygen for growth and reproduction of beneficial aerobic microorganisms.” So there are now numerous definitions of compost tea.
Compost leachate which is the runoff of water from compost or worm bins. The material is a brown colored water that runs out of compost or worm bins when the bins or piles become too wet. The liquid is a product of compost or worm casting that has not completely finished the compost process. “Most likely rich in soluble nutrients; but in the early stage of composting it may also contain pathogens”(11)
Compost extract is what was originally called compost tea. Compost is wrapped in coarse fabric and soaked in water for days. “The primary benefit of the extract will be a supply of soluble nutrients, which can be used as a liquid fertilizer”(11)
Compost tea is an aerated mixture of compost and food sources for microbes; such as kelp, molasses, fish hydrolysates, rock dust and humic acids. “The compost-tea brewing technique and aerobic process extracts and grows populations of beneficial microorganisms.” (11)
Compost tea can be added to soil to improve soil life and impacts plants more quickly than a composted mixture. (7)
The reasoning behind compost tea is that once the mixture has completed and is applied as a soil drench it will add microbes to soils which in turn help to break down organic material in the soil and can then be used for food for plants. And the need for synthetic fertilizers becomes less. There are many different recipes for compost tea based on your needs, there are fungal teas which are good for acid loving plants and trees and shrubs, there is some evidence that beneficial fungus will help with some diseases like powdery mildew and downy mildew. And there are bacterial teas which are good for vegetables, annuals, perennials and grasses.
What is compost tea? The soil food web defines compost tea as: “essentially, is a brewing process that extracts microorganisms from compost followed by microbial growth and multiplication. This includes beneficial bacteria, fungi, protozoa, and nematodes. When compost teas are sprayed onto the leaf surface, these beneficial organisms occupy spatial niches on the leaf surface and gobble up leaf exudates that pathogenic organisms would otherwise feed on to prosper; other microbes directly interfere with pathogenic organisms through antagonism. A more simple definition: Compost tea, in modern terminology, is a compost extract brewed with a microbial food source-molasses, kelp, rock dust, humic-fulvic acids. The compost-tea brewing technique, an aerobic process, extracts and grows populations of beneficial microorganisms” (11) based on the ingredients that you use you will either have bacterial tea, fungal tea or a combination
“Compost Tea has been field tested to be effective in suppression of the following diseases: black spot, mildew (downy), needle cast on pine, vertilcillium wilt, white flies, mealy bugs, rust, aphids, tent caterpillars, mites, leaf curl, red thread (early and late), fungal diseases in ornamental cherries” per the website http://www.simplici-tea.com/disease_suppression.htm. However, I have not found any science based information to back this claim.
What about the science?
A trial at the University of Oregon conducted on black spot on roses showed “Roses in locations with shade suffered from powdery mildew. Compost tea did not seem to affect powdery mildew. One private location observed that the roses sprayed with tea at that location seemed healthier overall than those that were not sprayed. They had glossier leaves and more blooms overall. Two of the three test groups in 2007 showed a slight improvement in incidence of disease over plants that were not sprayed. The difference was not statistically greater. The average between 2006 and 2007 still showed control group doing better than the experimental group.” (8)
“In comparing the matched pairs of eight Prunus spp., the compost tea extract was not significantly different from the water application for any of the eight cultivars tested. In fact, for some trees it made the problem worse. “(9)
An excerpt from a study on aerated compost tea to suppress dampening off disease “While further work is needed to directly quantify the residual sucrose concentrations in aerated compost tea produced with molasses-based additive to determine the effect on damping-off suppression, there are strong indications that the use of simple sugars as additives should be avoided when producing compost tea for disease suppression. In addition to the potential of residual nutrients increasing Pythium damping-off, the use of simple sugars in producing compost tea has been linked to growth of E. coli in aerated compost tea makers when compost contaminated with E. coli was used.” (1)
“Turf quality ratings initially were very low for the tea drenches, therefore it was decided to apply liquid fertilizer over the tea treated plots to maintain acceptable turf quality. This addition masked any further differences in turf quality. The foliar tea applications suppressed dollar spot 40 to 60 percent when compared to untreated plots in one of three years. It is unlikely that due to the variability of brewing results, little microbial benefit, and the labor required for brewing tea that this technology will see widespread adoption in its current form.” (2) However a trial at Harvard University (Prepared by Harvard Facilities Operations Maintenance) which used a combination of compost tea, compost and organic fertilizer,” increased the depth of turf roots, decreased water usage, and increased available nitrogen,” since they were using a combination of organic methods there is no definite proof that the compost tea was a main contributor. When asked if they had done any studies on compost tea, they said “We only use compost tea as a portion of our organic program so unfortunately we have not done any studies on compost tea alone.”
