California Department of Resources Recycling and Recovery (CalRecycle)

Organic Materials Management: Compost Tea

Compost Tea vs. Other Teas and Extracts

Compost teas can be made by farmers, landscapers, or home gardeners to enhance crop fertility and to inoculate the phyllosphere and rhizosphere with soluble nutrients, beneficial microbes, and the beneficial metabolites of microbes. Liquid organic amendments available are described below.

Compost Extract

Compost extract is a watery extract made from compost suspended in a barrel of water for no more than one hour before use, usually soaking in a burlap sack. The primary benefit of the extract will be a supply of soluble nutrients, which can be used as a liquid fertilizer. However, it will lack sufficient holding time for microoganisms to multiply and grow significantly.

Compost teas are distinguished from compost extracts both in method of production and in the way they are used. Compost teas are actively brewed with microbial food and catalyst sources added to the solution, and a sump pump bubbles and aerates the solution supplying plenty of much-needed oxygen. The aim of the brewing process is to extract beneficial microbes from the compost itself, followed by growing these populations of microbes during the 24- to 36-hour brew period. The compost provides the source of microbes, and the microbial food and catalyst amendments promote the growth and multiplication of microbes in the tea. Examples of microbial food sources are: molasses, kelp powder, and fish powder. Examples of microbial catalysts are: humic acid, yucca extract, and rock dust.

Compost Windrow Leachate

This is the dark-colored solution that leaches out of the bottom of the compost pile and collects on the ground, compost pad, or in collection ditches, puddles, and ponds and is often rich in soluble nutrients. However, in the early stage of composting, it may contain pathogens and would be viewed as a pollution source if allowed to run off site. Compost leachate needs further bioremediation and is not suitable or recommended as a foliar spray.

Building on the concept of compost teas as a liquid organic extract, what are some other common organic extracts used as a liquid drench or foliar spray?

Herbal Tea

These include plant-based extracts from plants such as stinging nettle, horse tail, comfrey, and clover. A common method is to stuff a barrel about three-quarters full of fresh green plant material, then top off the barrel with tepid water. The tea is allowed to ferment at ambient temperatures for 3 to 10 days. The finished product is strained, then diluted in proportions of 1:10 or 1:5 and used as a foliar spray or soil drench. Herbal teas provide a supply of soluble nutrients as well as bioactive plant compounds.

Manure Tea

Manure-based extracts are a soluble nutrient source made from raw, nondisinfected animal manure soaked in water. For all practical purposes, manure tea is prepared in the same way as the compost extracts described above. However, the manure is placed in a burlap sack and suspended in a barrel of water for 7 to 14 days. The primary benefit of the manure tea will be a supply of soluble nutrients which can be used as a liquid fertilizer.

Liquid Manures

These include mixtures of plant and animal byproducts, such as stinging nettle, comfrey, seaweed, fish wastes, fish meal, seeped as an extract. They do NOT include biosolids. Liquid manures are a blend of marine products (local fish wastes, seaweed extract, kelp meal) and locally harvested herbs that are soaked and fermented at ambient temperatures for 3 to 10 days. Liquid manures are prepared similarly to herbal tea—the material is fully immersed in the barrel during the fermenting period, then strained and diluted and used as a foliar spray or soil drench. Liquid manures supply soluble nutrients and bioactive compounds.

Caution: Manure teas are NOT the same thing as compost teas or compost extracts. Where raw animal manures are used as a compost windrow feedstock, the composting process—thermophilic heating to 135-160° F for 10-15 days—assures pathogen reduction. The raw organic matter initially present in the compost windrow undergoes a complete transformation, with humus as an end product. Any pathogens associated with raw manures will be gone. Because of concerns over pathogenic strains of E. coli, it is advised that growers reconsider manure teas and/or work with a microbial lab to ensure a safe, worthwhile product.

Compost Tea Home

Last updated: April 3, 2012
Organic Materials Management http://www.calrecycle.ca.gov/Organics/
Contacts: http://www.calrecycle.ca.gov/Organics/Contacts.htm