Compost Tea

What is soil?

The three basic soil types are sand, clay, and loam. The first two are not usually desirable, either because they do not retain water or are too easily compacted and prevent root growth. Loam is the happy medium, containing approximately even portions of sand and clay. While an even ratio of sand and clay will provide the ideal structure for a plant to grow, it does not give any nutrient to feed the plant.

One of the key tenets of organic agriculture is the nurture and development of the soil. In stark contrast to conventional agriculture, which treats the soil as simply a substrate to hold plants in place (key nutrients are applied through chemical fertilizers), organic practices treat the soil as the “mother crop” from which all others spring forth. In addition to crop rotation and mulching, the use of compost is essential in providing plants with the nutrients they need to grow. The essential components of compost are fungal and microbial life which break down organic material and deliver vital nitrogen, phosphorus, potassium, and other nutrients to plants.

It’s no secret that while compost is great for the soil, it can difficult to work with. Compost tea can be equally difficult to work with. The advantage we find is the amount of acreage we can cover with tea as opposed to compost. Enter aerated compost tea. Aerated compost tea is an effective way to treat a large or small area of soil with a dense concentration of nutrients, minerals, and soil-nurturing fungi, bacteria, nematodes, and protozoa. If you have access to an inexpensive microscope, you can see the results of your efforts. Turn the brewing of compost tea into a fun science experiment!

Brewing Compost Tea: An Overview

Compost and worm castings are placed in a “tea bag” which is soaked in a solution of water and minerals. Bubblers aerate the water to keep the aerobic microbes active. Over a period of 24 to 48 hours, bacteria will multiply and fungal strands will grow, and the nutrients in the worm castings and compost will be suspended in the water. The resulting tea can be applied as needed with a variety of different methods with hand and bucket or a liquid spray pump being the most common. Compost tea can be mixed with hay as an additional pasture remediation technique. Anywhere from 25 to 100 gallons may be applied per acre for best results.


There are eight ingredients that we use to brew compost tea for our pastures at Coyote Creek Organic Farm.

  1. Compost – well composted organic material from a thriving compost pile works best. Remember that we need a supply of microbes, fungi, and protozoa to start with.

  2. Worm castings – the richest natural source of fertilizer!

  3. Trace Minerals – there are 14 essential minerals for plant growth including zinc, copper, manganese, and iron

  4. Green Sand – a natural, slow release fertilizer from ocean deposits

  5. Humic Acid – increases the effectiveness of fertilizers

  6. Molasses – helps to feed microbial life in the compost tea

  7. Kelp – contains trace minerals and naturally occurring hormones which stimulate root growth

  8. Water

Brewing Equipment

The method for brewing compost tea is easily scaled up or down. At Coyote Creek Organic Farm, we have around 70 acres cycling in and out of production. For our farm, we brew tea in 200 gallon batches. As we move our henhouses and pens around the pasture, we follow up with an application of compost tea to the areas most recently occupied by the chicken houses. You will need to assess your own requirements and build your compost tea brewer to fit your needs. Our system uses the following:

  • 1 – 250-gallon IBC tote bin

  • 1 – 4” diameter PVC pipe with cutouts and mesh covering

  • 1 – “Tea bag”

  • 1 – screen, through which small compost particles and compost constituents flow

  • 3 – ½ horsepower pond aerators (bubblers) with hoses

  • 3 – 1” PVC pipes approximately 4’ long

  • 3 – PVC pipe end caps drilled with ⅛” holes

  • 3 – Metal rods approximately 2 feet long

  • 1 – Microscope with minimum 100x magnification

Brewing Recipe

The specific brewing recipe will vary depending on ambient temperature and cloud cover. When temperatures are above 78 degrees Fahrenheit and sunlight is direct, less than 1-cup of molasses is to be used, and brewing times may be shortened based on microscope testing.

  1. Prepare the 250-gallon IBC tote bin by canting it towards one corner by placing 2×4’s under three corners of the tote bin. Make sure the bin is stable and secure before proceeding. Angling the tote will encourage the water to flow freely throughout the tote when the bubblers are used.

  2. Mix 10 pounds of compost and worm castings at four parts compost to one part worm castings.

  3. Begin filling the IBC tote with water. Once an estimated 25 gallons of water has been added, add humic acid. Follow the supplier’s instructions to ensure correct humic acid concentration.

  4. Insert “tea bag” into its proper place inside the tote bin. Insert the bubbler into the bag and turn it on.

  5. Insert the tote bin bubblers and turn them on, placing one bubbler directly next to the “tea bag” and one at the lowest corner of the tote.

  6. Begin adding the compost mixture slowly to the “tea bag” as the tote continues filling with water.

  7. Add 1 cup each of trace minerals, green sand, and kelp into the tea bag.

  8. Continue slowly adding the compost mixture into the “tea bag” a little at a time.

  9. Once the tote is approximately 200 gallons full, add ½ cup to 2 cups molasses into the tote. If the ambient temperature is below 60 degrees, then more molasses will be needed. If the temperature is greater than 60 degrees, then less molasses will be needed.

  10. Add remaining compost mixture into the “tea bag.” Check for clumping. Carefully maneuver the “tea bag” bubbler to ensure the compost is properly aerated.

  11. Ensure that the tea bag bubbler is working properly and add the PVC cap.

  12. Check your compost tea over the next six hours to ensure all bubblers are working properly. Stir the tea using the bubblers.

  13. After an additional six hours, remove the tea bag from the bin and return only the tea bag bubbler to the bin.

  14. Spread the bubblers throughout the brew bin.

  15. Monitor compost tea over the next 24-48 hours, stirring the tea with the bubblers with every morning check.

  16. Begin microscope testing the compost tea after 24 hours of brewing (see microscope testing section below)

  17. Because the tea contains living microbes, it must be used immediately. For this reason, we recommend scaling your brewing operation to size your needs.

Microscope Testing

or best results and maximum fun, use a microscope to check out the microbial life form you’ve grown in your compost tea. You’ll need a microscope with a 100x lens. First, stir the tea using one of the bubblers. Using a clean pipette, draw tea from at least three locations around the tote bin. Place 3 to 5 separate drops of tea onto a clean microscope slide. Cover with a cover slip and observe the sample drops under the microscope. Look for the presence of bacteria, fungi, protozoa, and nematodes. Observe a minimum of five fields from at least three drops of tea (a field is defined as what you can see in the microscope).

When testing compost tea, refer to the Compost Tea Quality: Light Microscope Methods by Elaine Ingham, Ph.D., Soil Foodweb Inc.

Observations – Qualitative Testing of Compost Tea

Bad — Zero to a few organisms observed – less than 25 bacteria observed in each field
Poor — More than 25 bacteria, but less than 500 bacteria seen in each field
Acceptable — In the first 10 fields, at least one fungal hypha should be seen, preferably a thick hyphal strand that goes across the full field of view. If only bits of hypha are seen, then the sample is still in the poor category. More than 500 bacteria per field should be observed. Protozoa should be observed skimming across the sample.
Good — In the first 5 fields, a fungal hypha should be seen and preferably more than one in that volume of liquid. Thousands of bacteria should be present in each field. Several protozoa should be seen, preferably more than one kind of protozoan – such as several species of flagellate or amoebae.
Excellent — Each field should contain a strand of fungal hypha. Thick strands are better than skinny ones. Just like “good” tea, the bacteria should be everywhere and too numerous to count easily. Protozoa should be dense with several individuals observable per field. In “Excellent” tea, nematodes will be found as well.

Barn2Door Admin