Dr Linda Chalker-Scott PH.D. WSU states that “clearly the science is not strong for aerated tea use on crop plants, much less on lawns, shrubs and trees.” (3)
After twelve weeks of compost tea treatment, there are evident responses among the microbial community, however, it’s too early to draw conclusions about the efficacy of the compost tea treatment. (5)
“The production and application of compost tea is primarily focused on: disease suppression, supplementing plant nutrients, and increasing soil microbiology to improve soil structure, water percolation/retention, rooting depth and consequently improved plant growth. The research conducted worldwide on compost tea is scarce and the results are highly variable. Results vary from suppression of some diseases to no effect in disease suppression at all, or in few cases increased incidence of diseases. Where compost teas are compared with conventional fungicides, in most instances compost teas have been relatively ineffective. Compost tea producers estimate that up to 5,000 farms are using compost tea in New South Wales, Australia these are mainly organic farms. Use of compost teas is based on faith or anecdotal evidence rather than based on replicated scientific research at this stage. Researchers acknowledge that there are significant limitations in our knowledge of compost teas and its use, and hope that an increased understanding of compost tea microbiology and the survival and interactions of microbes on plants surfaces will enable compost tea production practices and application technology that optimizes disease suppression.” (15)
Lee Reich PhD in horticulture wrote in “Fine Gardening Magazine” January 2007 an article titled “The Jury is Still Out on Compost Tea” where he says “Benefits from compost teas are on even shakier ground when the tea is used to improve the soil. Compost has been shown to improve soil tilth, help soil retain nutrients, enhance nutrient availability, increase rooting depth, and suppress root diseases. Compost tea, by extension, is credited with providing these same benefits. Therein lies part of the great appeal of compost tea. Who wouldn’t rather improve an acre of soil with the recommended 15 to 20 gallons of compost tea rather than have to heave around 2 to 5 tons per acre of compost? But compost and compost tea are not the same. They differ quantitatively and qualitatively in microbial makeup, and most dramatically, one is a relatively small volume of liquid and the other is a relatively large, mostly solid mass. Compost’s bulk comes mainly from carbon compounds, which are the major foods for beneficial microorganisms. Compost tea contains relatively little of these carbon foods. The beneficial microorganisms of composts and compost teas are already present in most soils and will multiply rapidly if food supplies permit. If your soil does not have beneficial microorganisms, it probably means the conditions aren’t hospitable to them. Unless you improve those conditions, any added microorganisms will die.” This article provided a lot of discussion on the internet when it was first published and now includes a new string of posts on http://www.redwormcomposting.com/worm-tea/is-compost-tea-just-a-fad/ dated January 13th 2011 since that date there have been fifty eight posts. Most of the posts favor the use of compost tea and the major opinion is no compost tea mix is the same and if it works for you continue to use it.
“If you have good soil conditions and your plants are healthy there may be no reason for compost tea. But if you have a small amount of compost and need a vast improved soil, when plants are struggling, showing signs of stress or when you want to apply composts benefits to a lawn these might be good reasons to use compost tea” (Plesand).
