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Compost Tea – What and Why

What is compost tea? Why is compost tea good for my organic garden?

This post is the second of four articles about Compost and Compost Tea. If you haven’t already done so, read all about Compost: what it is and why you want to use it. After this post, head over to read How to Make a Compost Tea Brewer. Then mosey on over to read How to Make and Distribute Compost Tea.

We have gardened organically for 15 years. We add compost to our beds each spring and apply compost tea to the garden twice a week once during the growing season.

We’ve seen the benefits of both compost and compost tea with our own eyes and we are believers. We used to purchase compost tea from a local organic gardening store, but we found ourselves going through so much that my husband built a 35-gallon compost tea brewer and we’ve started brewing our own!

So, let’s start from the top:

 What is compost tea?

What’s the difference between compost and compost tea?

Why is compost tea good for my garden?

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Quick Recap of Compost

Most, if not all, gardeners are familiar with compost – that decomposed organic matter like leaves, grass clipping, and fruit and veggie scraps from the kitchen that we so love to add to the soil in our garden. We’ve been taught that adding compost to our soil every year enriches it with nutrients, adds and feeds the diverse bacterial and insect life of our soil, and improves its ability to retain moisture thereby making our garden plants happy and healthy.

Many of us, my family included, have even taken the step of making our own compost by using the discarded or unused organic table and yard scraps – leaves, grass clippings, coffee grounds, veggie and fruit peels, etc and adding them to our compost bin. This one is similar to ours and sits behind the garage. In late winter/early spring we gleefully fill our wheelbarrow full of this black gold to work into our garden soil.

What’s not to like about that? Reduce waste, conserve and be prudent stewards of our planet, and at the same time provide excellent nutrients for our garden. I get that…..but compost tea????

For a more in-depth discussion of compost, head over to Compost: What it is and How to Make it.

What is Compost Tea?

Compost Tea being dispensed from DIY Compost Tea Brewer
DIY Compost Tea Brewer and Compost Tea

Simply stated, compost tea is a water-based solution that has been amended by adding compost and other nutrients. This solution then “brews” or steeps in water (not over any heat source) thereby enabling all the wonderful microorganisms in the compost to leech into the liquid. This leaching infuses the solution with all the goodness any garden can desire!

Think about the tea you make in a teapot where the tea in the tea bag is replaced with compost. The logic is of course that if the compost added to the soil is beneficial, then so is the water that has been infused with the same beneficial microorganisms. If you are serious about your organic garden, regular applications of compost tea will add to the health and well-being of your soil. Think about the benefits that probiotics provide to your body; compost tea provides similar benefits to your plants and soil.

What Are The Two Types of Compost Tea?

Basically, there are two types of compost tea: 1) Passive or 2) Actively Aerated Compost Tea (AACT). Both provide benefits to your soil and “passive” tea is very simple and inexpensive to make. But research has shown that AACT provides an added turbo boost to the solution that is filled with the beneficial microorganisms that are so beneficial to your soil and plants.    

Passive Tea

Passive tea is made by basically dumping a load of compost into a bucket of water and stirring it about on occasion to release the microbes from the compost into the water You then let it sit for a short time to enable the microbes to work their way throughout the solution.

Actively Aerated Compost Tea (AACT)

Actively Aerated Compost Tea (AACT) is a “tea” that is made by adding compost to a solution of water, but in this case, we add nutrients – e.g., black-strap molasses, liquid kelp, hydrolyzed fish, etc –  and oxygen to the water to feed the beneficial microorganisms with the goal of enabling them to reproduce, multiply aggressively and supercharge our “tea”.  There has been extensive research on the benefits of compost tea and the science seems very clear; AACT provides far more beneficial organisms in your tea than does the passive alternative.   This video shows the active aeration of our tea.

What’s the difference between compost and compost tea?

We use both compost and compost tea in our garden, as they both have their place.  Your soil structure will benefit from actual compost as it helps bind the soil particle aggregates.  Compost-rich soil is more aerated with air tunnels that enable your soil to retain air, moisture, and nutrients.  Actual compost helps amend sandy soils to retain more moisture and nutrients and helps loosen the clay particles in heavy clay soil to improve aeration.  

