Home Gardenign Center Tip Sheet: Compost Teas

By Sonia Uyterhoeven

·· Soil & Compost ··


Compost Tea

Compost tea is fashionable again. In the past, compost tea involved soaking compost in water for several days to several weeks until it smelled rather rancid and then pouring it on your plants.

Today, aerated compost tea is all the rage. Aerated compost teas take a little bit more work to make, but the bonus is that they smell nice and are full of microorganisms that help make nutrients available for plants and protect them from diseases. Compost teas supply your soil and plants with an army of beneficial organisms that will help fight off pests and pathogens and provide nutrients.

Compost teas are made by adding compost and additional nutrients to de-chlorinated water and aerating the mix for 1 to 3 days. Compost tea brewers ranging from 5 to 20 gallons are available on the market, but you can also make one at home with a few supplies. Remember these teas are for your plants and not your own consumption.

Supplies: 5-gallon plastic bucket, an aquarium air pump with two air outlets, four air stone (one set 1-inch, one set 5-inch), plastic tubing with either T-valve attachments or a gang valve (distributes air), and cheese cloth or a porous bag to hold the compost.

Attach the air pump, plastic tubing, and air stones as you would when assembling an aquarium. You can either use T-valves to branch your setup into four tubes with air stones placed on the ends or you can hang a gang valve on the edge of the container and run the tubes through it for similar results. Place the air stones in the 5-gallon plastic bucket with water and aerate for 1/2-1 hour to de-chlorinate the water.

In the porous bag add high quality compost* and additional nutrients. Place the smaller air stones in the bag and suspend the sac in the water. The larger air stones remain in the water. You can also mix the compost together with the water, but will have to strain it with cheesecloth when you apply it to your plants. The ratio of water to compost will vary depending on the recipe you are following--a good ratio is 5:1.

You need to aerate the mixture, the water temperature should be average room temperature (around 75 degrees Fahrenheit) and you will need additional nutrients to feed the microorganisms. The goal is to achieve good aeration (a nice vigorous bubbling action). Once brewed, your tea will need to be used within 2 to 8 hours to keep it as an anaerobic process. The tea itself can be left brewing and aerated for several days.

The science of soil biology states that short season crops (annuals) need soil with a high bacterial content. Long term crops (perennials, shrubs and trees) do best in soils with a high fungal content. Grasses fall somewhere in the middle. Teas can be made according to your garden’s needs.

To brew a tea high in bacterial content add molasses, maple syrup, fruit juice, and fish emulsion (about 2 tablespoons for 4 tp 5 gallons) to feed the bacteria. Bacterial compost teas take less time to make and can be ready in 18 to 36 hours. Adding a capful of vegetable oil (not olive or canola both of which have anti-microbial properties) will help reduce foaming. Remember when making bacterial teas to make sure that you are creating an aerobic (oxygenated) process so that you create a healthy brew. Avoid fresh manures in your compost and, since you are working with live microorganisms, avoid spraying the tea on edible crops unless it has been tested.

To brew tea with high fungal content add kelp (e.g. Eco-Nereo Kelp), oatmeal, humic acid (e.g. TerraVita®), and fish hydrolysate (e.g., Neptune’s Harvest™). Orange, apple, or blueberry pulp will also help to grow the fungal content. The fungal components in a tea will only start to grow after 12 hours and typically take 24 to 48 hours.

One way to encourage fungal growth in your tea (if you are making tea for perennials or woody plants) is to create a slurry out of flour and water (approx. 1/4 cup flour mixed with water to form a paste) and add it to the tea. Another way is to create a mix of moist compost and oatmeal (ratio 3 to 4 tablespoons oatmeal per cup of compost) in a Tupperware® container and place it in a warm, dark place for three days.

Apply compost teas as a soil drench to your woody plants in the spring and again in the fall. Lawn applications can be done every 2 weeks in the spring and then every month in the summer. Applications for annuals and perennials can range from once a week to once a month.

It is important to spray your plants (foliar application) when they need food at the beginning of a growth cycle, for example at bud break and just before the development of fruits and flowers. You can never use too much compost tea and home brews will be weak.

The best time to spray compost tea is once the weather starts to warm in the spring. If it is too cold, the microbes will be inactive. Overcast days are much better for applications than sunny days. When applying teas avoid the heat of the day and spray either in the morning or the late afternoon.

Applications can be diluted up to five times, a little will go a long way. Apply either with a plastic watering can or with a sprayer.

It is important to clean out your spraying and brewing equipment immediately after use, otherwise a slime or film will form on the containers. If the bacterial slime has dried on your equipment, use a 5% baking soda solution to clean up your mess.

For more information on compost teas visit the website of the Institute of Ecosystem Studies. Dr. Elaine Ingham has a comprehensive manual on compost tea. You can send your teas out to organizations to test for the content and health of your brew. It is also important to get your soil tested periodically so that you know how to fertilize and amend your soil. Take a sample and send it to your local co-operative extension.

* High quality compost: Compost that is free from pesticides; has been properly heated and aerated during the decomposition process; and is a good moist balance of green (nitrogen based) and brown (carbon based) material. Greens = vegetable scraps, green plants, and weeds. Browns = fall leaves, dead plants, straw, shredded newspaper, old potting soil, and stale cereal.

Download this Tip Sheet.

·· Soil & Compost ··



Generous support for the Home Gardening Center has been provided by Kenneth and Ellen Roman.