With so many claims about compost tea,” in 2003, the National Organic Standards Board convened a Compost Tea Task Force to review the relevant scientific data and report their recommendations on compost tea. The Task Force was composed of 13 individuals with knowledge and expertise in organic farming practices, organic certification, EPA pathogen regulations, compost, compost tea production and analysis, plant pathology, food safety and environmental microbiology.” The final report can be found at http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5057213. They came back with ten steps to be used in making compost tea, found a lot of practioners that use compost tea and also established there was not a lot of science based evidence behind the use the compost tea, and a possibility of contaminating crops.
In conclusion there could be benefits from compost tea but there have not been a lot of scientific studies on the use as prevention for diseases and pests or that it increases dramatically the growth of plants. Compost tea has a lot of different variables by the type of compost used; vermicompost, manure compost, leaf and grass clipping compost, and any other possible compost mix. Another variable would be the additives to the tea molasses, kelp, humic acid, granite dust, fish hydrolysates, fungal foods like oatmeal and powdered baby oatmeal. And then there is the time and temperature of mixing with aeration. There appears to be some advantage of using compost tea but a lot more studies need to be done to prove the claims of the some websites and even some famously written books.
The question has been asked why not more research on compost tea? “Compost teas are highly variable in their microbial and nutrient content from batch to batch. This translates to high variation within data sets and often leads to inconclusive results. Unfortunately, these results are often not published even though they are just as important as positive outcomes. In other words, if a particular treatment doesn’t work well under controlled experimental conditions, it’s unlikely to work consistently anywhere else.”(18)
With that being said, there is no harm in trying to make your own compost tea and doing your own experimentation. There has been some back and forth discussion on the use of molasses and e coli in compost tea, so if one uses molasses read the scientific data before applying to edible plants. Per Dr. Linda Chalker-Scott, PhD “While the scientific evidence is certainly lacking for Aerated Compost Tea activity in disease control, there is a serious, documented concern with these types of compost teas,” says Dr. William R. Schneider, a research scientist in the Biopesticides & Pollution Prevention Division (Office of Pesticide Programs) of the USEPA. He continues “it is very difficult to do a microbial pesticide risk assessment on a mixture of unidentified microorganisms that could easily contain human and nontarget organism pathogens.” Indeed, this risk is significant in ACTs that have been “enhanced” with molasses, kelp, and other high-nutrient additives. Such ACTs have been documented through scientific research to contain E. coli and Salmonella populations, both of which are human pathogens. The recent deaths due to E. coli-contaminated spinach illustrate how dangerous compost tea applications can be, particularly on food crops. Even though there have not been any reports of problems from compost tea make sure you read all the reports.
“The use of compost tea as part of an integrated plant health management strategy will require much additional whole systems research by a cohesive team of farmers and experts in composting, plant pathology, phyllosphere biology, molecular microbial ecology, fermentation science, plant physiology, plant breeding, soil science, and horticulture.” From the Organic Agriculture Centre of Canada posted April 2010 (13)
A controversial name in compost tea is Dr Elaine Ingham with Soil Foodweb who has published “The Field Guide I for Actively Aerated Compost Tea”, “Compost Tea Manual 5th ed.” and a number of other books, CDs and offers seminars on compost tea. She has done a lot of research on soils, and helps farmers all over improve their soils; but has not published a lot of peer reviewed research on compost tea. In January 2011 the Rodale Institute “a non-profit dedicated to pioneering organic farming through research and outreach” named her Chief Scientist; and will be in charge of research at the institute, hopefully now, there will be more research on the benefits of compost tea.
“So despite all the hype, compost tea is not the silver bullet everyone is looking for. Unfortunately, nature is not that simplistic. But it’s fun to experiment. (I do lots!) If you do experiment, and come up with a formula that you think works-try replicating it in a scientific way” (16) per the Whatcom County Master Composter Recycler Program.