Both compost and compost tea add and feed the important microbe and insect life in your soil.  This is an important observation: The more alive your soil is, the healthier it is.  Think of your old-growth forests and all the life teeming on the forest floor that feeds on the decaying leaves and other organic matter.  That’s your goal for your garden soil.  

Where compost tea and compost differ is in a couple of ways:  Because the tea is in a liquid form, it’s easier to distribute on a regular basis, especially on a lawn or similar area.  As a foliar application, compost tea distributes these helpful microbes on the leaf and stem surface, which can then crowd out less beneficial pathogens.

In a nutshell, compost tea is a liquid concentrate that aids the health of your plants, roots, and soil and increases nutrient uptake.  Compost tea will not replace the need to fertilize but will make the fertilizer work better. Finally, and possibly most importantly, the actual brewing process feeds and energizes the beneficial microbes in the compost.  So, when you do apply them to the soil, they’re in NASCAR mode.

Why is it good for my garden?

The production of any garden is only as good as the health of the soil from which it grows.

The real benefit of compost tea is that while it does provide some plant nutrients inherent in the compost to the soil,  more importantly, it introduces a wealth of the kind of beneficial microorganisms to your soil that foster the very decomposition process and feeding cycle that provides more usable and sustainable nutrients for your plants. It’s quite possible that your soil is filled with organic matter and nutrients that are not in the form most beneficial for your plant to use. We are all familiar with how yogurt helps your body by providing probiotics (good bacteria). Compost tea is similar in that it helps your plants and soil by providing good bacteria and fungi.

Compost Tea is Like Yogurt for Your Garden

The microorganisms in compost tea provide the basis by which organic matter and chemical nutrients are broken down into usable plant food and an efficient and effective soil life cycle. Making compost tea a great tool to replenish barren soil or even just introduce a wider variety of bacteria, fungi, and protozoa that are the basic foundation upon which organic decomposition takes place. This was EXACTLY the case with our garden soil.

The soil analysis provided by the local organic garden store that we referenced here showed us that we had an adequate organic matter in the soil and we fertilized regularly but our soil was “constipated”! The organic matter was not in a form usable to the plant as nutrients.  There is a school of thought that drenching the foliage of your plants with tea also benefits the plants by coating the leaves with beneficial organisms. These beneficial organisms then “crowd out” more harmful elements making your garden less susceptible to disease. While there are many believers, the science is still inconclusive on these claims. But, as it relates to benefits to the soil, the science is clear and compelling.

As I mentioned in the opening, we’ve been actively growing an organic veggie garden for over 15 years. We began adding 25 gallons of compost tea to the soil AND foliage twice weekly about 5 years ago. Our plants have never been more lush, healthy, and productive. Compost tea is becoming more available from commercial sources with each passing day.  Here are some options:

Brew Your Own

We use a large amount of compost tea in our garden. You can’t apply too much tea to your garden – unless of course – the soil is oversaturated to begin. But under normal conditions, you can’t “over tea” your garden. We use approximately 50 gallons a week on our 130 square foot garden – that works out to about 3/8 a gallon per square foot. Do your own calculations for the size of your garden to determine your needs.

It became clear that because we use such a large amount, we would be better served by brewing our own tea. There is a large number available online but here is the DIY Compost Tea Brewer that we use. Keep in mind that the quality of your compost tea is only as good as the compost from which it is made. Bad Compost = Bad Tea. However, if you don’t want to or can’t make your own compost there are many, many “how-to’s”, commercial sources of compost and compost tea brewers for sale – all sizes, shapes, and costs. Here is one I found on Amazon.

Please note, I have not tested this compost tea brewer myself, so this does not represent any kind of endorsement for it. But, the elements are all very similar and simple; a vessel to contain the solution, air pump, and tubing to introduce oxygen to the solution and nutrients to feed the microorganisms.  As you can see, some of the larger brewers are quite expensive.  

Rather than make such a large expenditure I asked my husband to make one for Mother’s Day! You can see what he used to make our compost tea brewer and how he made it here.

