How To Make Compost Tea

Posted by Amy Storey on November 15, 2016

Tim Minor runs the Edible Learning Lab in Buffalo, Wyoming. Today he’s going to show us how to use vermicast to make a compost tea for soil beds or planters.

compost tea tim minor edible learning lab

Vermicast is worm castings, a nutrient-rich material that can be used to make “compost tea” or “worm tea”. The tea can be used as a soil drench in raised beds. Compost tea offers the benefits of compost without adding the actual compost to your soil. This can be faster than using compost and convenient if you have limited space for new soil in your beds.

Worm tea or compost tea is best for small-scale soil growers. Although compost tea can be used in hydroponics, it can pose a health issue which interferes with some certifications. On a commercial scale, compost tea can be too inconsistent to quantify. This makes it hard to keep nutrient levels (and therefor yield) steady.

*Note on water source: Buffalo uses sodium hypochlorite to reduce bacteria in the municipal water. Since Tim is trying to increase bacteria, he needs to neutralize that. He uses food grade ascorbic acid (Vitamin C) and pH Up to neutralize the sodium hypochlorite and then bring pH back up to about 6.5.

Materials needed for compost tea

  • Worm castings (vermicast). You can build or buy worm bins. 
  • Molasses. A few tablespoons will do. This measurement doesn't need to be exact. 
  • Cheesecloth. You can get this at any home or kitchen store. Double fold it when you tie it up!
  • Zip tie. String also works, but zip ties are easier to use.
  • S-hook. 
  • 5-gallon bucket. Any water-holding container will work here.
  • Aeration pump. Or air stone. This will help you avoid anaerobic decay.

compost tea materials needed

How to make 5 gallons of compost tea

1) Treat water if necessary and add molasses.

If the city treats your water with an antibacterial substance, you might need to treat it. If you use an RO filter on your farm, then use RO-filtered water.  

Molasses will "feed" the bacteria as they multiply in the solution you're creating. Add ~2 Tbs per 5 gallons.

2) Tie up castings into cheesecloth bag with a zip tie.

You can purchase cheesecloth at any home store or online. Double the cheesecloth over and pour the castings into the center, leaving at least a 2-inch margin. 

Gather the margins of the cheesecloth and secure with the zip tie. 

compost tea

3) Use S hook to hang on the side of the bucket with the bag in the water. 

Tie the cheesecloth to the S-hook so that it can be dangle from the side of the bucket.  

4) Put aeration stones into the bucket. 

Use a simple aeration pump with air stones to aerate the water while the compost soaks. This will help decrease the chance of anaerobic decomposition. 

5) Let the compost sit for 24 hours.

Leave the compost tea in the bucket for 24 hours. If you don't have aeration stones, the bucket should only be left for 4-6 hours.

6) Dilute 1 part tea to 5 parts water to drench.

A 5-gallon bucket of compost will make about 25 gallons of drench. You can use this to water your crops in soil beds. We don't recommend using compost tea as a foliar spray, which can be a sanitation issue.

Learn more about classroom gardening

Classroom gardens offer students hands-on learning, healthy food, and lessons that extend beyond the classroom. The Edible Learning Lab taps into dozens of opportunities through their 8-part lab and curriculum

If you know of students or schools who would benefit from this rich learning environment, help them get started.

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