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Vermicompost tea (VCT)

Lorinda Balfanz, Mary H. Meyer and Carl Rosen

Compost and compost tea

Compost is a mixture of decaying organic matter, usually made from leaves, grass clippings, vegetable and fruit peels, manure and similar organic matter. Compost is used in gardening to improve soil structure, and in most cases provide nutrients. Compost tea (CT) is a liquid derived from soaking and or brewing compost in water and is used as a foliar and soil application to plants.

What is vermicompost tea and how does it work?

Vermicompost is compost that has been digested by worms (vermi). Vermicompost does not need to be turned, because worms "turn" the organic matter in their digestive tract, eliminating work for gardeners. Like compost, vermicompost is used to improve soil structure and provide nutrients for plant growth. Vermicompost tea (VCT) is a specific type of compost tea derived from soaking or brewing vermicompost in water.

VCT contains beneficial microbes that may also reduce or control diseases and improve soil health (Jack and Thies, 2006; Lowenfels, et al. 2006). Studies also indicate that VCT has a positive effect on suppressing tomato diseases (Zaller, 2006). Effects of VCT on turf are inconclusive, but studies indicate a decrease in certain turf diseases (such as microdochium patch) with regular applications of VCT (Conforti, et. al., 2002).

What nutrients can I expect in VCT?

VCT nutrients will vary based on the vermicompost source materials and the brewing techniques. VCT can contain the three basic plant nutrients: nitrogen in the form of nitrate or ammonium (N03 and NH4); phosphorus (P); and potassium (K). One analysis of VCT brewed at a 1:10 ratio showed on average: nitrate (NO3) at 77 ppm (parts per million) ; ammonium (NH4) at 3.7 ppm; P at 18 ppm; and K at 186 ppm (Balfanz, 2010). These are low amounts, and at least from this one study, VCT has been shown as a low source of nutrients.

How to make your own VCT

You can make or “brew” VCT yourself with minimal investment. Equipment needed is a large clean bucket, nylon material (such as nylon stockings) for holding the compost; vermicompost (or regular compost if you don't have access to vermicompost); a stick or dowel, an aquarium pump and water. The nylon material is necessary to submerge the vermicompost in the water, similar to a tea-bag. (The nylon keeps the vermicompost particles from leaching into the water which could clog sprayers or watering cans). An aquarium pump provides aeration as the tea is brewing. Aquarium pumps can be purchased at many pet stores (the size pump depends on the amount of tea you will be brewing) for 10 gallons use a Top Fin® XP-10 pump.

Steps to making VCT:

  1. Fill a bucket with tap water and let sit for 24 hours for the chlorine to evaporate.
  2. Place the aerator tip into the bucket of water and turn on the aerator for at least 2 hours before you add the compost. Aeration should take place before adding vermicompost to the water to increase oxygen levels in the water and reduce chlorine levels that are can be harmful to beneficial microbes. If the compost tea does not contain enough oxygen it will smell foul and can be harmful to plants.
  3. Measure vermicompost to achieve desired solid to water ratio. A good ratio is 1 part compost to 10 parts water. For example for a gallon of water (128 ounces), use 13 ounces of compost (about 1 ½ cups).
  4. Transfer measured vermicompost into nylon.
  5. Tie off nylon, so the vermicompost is submerged in water, but can easily be removed.
  6. Remove the aerator and place the stick or dowel over the top of the bucket and tie the nylon filled with vermicompost to the dowel so it will be suspended in the bucket of water (and be easier to remove when you're done brewing your vermicompost tea). Replace the aerator.
    Place the brewing VCT in a shaded area out of direct sunlight. Keep the VCT at temperatures between 60 and 80° F. A garage works well, since the tea will be away from sunlight, at an even temperature, and away from leaves and other debris that may fall into the tea.
  7. Write down the time/date you started brewing.
  8. After 48 hours of brewing, remove the vermicompost. (The water should have a yellow-brown color).
  9. Transfer the freshly brewed vermicompost tea into a watering can, sprayer, or other application device.
  10. Apply the vermicompost tea within 4 to 5 hours of brewing, otherwise the microbes will die and the tea will smell very foul.

