We set out to write a tidy little article about making compost tea, but found that this is not such a tidy little subject. Because of the many ingredients that can make good compost, the perfect recipe for compost tea is as varied as a recipe for the best chili.
Compost tea transfers the microbes, fine particles and soluble chemical components of compost directly to soil and foliage for quick results. You can make compost tea or buy it. You can also buy compost starters, additives and brewing devices for making tea from your own compost.
Or, instead of brewing, you can simply drop a shovel full of compost into a 5-gallon bucket of water and let it sit for a few days.
So, which one will you do, and is it really as straightforward as it seems?
What goes into it? Manure? Fish? Composted garden refuse? Does that mean plant disease too?
Brewing practices differ, especially in the intent to maintain a minimum level of oxygen in the brew, which is called an "aerated tea." Aeration is important to keep the good microbes in the tea alive. Other differences are in the dilution, added nutrients and the length of the brewing process.
One thing is for sure: Organic gardeners who practice tea brewing find the benefits of using compost tea on their plants—both in the soil and on the leaves—include increased growth, increased resistance to certain plant diseases and better yields.
On the other hand, the scientific community—who looks to set standards and replicate results—is concerned about compost tea safety, especially when the tea is enhanced with additives such as molasses that increase the good microbes and bad ones, such as E. coli.
In 2003 and 2004, a task force made up of farmers and scientists looked at the potential of compost tea contaminating edible plants with human pathogens.
The findings of the study show that you can make good compost tea from clean compost:
Use clean potable water, sterile equipment and clean compost. (Compost that reaches 131°F and stays there for at least three days should be free of pathogens.) Some gardeners also use vermicompost (from worms), which is supplied with some compost kits.
Watch your ingredients. The task force was very cautious about compost tea additives (molasses, brewer's yeast, kelp) because of their potential to encourage the regrowth of human pathogens and other harmful organisms.
Be sure to keep out rodents, flies and birds to help prevent contamination by harmful organisms.
Keep in mind that aerated teas are more effective than nonaerated. While you can purchase many brewing systems ranging from 5 to 500 gallons, you can make a simple one at home that includes a simple aquarium pump for aeration.
Serious tea makers can send samples for chemical and biological analysis. Tests, which begin at $24 each, require careful sampling and answers to a number of questions about the ingredients and process used. See www.soilfoodweb.com for information.
Compost Tea: Doing It Right
In 2003 and 2004 a task force comprised of farmers and scientists organized by the National Organic Standard Board (NOSB) reviewed relevant data to make recommendations on reasonable uses of compost teas. A major focus of their work addressed concerns about the potential of compost tea to contaminate edible plants with human pathogens. You can review their findings and recommendations in a PDF document available at www.ams.usda.gov
The Pennsylvania Department of Environmental Education offers easy step-by-step, illustrated instructions for making your own system that you can access online at www.dep.state.pa.us/dep/deputate/airwaste/wm/recycle/Tea/tea1.htm
Tea making techniques are continuously changing, as are findings about its results. If you like to curl on the sofa with old-fashioned reading called a book, try The Compost Tea Brewing Manual 5th Edition, by Dr. Elaine R. Ingham, Associate Research Professor in the Department of Forest Science at Oregon State University.
For a little lighter reading, a book that includes a chapter on compost tea making in addition to many other aspects of soil microbes, try Teaming With Microbes, A Gardener's Guide to the Soil Food Web by Jeff Lowelfels and Wayne Lewis (Timber Press; Portland, Oregon, 2006).