What Is Compost Tea and How to Make It

Written By Jenn

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Compost tea is a a natural, cost-effective way to boost your garden’s productivity while promoting plant health!

This nutrient-rich elixir has been gaining popularity among gardeners for its ability to improve soil health, increase plant resistance to pests and diseases, and promote robust growth.

So, “what is compost tea”, what is its composition, benefits, and how you can make your own at home?

Key Takeaways

  • Compost tea is a liquid solution of beneficial microorganisms that help promote plant health and soil quality.

  • Brewing methods, equipment, and microbial food sources should be used to create compost tea for maximum impact in the garden.

  • Safety considerations such as monitoring quality, understanding shelf life, properly cleaning and sanitizing equipment must be followed when using compost tea.

Understanding Compost Tea

Compost tea is a liquid solution made by extracting beneficial microorganisms from compost, such as bacteria, fungi, and protozoa.

Incorporating compost tea into your garden soil and houseplants significantly reduces the need for synthetic fertilizers, which leads to healthier plants and a more sustainable garden.

Using compost tea bags can make the process of brewing compost tea even more convenient for gardeners.

So, what makes compost tea so special?

The secret behind compost tea’s powerful effects lies in its diverse range of beneficial microorganisms, as well as soluble nutrients that promote plant growth and health.

These microorganisms are key in maintaining healthy soil, enhancing moisture retention, and encouraging nutrient uptake in plants.

The brewing process used to make compost tea extracts these valuable components from high-quality compost, such as worm castings or well-aged compost, ensuring that your plants receive the best possible nourishment.

The Composition of Compost Tea

The composition of compost tea is quite fascinating. It consists of a variety of beneficial bacteria, fungi, and other microorganisms.

Compost tea also contains soluble nutrients that are derived from the compost used in the brewing process. These nutrients help to nourish the plants and improve soil structure, further boosting plant health and productivity.

When making compost tea, using high-quality compost rich in organic matter and diverse microorganisms is vital.

This can include worm castings or well-aged compost, both of which are excellent sources of microbial life and nutrients.

Using such ingredients, your compost tea will be teeming with beneficial microorganisms and nutrients that will help your plants thrive.

Making Your Own Compost Tea

how to make compost tea

Making compost tea at home is a relatively straightforward process, involving three main steps.

  1. Choosing quality compost
  2. Using appropriate brewing methods and equipment
  3. Adding microbial food sources to encourage microbial growth.

Use good quality compost. If you are buying compost rather than using your own, make sure that it is OMRI listed.

This ensures that your compost tea, made from a well-maintained compost pile, will be free of contaminants and harmful pathogens.

Next, you’ll need to decide on a brewing method.

There are two main methods for brewing compost tea: aerated and non-aerated.

Aerated compost tea is generally faster and more effective, as it promotes the growth of beneficial microorganisms through increased oxygen levels.

For this method, you’ll need equipment such as an air pump, an air stone, and permeable bags for brewing.

The bags shown below are specifically for brewing compost tea.

Compost Tea Filter Bags

1. Choosing Quality Compost

Using compost that is rich in organic matter and diverse microorganisms, such as worm castings or well-aged compost, is necessary for optimal results.

Well-aged compost has had time to decompose and become more nutrient-dense, making it an excellent choice for compost tea.

2. Brewing Methods and Equipment

As previously mentioned, compost tea can be brewed using two main methods: aerated and non-aerated.

Aerated compost tea is generally faster and more effective, as it promotes the growth of beneficial microorganisms through increased oxygen levels.

Non Aerated Compost Tea

The simplest way to make non-aerated compost tea requires just compost, clean tap water, a mesh bag, and a bucket. It is made in the same way as aerated compost, just omitting the air stones and pump. It can also be left longer to “steep”.

Suspend a bag of compost or manure in a bucket of water for a few days, allowing the water to darken, and then using it as a high-nutrient water for plants.

Ingredients and Equipment To Make Aerated Compost Tea

  1. Compost: High-quality compost rich in organic matter.
  2. Aeration Equipment: You’ll need an air pump, an air stone, and tubing.
  3. Water: Non-chlorinated water (if possible) to avoid killing beneficial microbes.
  4. Food Source: Molasses or another simple sugar (optional but helps feed microorganisms).
  5. Filtering Bag or Cloth: To contain the compost.


1. Prepare the Ingredients

  • The compost should be well-aged and have a pleasant, earthy smell.
  • Fill a bucket or container with water. Allow it to sit for 24 hours to dechlorinate. If using tap water, the chlorine will evaporate over this time.

2. Setup Aeration Equipment

  • Connect the air pump to the tubing and attach the air stone at the other end.
  • Place the air stone in the bottom of the container where you’ll be brewing the compost tea.

3. Prepare Compost Tea Bag

  • Fill a mesh bag or a piece of cloth with compost. Tie it securely to form a “tea bag.”

4. Brewing the Tea

  • Submerge the compost tea bag in the container of water. Ensure the water is filled but leaves enough room for aeration without overflowing.
  • Add a food source like molasses to the water. This step is optional but helps to feed the microbes and enhance their growth.

5. Aeration Process:

  • Turn on the air pump and let it run continuously during the brewing process. Aeration oxygenates the water, creating an ideal environment for beneficial microorganisms to multiply.

6. Brewing Time

  • Allow the compost tea to brew for 24-48 hours. Keep the container in a warm, dark place and maintain a consistent temperature for the best results.

7. Monitor and Adjust

  • Throughout the brewing process, monitor the tea for any unpleasant odors or signs of anaerobic conditions (like a rotten egg smell).
    If this occurs, adjust the aeration or compost-to-water ratio.

8. Strain and Apply

  • After 24-48 hours, turn off the air pump and remove the compost tea bag.
  • Strain the liquid through a finer mesh or cloth to remove larger compost particles.
  • Use the finished aerated compost tea immediately by diluting it (usually 1:10 ratio with water) and applying it to your plants as a foliar spray or soil drench.

9. Cleanup

Clean all equipment thoroughly after use.

What is an Air Stone?

An air stone is a small device used in fish tanks and aeration systems to diffuse air into water in the form of fine bubbles.

It is commonly made from porous materials like wood, ceramic, or porous stone. The air stone connects to an air pump via tubing and when air is pushed through the air stone, it creates a stream of tiny bubbles. It is common to see these streams of tiny bubbles in fish tanks.

Next time you are in a waiting room and there’s a fish tank, check out the air stone.

These bubbles increase the oxygen level in the water, providing aeration which is essential for various applications, such as in fish tanks, hydroponic systems, and in the production of aerated compost tea.

In the context of making aerated compost tea, the air stone helps oxygenate the water to create an optimal environment for beneficial microorganisms to thrive and multiply during the brewing process. Yay!

During the aeration process, the water surface should have numerous bubbles and appear lively and stirred.

If the air flow decreases during the brewing process, lift the air stone and give it a thorough scrubbing before replacing it in the bucket.

3. Adding Microbial Food Sources

In addition to using good quality compost, it’s important to add microbial food sources to your compost tea to stimulate microorganism growth and diversity.

Add approx 1/4 to 1/2 a cup to a 5 gallon bucket of compost tea.

Here are some examples of microbial food sources that may be used in the preparation of compost tea:

  • blackstrap molasses

  • natural sugarcane

  • maple syrup

  • fruit juice

  • oat flour

  • kelp meal

  • alfalfa meal

Incorporating these food sources into your compost tea provides the necessary nutrients for beneficial microorganisms to thrive, ultimately leading to healthier plants and improved soil fertility.

Using Compost Tea in Your Garden

use compost tea in a watering can

Once you’ve brewed your compost tea, it’s time to put it to work in your garden.

There are two main ways to apply compost tea, either as a soil drench to improve soil health, or as a foliar spray to boost plant resistance to pests and diseases.

Both application methods offer unique benefits to your healthy plants and garden, and you may choose to use a combination of both for maximum impact.

Then you can sit down and have a cuppa yourself – I recommend English Breakfast tea.

Soil Drench Application

Applying compost tea as a soil drench involves diluting the tea with an equal volume of water, then pouring it directly onto the soil around the base of your plants.

This method of using the compost tea allows the plants to absorb the beneficial microorganisms and nutrients present in the compost tea through their roots, improving soil health and promoting robust growth.

Foliar Spray Application

You can apply compost tea as a foliar spray, which involves diluting the tea with water (to a ratio of 1:4 up to 1:10) and spraying it directly onto the leaves of your plants. This method allows the plants to absorb the valuable nutrients and beneficial microorganisms directly through the foliage.

When applying compost tea as a foliar spray, using a garden sprayer ensures even coverage and that the tea reaches all parts of the plant.

Remember that the ideal time to apply compost tea as a foliar spray is during the morning when it is cooler, as bright sunlight may harm the beneficial microorganisms present in the tea.

How Often To Use The Compost Tea

As a general guideline, it’s recommended to apply compost tea on a quarterly basis. For optimal results, apply the tea at the first sign of true leaf development, and again one and two months later.

Safety and Best Practices Using Compost Tea

use compost tea as a foliar spray

Ensuring the safety and effectiveness of compost tea is of paramount importance when using it in your garden.

This involves monitoring the quality of the tea, understanding its shelf life, and properly cleaning and sanitizing equipment used in the brewing process.

Ensuring Compost Tea Quality

Using high-quality compost that is rich in organic matter and diverse microorganisms is crucial to ensure the quality of your compost tea.

Proper aeration during brewing is key to promoting the growth of beneficial microbes and preventing the growth of harmful bacteria.

Avoid using contaminated equipment or water sources that could introduce harmful pathogens or contaminants into your compost tea.

Storage and Shelf Life

Compost tea has a short shelf life, typically around 4 hours, and should be used immediately after brewing to maintain its effectiveness.

If you’re unable to use your compost tea within this time frame, it’s important to store it properly to preserve its potency and freshness.

The ideal storage for compost tea is in a sealed, opaque, and airtight container, preferably stored in the refrigerator.

Storing your compost tea in these conditions, will help to maintain its potency and ensure that it remains safe and effective for use in your garden.

Cleaning and Sanitizing Equipment

Prevent cross-contamination and ensure the safety and quality of your compost tea. After brewing aerated compost tea, clean all tools and equipment with soapy water.

good quality compost to make compost tea

Frequently Asked Questions

How do you make compost tea?

To make compost tea, start by gathering supplies such as non-chlorinated water, fully finished organic compost, unsulfured blackstrap molasses, liquid kelp fertilizer or kelp meal, and liquid fish fertilizer.

Then, put the compost in a mesh bag and place it in a bucket with the other ingredients before letting the mixture steep in a cool, dark place for one week, stirring it daily. (Note, this is compost tea that has not been aerated)

What is compost tea made of?

Compost tea is a liquid produced by steeping compost in water and extracting beneficial microorganisms, such as bacteria, fungi, protozoa, nematodes, and microarthropods.

What is the disadvantage of compost tea?

Compost tea can generate very high microbe populations, however, there is little control over the types of bacteria from batch to batch, and a risk of building pathogenic populations depending on the organisms in the original compost.

What is the main difference between aerated and non-aerated compost tea?

Aerated compost tea is generally faster and more effective, as it encourages the growth of beneficial microorganisms through increased oxygen levels, while non-aerated compost tea may contain harmful pathogens.

vector - composting worm
Looking forward to that compost tea! I’m thirsty!

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