How to Make Compost Tea

Learn to make your own organic fertilizer by brewing compost tea at home.

Fertilize Zucchini Plant Once Blooms Appear

Fertilize Zucchini Plant Once Blooms Appear

Photo by: DK - Ready Set Grow! © 2010 Dorling Kindersley Limited

DK - Ready Set Grow! , 2010 Dorling Kindersley Limited

Compost tea is a fantastic way to protect plants with a cover of beneficial microorganisms and feed the roots as an organic fertilizer. Compost tea is a mixture of nutrients and oxygen-loving (aerobic) bacteria, fungi, nematodes and other microbes that live in finished compost. It takes time to separate these organisms from compost, which is why compost tea is made by steeping compost in water for a day or more. 

To create your own compost tea brewer, you’ll need:

Finished compost

This can be store-bought or homemade, as long as it’s completely finished composting. Finished compost has a sweet smell. The amount of compost needed varies depending on the amount of tea you’re brewing. For a 5-gallon batch, you’ll need about 4 cups of compost. A batch in a 25-gallon trashcan will need about 20 cups of compost. Avoid composts that contain animal manure, as it may harbor e-coli bacteria. Although the tea-making process should kill e-coli, it’s better to be safe than sorry. Worm compost is safe for tea brewing.

Bag or sock (optional)

Containing compost in a suitable mesh bag or sock helps keep the tea free of organic matter that may clog up a mister or watering can later on. However, you don’t need to bag the compost in order to make compost tea – you can always strain the compost out after brewing or add the compost along with the tea if you’re planning on applying as a soil drench. Repurposed pantyhose make a great compost sock, although an old t-shirt, pillowcase, burlap bag or cheesecloth can also be used to make a suitable bag.

Microbe food

Your population of bacteria needs sugar to grow. Sweet and sugary non-sulfured molasses, maple syrup, cane syrup or fruit juice are all good options for microbe food. Add about 2 tablespoons for every 5 gallons of water.

Dechlorinated water

Chlorine kills the microbes needed for healthy compost tea. Allow chlorine to evaporate slowly over 24 hours. Or inject with oxygen from an air pump for two hours to quickly dechlorinate water.

Oxygen

This ingredient is easily added with a simple (yet sufficiently large) air pump that includes tubing, a splitter, check valve and at least two air stones. The larger the bucket, the larger the air pump you’ll need. Oregon State University Extension suggests using an 18w air pump when brewing in a 5-gallon bucket, although other sources say that a large aquarium pump should do the trick. On the other hand, in their book Teaming With Microbes, Jeff Lowenfels and Wayne Lewis recommend using a 1/3 horsepower air pump and substituting air stones with a 2-foot length of 1/4-inch soaker hose to brew in a 30 gallon trashcan. 

Bucket

Beginner brewers should get their feet wet by trying their first batch in a 5-gallon pickle bucket. As your interest and compost tea needs grow, you can always brew in a bigger container. Repurposed plastic drums, trashcans and other containers have been used for successfully brewing compost tea. Remember, the bigger the container, the more oxygen and compost you’ll need. 

Time

Depending on the types and proportions of each ingredient added, brewing compost tea can take anywhere from one to three days. Remember, UV rays kill microbes, so brew your tea out of direct sunlight. Finished tea looks a bit like coffee and smells really sweet and earthy. Use your tea within four hours to keep your microorganisms alive. Need more time? Keep the air pump running or refrigerate until you’re ready to use.

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