How do I make compost tea? “The USDA suggests using a sump pump to bubble air into the extract for 24-36 hours” (Sac Bee). First you need a brewer you can purchase a brewers which makes 500 gallons for around $11,647.00 to $50.00 for a 5 gallon brewer. And then purchase packaged mixes and just add water. You can also buy brewers and make your own mixture, using your own compost or vermicompost. Another option would be to make your own brewer using a five gallon bucket, an inexpensive aquarium pump, an air stone, some aquarium tubing and a porous bag of some type. There are numerous directions on the internet. Once you have a brewer to make the tea; there are numerous recipes on the internet. “One simple recipe is five gallons of chlorine free water, six cups of compost or vermicompost, three tablespoons unsulfured black strap molasses. Cover the container Brew this for twenty four to forty eight hours at 75â° let rest ten minutes and then use immediately.”(Remillard) The compost tea should smell good (earthy) and have a brownish tea color. If the tea smells bad it has gone anaerobic it could contain ammonia and dangerous bacteria and should not be used. Once the tea is made it can be diluted one to three, one to two or used full strength. It can be used as a soil drench on a wet soil any time of the day. It can be used as a foliar spray in the early morning or evening. If you are using a foliar spray it would be a good idea to filter the tea first so you do not clog your sprayer. When making compost tea make sure you start with good smelling compost or vermicompost the better the compost the better the tea.
Another easy recipe for compost tea Home-size compost tea recipe comes from W.F. Brinton at Woods End Laboratories Inc., Maine.
1) Use well-aged compost, at least 4 months old. 2) Put in a large pail or barrel outdoors between 59â° and 68â°C. 3) Add water, 1 part compost to 5 to 8 parts water
(i.e. 1 cup of compost to 5 cups of water). 4) Stir daily for five days. The strong smell should slowly dissipate. 5) On the fifth day, pour through a sieve or a cheese cloth. 6) Spray on plants in periods of disease outbreak, or drench the soil at the base of the plant. 7) Do not spray edible plant parts to be harvested in the following 2 to 3 weeks.”
CalRecycle (a CA.gov website) on their website says “But why go to all the trouble of “brewing” and spraying this tea instead of just working the compost into the soil? Two reasons: To inoculate microbial life into the soil to feed the foliage of plants, and to add soluble nutrients to the foliage or soil in order to feed your plants. Compost tea is a readily available form of compost that will impact the plant more quickly than compost mixed into the soil.” I am not sure how they came up with this information as no scientific evidence has been found that all this is true.
When it comes to state Master Gardener programs there is also a lot of different opinions.
The state of Pennsylvania tells you how to make compost tea at http://www.dep.state.pa.us/dep/deputate/airwaste/wm/recycle/tea/tea1. Arizona state university extension tells you how to make compost tea at http://ag.arizona.edu/yavapai/anr/hort/byg/archive/composttea.html. However, Washington state master gardeners cannot recommend compost tea. “Because Washington State University Master Gardeners are volunteer educators who rely on science-based information, they cannot recommend a practice or product that lacks a legitimate scientific basis. Furthermore, it is illegal to sell unregistered substances for use as pesticides. There are no compost tea products registered as pesticides within the U.S. Environmental Protection Agency. Neither WSU Master Gardener volunteers nor Web sites may encourage the use of compost tea as a pesticide. (9) Then Oregon State University extension tells you how to make compost tea on their website and their Master Gardeners sell compost tea as a fund raiser. In California per Pam Geisel Statewide University of California Master Gardener Coordinator “We don’t recommend compost tea because we do not have science based information on it at this time. Also, compost tea is so variable in terms of content that making a generalized recommendation would be impossible as to the quality and the plant response.” “Organic Gardening senior editor says “he is convinced that ‘There is the potential for a health hazard’ from its use (compost tea) – 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.”
Finally, I think the Extension Horticulture Agent, in Anchorage Alaska, Julie Riley sums it up best, “Compost tea is like a religion-you have to have faith. I know there are Anchorage Master Gardeners who feel they get good results with compost tea. I’ve always said to gardeners ‘if you are happy with your results, keep doing what you are doing'”
Bibliography and Citations
(1) Scheuerell Steven J. and. Mahaffee Walter F First author: Department of Botany and Plant Pathology, Oregon State University; and second author: U.S. Department of Agriculture- Agriculture Research Service-Horticulture Crops Research Laboratory, Corvallis, OR 97330. “Compost Tea as a Container Medium Drench for Suppressing Seedling Damping-Off Caused by Pythium ultimum” Accepted for publication 14 June 2004. Web March 2011.
