Worm Compost Tea & Leachate

You may not be aware but there are numerous benefits of using worm tea in your soil. If you are a gardening enthusiast, you can use worm tea to replenish the soil with nutrients and protect plants from many plant diseases.

Worm tea has the same benefits as worm castings, but in liquid form. Castings are produced when worms break down the organic matter in the soil. It is also called “worm manure” or “worm humus.” These castings are present in the worm beds. When you run water through these castings, nutrients such as nitrogen, calcium, and magnesium are picked up. The process of harvesting worm castings is called “vermicomposting.”

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.

How to Make Worm Tea
For making worm tea, you will need a large bin or worm compost bin, such as the Wiggly Wranch bin. The bottom tray should have a drainage spout and holes for aeration. Soak a handful of worm castings in at least 5 liters of warm water.Allow the castings to soak for a couple of days. Next add a teaspoon of molasses (optional). Molasses will promote the growth of micro-organisms. If you feed your worms a balanced diet such as fruits and vegetables (no meat or dairy) they will produce the best castings and worm tea. The water must be chlorine free because chlorine will destroy the “good” bacteria. To help conserve water, rain water is a good source of unchlorinated water to use. Pete Ash, an experienced gardener, long time master composter, and organic farming and gardening teacher, crafts a tea bag of the compost and vermicompost to soak in water. He suggests using an aquarium pump to keep the water aerated to stimulate micro-organism growth. Pete says, “The idea is to wash the microbes out of the compost into the water; adding a simple starch or sugar to the brew to feed the bacteria that are breeding. Use the wash water from rice rather then washing it down the drain.”

How to Use Worm Tea
The best way to use worm tea is to dilute it. Pete owns a few Wriggly Wranch bins. He dilutes the worm tea with 4 to 6 parts water (or more) for foliar spray applications. He also recommends using the tea within a couple of days and as it accumulates it may spoil. It is not clear to anyone how long worm tea should brew for, but if it smells bad you should not use it. Pete harvests his castings regularly because the mucus can build up along with bacteria and can actually become toxic for the worms. As Pete says, “No one likes to live in their own feces.”

Benefits of Worm Tea
Worm tea and compost is excellent for a garden. Pete uses worm tea as a foliar spray and compost tea as a field spray. There are many, many uses for worm tea. Here are a few ways to use worm tea to grow healthy fruits and vegetables:

  • Use worm tea as an inoculant for potting soil. The nutrients in worm tea help seedlings grow strong. It is suggested that inoculation should be done two weeks before you plant your seedling.
  • Worm tea also helps recover polluted soil. If you repeat the worm tea applications, the microbes will convert and metabolize organic and inorganic chemicals. The worm tea will help sequester the heavy metals found in chemicals.
  • Sometimes lawns can become sterile due to chemical treatment. Worm tea will repopulate the soil with microbes, enrich the roots and break down the thatch turning it into food for grass.
  • During hot summer days, worm tea can help retain water in soil.
  • If you decide to use worm tea as a foliar spray, it will help your plants produce more foliage and larger stems. This greatly helps plants that are lacking enough sun.
  • You may also add worm tea to a compost pile to speed-up the break-down process.

By using worm tea, you can help the environment by reducing and even eliminating the use of chemical fertilizers that can cause water pollution. Studies show an average American family produces a ton of waste each year. The estimate is 1/3 or ½ of household waste is organic matter (kitchen waste). If you vermicompost, you will reduce the amount of organic matter that ends up in landfills, help mitigate global warming and make nitrogen-rich organic fertilizer and worm tea for yourself. Vermicomposting is nature’s way of completing the recycling loop. If you are interested in learning about “the circle of life…the circle of rot” please refer to our March 2003 newsletter for a discussion of why you should compost, how this is improves healthy soil, which in turn creates healthy vibrant plant life.

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 applications.
  • 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 non-aerated teas. 

Resources for Compost Tea information: