How to Make Compost Tea? Easy Step-by-Step Instructions

Plus, tips on how to use it and variations.

A person putting hands in a compost bin.

Annie Otzen / Getty Images

Overview
  • Working Time: 20 minutes
  • Total Time: 1 - 2 days
  • Yield: 4 gallons compost tea
  • Skill Level: Beginner
  • Estimated Cost: $0

Compost tea is an eco-friendly organic fertilizer solution that plays an important role in sustainable agriculture. With untreated water, a few simple tools, and time, you can transform your food and garden waste into a nutritious liquid fertilizer for plants.

Not only does compost tea encourage healthy plant development, but it also protects them from certain pathogens. Plus, compost tea is inexpensive and sustainable—as long as you have compost, you can make it. And if you compost your own food scraps, it’s essentially free fertilizer.

You don’t have to be a large-scale grower to reap the benefits of compost tea. If you have a compost pile (or access to a neighbor’s), you can make this nourishing elixir for your own plants. Making it is easy and relatively hands-off.

What Is Compost Tea?

Compost tea at its most basic form is water infused with organic compost. It’s a brewed liquid that concentrates bacteria, fungi, and other organisms to create an easily absorbed, nutrient-dense liquid. Gardeners and farmers use compost tea, often referred to as black liquid gold, to fertilize their plants.

Compost tea has a number of agricultural benefits. Most importantly, it boosts plant health. Good compost tea can also improve soil health and structure and stimulate plant root growth.

You can purchase pre-made compost tea at some garden retailers, but making your own is remarkably simple and inexpensive. Simply follow these easy instructions.

What You'll Need

Ingredients

  • 3 to 4 gallons non-chlorinated water
  • 2 to 6 cups compost

Equipment/Tools

  • 5 gallon bucket
  • Shovel
  • Strainer
  • Spray bottle

Instructions

  1. Scoop Compost Into Bucket

    Dip your shovel into your compost pile and scoop up between 5 and 10 cups of fully finished organic compost. Add that to your empty bucket.

    Compost takes between 4 and 12 weeks to fully finish. You’ll know it’s ready when it reaches a rich, dark brown color, its texture is crumbly, and it smells earthy. If the compost smells bad, is still warm, or you can clearly see food content, it’s probably not finished.

    Warning

    Do not use unfinished compost in your compost tea. Unfinished compost may contain pathogens that could damage plants. It competes with plants for nitrogen and may hinder their growth and seed germination.

  2. Add Non-Chlorinated Water

    Chlorine can kill microbes in compost, so it’s no good to use to brew compost tea. After all, microbes are the star players in compost tea—killing them would render the solution useless. 

    Rainwater is a great eco-friendly solution. Rainwater is untreated, so you won’t need to worry about added chlorine. You can also use tap water that has sat out for at least a day to allow the chlorine to evaporate.

    Dump about 4 gallons (or however much will fit in your bucket) of unchlorinated water on top of the compost in your bucket.

  3. Mix Solution

    Use your shovel or a stick to mix the compost and water together, making sure all of the compost gets completely submerged in water. Stir the mixture several times so that the compost and water are thoroughly combined and let the microbes work their magic.

  4. Set Aside

    Once the compost and water are mixed, it’s time for them to brew. Set the bucket aside somewhere that’s not in direct sunlight, like in a corner on your patio or in your garage, and let it sit. If the tea is left in the sun, it could heat up and encourage the growth of harmful bacteria, like E. coli and salmonella.

    Cold temperatures, rain, and snow can also negatively impact the tea, causing it to take longer to brew and potentially killing microbes.

    The amount of time your tea will take to brew depends on the air temperature outside. If it’s above 60 F, let the mixture sit for 12 to 36 hours. The lower the temperature, the longer you should let it brew. In temperatures below 60 F, you may need to leave it for up to 72 hours.

    Stir the mixture once or twice a day to introduce oxygen into your liquid, which will help nutrients accumulate.

  5. Strain Compost Out

    After a few days, your compost tea should be finished brewing. You’ll now need to strain out the compost from the liquid, leaving you with nutritious compost-infused water. This is your finished compost tea.

    Return the leftover compost to your bin or use it as mulch around your plants to help them retain moisture and prevent weed growth.

  6. Dilute the Mixture

    If your compost tea isn’t very dark in color, you don’t need to dilute it. However, dark brown to black compost tea should be diluted with fresh water. Dilute the tea to at least a ratio of 1:3. This helps the tea go further and ensures that it’s not too strong for plants—giving them too many nutrients can do more harm than good.

  7. How to Use Compost Tea

    Pour your finished compost tea, diluted as needed, into a spray bottle and use it as soon as possible. The finished tea will immediately begin to lose nutrients, so it lasts less than a week. 

    You can spray the mixture directly onto plant leaves or onto the soil surrounding the plant, allowing it to completely drench and soak into the soil. Apply a cup or two of the mixture to each plant.

    Compost tea primarily made from plant waste can be applied to plants multiple times a week. If it's made from manure, however, it's a different story—compost made from manure contains a significant amount of nitrogen, which can actually burn plants when exposed too much. Manure compost tea should only be applied once a week.

Variations

This is a very easy, basic DIY compost tea recipe. Once you’ve mastered the basics, there are a few compost tea variations you can try that can boost the substance’s nutrient content even further. 

Compost Tea Additives

There are several things you can add to your compost tea to make it more beneficial for your plants. Mineral, organic, and biological additives have been shown to stimulate microbial activity in compost, which makes the substance even more nutrient-dense.

  • Wood chips, sawdust, and crushed branches aerate the compost, allowing aerobic organisms to breathe and encouraging microbes while reducing the risk of pathogens.
  • Kelp, fish hydrolysate, and molasses act as a food source for microbes.
  • Cornstalk, sawdust, or spent mushroom substrate can offset high moisture content if you’re using wet compost to make the tea.
  • Adding ashes increases the mixture’s ability to hold moisture, which comes in handy if you’re using excessively dry compost.

Aerated Compost Tea

Aerating compost tea encourages good microbes and reduces the risk of pathogens. Aerobic organisms are the most beneficial to plants because they promote the processes that a plant needs to grow strong and stress-free. Aerating your compost tea will ensure that those beneficial aerobic organisms can survive.

Aerating your compost tea is a bit more involved than the above method. You'll need to add an aquarium aerator to introduce oxygen into your brew. You can also use an air stone or bubbler to get the air from the pump down into your bucket or another brewing container. 

Insert the aerator or air pump into the bucket so that it rests on the bottom and run it in the compost tea for 12 to 48 hours. Then, immediately use the compost tea to fertilize your plants.

View Article Sources
  1. Gonzalez-Hernandez, Ana Isabel, et al. "Compost Tea Induces Growth and Resistance Against Rhizoctonia solani and Phytophthora capsici in Pepper." Agronomy, vol. 11, no. 4, 2021, 781., doi:10.3390/agronomy11040781

  2. Barthod, Justine, et al. "Composting with Additives to Improve Organic Amendments. A Review." Agronomy for Sustainable Development, vol. 38, 2018, pp. 17., doi:10.1007/s13593-018-0491-9