(2) Rossi Frank, Cornell University, Cornell University, 134a Plant Science Bldg., Ithaca, NY 14853 “Effects of Compost Tea on Turfgrass Performance, Disease Incidence, and Soil Microbial Populations.” Nov. 8, 2007 Web March 2011.
(3) Chalker-Scott, PhD. Linda, Extension Horticulturist and Associate Professor, Puyallup Research and Extension Center, Washington State University www.MasterGardenerOnline.com • MASTERGARDENER winter 2007 pages 8-10, Web March 2011
(4) Moore, Robert C; “History of Compost Tea” thesoilguy.com N.p, n.d web March 2011
(5) Stevenson, Emily; Yale School of Forestry, Alexander Felson and Mark Bradford Environmental Studies Advisors, “Closing the Loop: Alternative Land Management at Yale, Hixon Fellowship 2010, web April 2011
(6) Remillard Marc, Compost Tea Making, Ascension Press, April 2010
(7) Author unknown, “What Is Compost Tea, and Why Use It?” CA.Gov CalRecycle, California Department of Resources Recycling and Recovery, March 24, 2005, web April 2011
(8)Wise, Cindy, “Compost Specialist Compost Tea Trial 2007, OSU/Lane County Extension Service Compost Specialist tea trial, December 2007, web April 2011
(9) Chalker-Scott, Linda Ph.D., Extension Horticulturist and Associate Professor,
Puyallup Research and Extension Center, Washington State University “The Myth of Compost Tea Revisited: “Aerobically-brewed compost tea suppresses disease”, April 2001, Web May 2011
(10) Lanther, Mario, “Compost Tea and Its impact On Plant Diseases”, BC Organic Grower, Volume10, Number 2, spring 2007, Web April 2011
(11) Diver, Steve, NCAT Agriculture Specialist “Notes on Compost Teas” The National Sustainable Agriculture Information Service – ATTRA – 2002 Web March 2011
Ingham, Dr Elaine, Rollins, Carole Ann ed., Sustainable Studies Inc. and Natural Technologies, The Field Guide 1 for Actively Aerated compost Tea (AACT) April 2001-June 2003 Second Edition, Second Printing March 2007
Pleasant, Barbara and Martin, Deborah; The Complete Composting Guide, Storey Publishing, LLC February 13, 2008
Arrington, Debbie, “Now there’s distinction between compost ‘tea,’ ‘extract'”, Sacramento Bee, Saturday, February 26, 2011, page D5.
Geisel, Pam, Personal interview May 10, 2011
(12) Harvard Facilities Operations Maintenance, Harvard Yard Soils Restoration Project, 2009 President and Fellows of Harvard College, February 2009, Web March 2011
(13) Scheuerell S. and Mahaffee W., “Compost tea: Principles and prospects for plant disease control” Organic Agriculture Centre of Canada, April 2010, Web March 2011
(14) “Aerated Compost Tea” Oregon State University Extension Service Douglas County, November 14, 2009, Web April 2011
Chalker-Scott, Dr. Linda PhD Associate Professor and Extension Urban Horticulturist
WSU Puyallup Research and Extension, “Compost Tea: Examining the science behind the claims” N.d., Web April 2011
(15) Overview of Compost Tea Use in New South Wales. Recycled Organics Unit (2006). Recycled Organics Unit, internet publication: 2007 second edition, Web March 2011
(16) “To Tea or Not to Tea” Whatcom County Master Composter Recycler Program, Bellingham, WA, N.d. Web May 2011
(17) Harris, Susan, “Still confused about compost tea, I turn to Rodale” Garden Rant, Uprooting the Gardening World, February 25, 2010, Web May 2011.
(18) Reeves, Walter, The Georgia Gardener, “Compost Tea – Does it Work?” N.d, web May 2011
Martin, Deborah L. and Gershuny, Grace, Ed., The Rodale Book of Composting, Rodale Press, 1992
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