You can also find compost tea for sale online from of a variety of suppliers

A quick check on Amazon yields a variety of types, sizes, and prices:

Compost Tea and Tea Bags:

In most areas, you can find a garden store that brews their own and offers compost to tea for sale to consumers. Our local organic garden store sells high-quality tea for $1.25 a gallon or so. Many stores also offer compost tea brewers for sale.  Check your local garden store for their offering.

Now that you’ve finished this post, if you’d like to make your own, then read How to Make a Compost Tea Brewer. Then mosey on over to read How to Brew and Distribute Compost Tea.

Bookmark this page or pin the following image to refer to this discussion on Compost Tea in the future.

pouring compost tea on the vegetable garden

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  1. I tried composting, didn’t work for me (I think because I was terrified of finding bugs in it) so it’s awesome that you can buy the compost tea too! Thanks for sharing!

    1. Oh Millie, that makes me laugh. Compost is definitely bug-friendly and luckily I really don’t mind bugs at all. In fact, the more earth worms the better in my book. Hope you get some compost tea for your garden.
      Hugs, Lynn

  2. La méthode est intéressante ; mais est ce que les déchets de légumes (cuisines) peuvent être utilisés comme compost si
    1) couper on petits morceaux
    2)sécher ce produit au soleil
    3) déposer la couche de ce produit puis une couche de sable
    ou il faut le broyer

  3. Hi Lynn,
    Thank you for this amazing piece on compost tea. I have been trying to make compost tea but I learned a different way. I found the recipe in a homesteading book. It said to collect veggie scraps and garden clippings and add into water. Let sit for 7-10day stirring every day. It ended up smelling so so so bad. and I’ve been hearing different things about the bad smell. Some say it’s still good for plants but not for worms. Others have said bad smell = bad bacteria and it’s unsafe to use in the garden. What are your thoughts on bad smelling tea using my method? And is this method even effective? Regarding your method, which is the actual making of “compost” tea, I was wondering if the bacteria and microorganisms (that are aerobic) in the compost drown/ die when submerged in water where the environment becomes mostly anaerobic? Or does it not become anaerbic because of the air bubbles? Thank you for your help!

  4. Hi Klara, thanks for visiting us! That is a great question. The foul smell means that your tea has likely gone anaerobic – due to lack of sufficient oxygen. Throw it out as it can introduce harmful pathogens into your plans and soil. Healthy tea will have an earthy, soil like smell. Many people brew tea the way that you learned. That method is called passive tea. The most important element of the passive method is to stir regularly – if the solution becomes oxygen deprived for any stretch of time, it will quickly become anaerobic and unhealthy to our soil and plants.

    The method that I prefer is the actively aerated method (AACT) wherein you supply oxygen and nutrients to enable the microorganisms in your tea to multiply and thrive. The continuous supply of oxygen prevents your tea from “drowning” or becoming anaerobic. There has been alot of research that has shown that the AACT method is much more effective in developing the beneficial microorganisms that help our gardens flourish.

    Happy gardening!

  5. Ohh I see! Thank you so much, Lynn! That was super helpful! <3
    The only problem is, I followed someone else's advice and mixed that horrible smelling tea in my garden. I mixed it in quite a bit and let it sit about 1-2 weeks before planting. Am I doomed?

    1. Hey Klara! I don’t think you’re doomed. Some anaerobic solutions respond quickly when reintroduced to better aerobic conditions – in fact there are many people that swear by the benefits of anaerobic tea…I’m just not one of them. If you do have any concerns, I would contact my local county ag extension office for more information. Happy gardening!

  6. At any point, should the entire tea bucket be dumped and renewed? or, with regular feedings of molasses, can it keep going indefinitely?

    1. Hi Deborah, We have always used the entire supply and washed the equipment, so I can’t speak from experience. But, if you keep feeding and kept up the oxygen supply going, I don’t see it couldn’t be sustained. At the end of the day, trust your nose. If it smells earthy, it is probably still good. But if it begins to smell rancind or rotten, I would dump it, wash the equipment and start again.

      I hope this helps.


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