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Working with Nature to Build Organic Soil, Part 4: Compost Tea

Previous articles in this series (Part 1, Part 2, Part 3)  told how nature works with plants and soil microbes to create soil from atmospheric carbon. We’ve seen how to follow nature’s example, by using cover crops and compost, to create organic soil and nutritious food. In this article, I’ll discuss one more way of working with nature by using compost tea.

What is Compost Tea?

This tea is an aerobically prepared solution that contains both the microbes and nutrition necessary for healthy soil and healthy plants. The process of making compost tea greatly multiplies the number of microbes present and puts them in a soluble form for easy application.

What Are the Benefits of Compost Tea?

1. Unlike compost, compost tea is a liquid and can therefore soak into the ground where it is most effective.

2. Compost tea is easy to apply from a watering can or a sprayer.

3. Making compost tea is an inexpensive way to quickly multiply microbes. A small amount of compost becomes compost tea that can nurture many plants. One teaspoon of soil contains about a billion bacteria but one teaspoon of compost tea contains about four billion bacteria!

4. Compost tea helps control plant diseases. Spray it on the underside of leaves where plants have openings (stomata) for CO2 and O2. Because the stomata are most susceptible to bacterial and fungal diseases, the “good microbes” in the tea actually help prevent disease. Here’s a testimonial on growing heirloom Heinz tomato plants with and without compost tea! In our garden, this variety routinely contacted a fungal disease by late August. Since using compost tea, the plants grow much larger, never show signs of disease and keep producing until heavy frosts.

5. During this spring season, I am now totally dependent on compost tea to feed the garden seedlings that were begun as seeds in our sun-room. Seeds have adequate nutrition for emerging seedlings until plants get their secondary leaves. Compost tea then provides the microbes and nutrition that seedlings need both to grow and to establish a relationship with soil microbes.

6. Compost tea can be made with the simple recipe, below, or you can continually learn more to modify how you feed your garden plants or orchard. Lowenfels’ and Lewis’s book, Teaming with Microbes, is a good place to get the basics.

Materials for Making Compost Tea in a 5-Gallon Pail

• 4 cups compost or vermicompost    
• 2 tbsp unsulfured molasses
• 2 tbsp liquid kelp
• 3 tbsp liquid fish
• Unchlorinated water (If you don’t have access to unchlorinated water, oxygenate the water for two hours before adding other ingredients, or use a charcoal filter).

How to Make Compost Tea

Getting your equipment and ingredients together the first time is a bit of a hassle, but then it’s easy to continually produce compost tea throughout the growing cycle.

You’ll need a clean 5-gallon bucket. A lid is helpful to keep out light, but you can instead place a towel over the top of the bucket while the tea is brewing.

equipment for compost tea

A pet store will provide some of the necessary equipment. You’ll need an aquarium pump large enough to run two sets of air stones, about eight feet of air tubing and air stones. (See photo). This equipment is essential because brewing compost tea is an aerobic process. A garden store can then provide both liquid kelp and liquid fish.

If you don’t have good compost available, vermiculture, or “worm compost,” can be used instead to make compost tea.

It’s most convenient to place the compost, along with the two smaller air-stones, in something that serves as a “tea bag.” That way, you won’t have to strain the tea before using it in a sprayer or a watering can. Pantyhose are recommended, but we use inexpensive paint-strainer bags found at hardware stores.

In addition to using this sketch to assemble your equipment (see photo, below), here are a couple suggestions you’ll find helpful. Keep the pump higher than the air tubing at all times so water doesn’t back up into the pump. Place the small stones and tubing at the bottom of your “tea bag” before adding the four cups of compost. After that, tie the bag shut and suspend it by that string to the handle of the bucket. Holes can be drilled in the bucket and lid for the string and tubing to go through, but it works fine to have them come over the lip of the bucket with a cover placed lightly on top.

compost tea #1

Compost Tea Caveats

• Make compost tea at room temperature and out of direct sunlight.
• In making compost tea, you are dealing with living organisms and an aerobic process. Bubble oxygen through the mixture from 24 to 48 hours. Longer than that and the microbes will run out of food.
• Use the tea within a few hours of completion so the microbes won’t run out of oxygen.
• Don’t apply the compost tea to plants in direct sunlight—the microbes in the tea won’t survive.
• You’re not “foliar feeding” plants by spraying leaves, you are offering protection from “bad” bacteria and fungi. Foliar feeding actually breaks the synergistic relationship between plants and the living soil.
• You cannot apply too much compost tea. Go ahead and keep using it through the growing season.

I don’t believe human technology can come close to what nature has devised to nurture healthy plants, produce, soil and planet. By working with nature and using cover crops, compost and compost tea, we can be a successful part of nature’s plan.

Cross-section sketch.

Mary Lou Shaw is a retired family practitioner who emphasized preventive medicine, is now homesteading with her husband in Ohio. Besides growing their own food, the pair help preserve genetics and knowledge needed by others to foster rare breeds. They have a large garden and orchard, Dorking chickens, Narragansett turkeys, Dutch Belted cows and bees. Buy Mary Lou’s book, Growing Local Food, through Carlisle Press at 800-852-4482. Read all of Mary Lou's MOTHER EARTH NEWS posts here.

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