What is Compost Tea & Leachate?
Compost tea, which includes vermicompost tea, is a nutrient-rich liquid created by
steeping finished compost or vermicompost in water. The compost infuses the water with
beneficial nutrients and is sometimes sprayed on foliage to reduce pests and disease or
used as a soil drench around plants to enrich the soil in the root zone. Leachate is
produced when water drains over compost. It is the liquid that is leached out of a
compost pile or worm bin. Since the liquid has possibly traveled through uncomposted
matter, leachate is not recommended for foliar application.
Why Make Tea or Use Leachate?
When created and used properly, many growers claim that compost tea and leachate
provide benefits for them and their plants. These benefits are summarized below:
• Improved plant growth and overall health
• Disease suppression
• Pest resistance
• Additional nutrients for plants and soil
• Less toxic chemicals and pesticides used
Given the high variability of compost materials used, production processes, application
methods, and the different environmental conditions for each batch of compost created, it
is hard to obtain scientific proof of the benefits claimed when using compost tea.
Basically, no two batches of compost are alike, so results vary. For any scientific
experiment, controls, replicated treatments, and repeated trials must be done to obtain
verifiable results. Therefore, many of the benefits are based on grower testimonials
rather than scientific evidence given the tendency for inconclusive scientific results.
Regardless of whether a gardener chooses to use compost tea or leachate, the ultimate
goal is to have healthy soils that produce healthy plants. A gardener’s first priority is to
build and sustain healthy soils by amending with quality compost.
Things to Consider:
Recent research brings up concerns about the presence of pathogens in compost tea.
When compost tea is used as a foliar (leaf) spray on food crops, pathogens may be
transmitted to humans. The following are some guidelines to follow when creating or
using leachate and/or compost tea in your garden to promote safe practices:
• Use potable water when diluting.
When using leachate:
• Use only as a soil drench. Given leachate may have been produced from
unfinished compost or vermicompost, it is not recommend for use in foliar
• Do not include any additives (molasses, kelp, fish byproducts, etc). These have
been found to increase the likelihood of pathogens.
• Use potable water when brewing or diluting.
When using compost tea:
• The safest use of compost tea is as a soil drench.
• Avoid additives (molasses, kelp, fish byproducts, etc.) when making compost tea,
as these can promote the growth of harmful organisms.
• If compost tea is being used as a foliar application on plants that are to be
ingested, it is recommended that it be used 3-4 months prior to harvesting.
• After the process is complete, sanitize equipment used.
To Aerate or Not to Aerate:
Aerating a tea means introducing oxygen into the mix by using a bubbler or method of
showering compost over a suspended tank. Some claim that aeration can speed up the
time it takes to produce finished tea and produces a more nutrient-rich product.
However, aeration does not eliminate the concern of pathogen presence as some have
previously believed. Results are inconclusive on whether or not aerated or non-aerated
teas are better for your plants and/or soil. Both methods require potable water, incubation
time, and filtration of the end product if it is to be used as a foliar application. Most users
recommend aerating tea for 24-36 hours, and letting non-aerated tea ferment for 5-8 days.
More research is needed to confirm the benefits and concerns related to using aerated or
Resources for Compost Tea information:
- April 6, 2004 National Organic Standards Board, Compost Tea Task Force Report http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5058470
- The Compost Tea Brewing Manual http://www.reboreda.es/Documentos/Manual,%20te%20de%20compos.%20Edition%203.pdf
- Compost Tea: Examining the Science Behind the Claims http://www.puyallup.wsu.edu/~linda%20chalker-scott/horticultural%20myths_files/Myths/magazine%20pdfs/CompostTea.pdf
- Recommendations for Safer Compost Tea http://www.ars.usda.gov/is/pr/2006/060921.htm
- Additives Boost Pathogens in Compost Tea http://www.ars.usda.gov/is/AR/archive/sep06/tea0906.htm
- USDA Study: Ecoli and Salmonella http://naldc.nal.usda.gov/download/18297/PDF
- Compost Tea Ingredients http://greenliving.nationalgeographic.com/compost-tea-ingredients-3004.html
- Additional concerns with Compost Teahttp://www.puyallup.wsu.edu/~linda%20chalker-scott/horticultural%20myths_files/Myths/Compost%20tea%20again.pdf