Building good soil with compost tea

"Feed the soil, not the plant" has long been my mantra. A thriving soil full of organic matter and alive with microbes, worms and other living things provides a plant all the nutrients it needs.

Traditionally, one way to build a good soil was to make a non-aerated compost tea and pour the brew on the soil. This traditional method was a passive process producing a mixture containing anaerobic (no air) microbes and nutrients. Now compost tea brewers can be purchased or made at home to aerate a mix that contains aerobic microbes and nutrients. Why does this matter?

First, what is compost tea? Dr. Linda Chalker-Scott with Washington State University Extension wrote an article in MasterGardenerOnline.com (winter 2007) titled "Compost Tea: Examining the Science behind the Claims." She describes traditional compost tea as the soaking of animal manures and plant wastes in water until the water turns black. The juice was then applied around plants.

In reference to the aerated products, Chalker-Scott points to research by the Environmental Protection Agency that states "there is serious documented concern with those types (aerated) of compost teas." When animal waste is augmented with high nutrient additives such as molasses or kelp and then air is added, they have been documented to contain E. coli and Salmonella. These are both human disease organisms. We all remember the E. coli contaminated spinach deaths. Aerated compost teas can be hazardous to human health on food crops.

The National Organic Standards Board (November 2006) carefully lays out the rules for organic producers on how to properly compost so that they manage raw manures in order to prevent contamination. They define compost tea as a "water extract of compost produced to transfer microbial biomass, fine particulate organic matter, and soluble chemical components into an aqueous phase, intending to maintain or increase the living, beneficial microorganisms extracted from the compost." They require that it be made from potable water, in sanitized equipment with compost that meets their standards (heated to a temperature of at least 131 degrees for a minimum of three days.) If compost tea is made without compost tea additives, it can be applied without restriction. If additives were used, the tea must meet EPA recommended recreational water quality guidelines for fecal contamination, E. coli and others.

Even though a non-aerated compost tea may be safe, Chalker-Scott recommends gardeners simply make compost and use it as a mulch layer rather than make compost tea.

JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension and may be reached at skellyj@unce.unr.edu