Purchasing CT or VCT kits

For the non-do-it yourselfer, Compost Tea kits are available that can be purchased online or at gardening centers. Most kits include the following equipment: compost or vermicompost, bucket, aerator, material to strain the tea and instructions. You can also purchase brewing kits on-line; one example is Keep it Simple, Inc.

Applying CT or VCT to your garden

Compost tea is typically applied using a backpack sprayer or watering can. If using a backpack sprayer, the tea needs to be filtered (a coffee filter works well) before transferring it to the sprayer. When applying VCT, try to cover the plant completely. For soil drenches, the tea should be applied so that it reaches the plant's root zone. In general, applying 5 gallons of CT or VCT per 1,000 sq ft is a good rule of thumb. Since the nutrient value of compost tea is usually quite small, the rate may be increased depending on the plant's response.

Apply VCT early in the day, to allow the foliage to dry before night, which reduces the chance of foliar diseases. For disease suppression on fruits, vegetables and ornamentals, applications can be made as often as every 5 to ten days. For turf areas, weekly or bi-weekly applications may be needed for areas of high maintenance or if diseases are present. Because of unknown bacterial levels, it is not recommended to apply CT or VCT to fruits or vegetables.

VCT tips

The VCT should have a good earthy smell. If it smells foul do not use the tea since it may contain harmful bacteria that may damage plants (Lowenfels, et al. 2006).

Professional maintenance firms using VCT or any CT should have regular, at least annual, nutrient analysis of the tea prior to application in order to prevent potential plant damage. Nutrient testing is conducted at several universities - look on-line for one in your area.

Microbial content can also be analyzed. If you choose to purchase a VCT kit from a company they should provide regular microbial test results. If making tea yourself, you can have microbial analysis tests conducted through the professional laboratories such as soil food web or BBC laboratories.

Literature cited and other references

  1. Arancon, N.Q., C. A. Edwards, R. Dick and L. Dick. 2007. Vermicompost tea production and plant growth impacts. Biocycle. 48: 11, 51-52.
  2. Balfanz, Lorinda. 2010. Nutrient analysis of vermicompost tea and its effects on turf at the Minnesota Landscape Arboretum. Master of Agriculture final project. Department of Horticultural Science. University of Minnesota, St. Paul.
  3. Carballo, T., M. V. Gil, L.F. Calvo and A. Moran. 2009. The influence of aeration system, temperature and compost origin on the phytotoxicity of compost tea. Compost Science & Utilization. 17 (2): 127-135.
  4. Compost Tea Task Force Report. National Organic Standards Board. Accessed 21 May 2008.
  5. Conforti, C., M. Blair, K. Hutchins, and J. Koch. 2002. The effects of compost tea on golf course greens turf and soil: Presidio Golf Course, San Francisco, CA.
  6. Jack, A.L.H. and J.E. Thies. 2006. Compost and vermicompost as amendments promoting soil health, in Biological Approaches to Sustainable Soil Systems, N.T. Uphoff, Editor. CRC Press: Boca Raton, FL. p. 453-466.
  7. Lowenfels, Jeff and W. Lewis. 2006. Teaming with microbes: A gardener's guide to the soil food web, Timber Press, Inc. Portland, OR.
  8. Scheuerell, Steve. 2003. Understanding how compost tea can control disease. Biocycle. 44(2): 20-25.
  9. Sherman, R. 2010. Vermicomposting in North Carolina. North Carolina State University. Accessed 15 December 2010.
  10. Zaller, J.G. 2006. Foliar spraying of vermicompost extracts: Effects on fruit quality and indications of late-blight suppression of field-grown tomatoes. Biological Agriculture and Horticulture. 24: 165-180.
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