How to Make and Use Compost Tea Fertilizer

Most gardeners know that a good heaping handful of well-rotted compost is an excellent soil conditioner and fertilizer.

It’s all natural so adding it to your garden won’t harm waterways or soil microbes, and it contains all the nutrition plants need to thrive.

You may have even heard of compost tea, which harnesses the awesomeness of compost and takes it up a notch.

But it always surprises me that most gardeners I know have never tried making their own.

That’s a shame because it’s very easy to brew and provides a boost to your crops and ornamentals without the use of chemicals. Once you make a batch, I think you’ll be converted.

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Humans have been making compost tea since the early Egyptian, Greek, and Roman times. The primitive bucket methods used then are the ones many of us still employ today.

Of course, there are also a number of modern adaptations to help us make our compost tea even better and easier to brew.

A good mixture contains all the nutrients you’ll find in a chemical fertilizer, plus more, with none of the bad stuff.

Compost tea contains the “big three” macronutrients: nitrogen, phosphorus, and potassium, along with micronutrients such as copper, zinc, iron, manganese, humic acids, salicylic acid, and beneficial metals.

There are also beneficial protists, fungi, yeast, and bacteria that not only benefit your plants but help to improve the soil as well.

The first time I tried using compost tea in my garden was when I bought some from a brewer at my local farmer’s market. This was back in the 90’s and compost tea was firmly in the category of “crunchy granola” gardening. I started using it and noticed an improvement in all of my plants.

Anecdotally, I conducted an experiment by using it on half of my tomatoes and used my good old reliable store-bought fertilizer on the other half.

You’d better believe after that little experiment, I started figuring out how to brew my own as the results were clear – my tomatoes grew much better with compost tea!

If you want to do the same, this guide will help you make it happen. To do that, we’re going to talk about the following topics:

What Is Compost Tea?

The easiest way to think of compost tea is to imagine a cup of tea, but instead of steeping tea leaves in the water, you’re going to steep compost.

You can always just nab some compost out of your bin, but serious growers create specific recipes that prove to be beneficial to plant growth and soil health. You can also use vermicompost from your worm farm.

There are many different kinds, but non-aerated (NCT) and aerated (ACT) are the two most common. You’ll also find anaerobic and fermented types, though these are different enough from the first two that gardeners sometimes consider them separate products.

Aerated compost tea contains the right oxygen content to allow all the beneficial microbes that were originally in the compost to continue to thrive.

These beneficial species have a positive impact on your garden, suppressing bad pathogens and supporting good microbes.

A good aerated tea contains beneficial nematodes, bacteria, fungi, and protozoa that will benefit your plants and garden.

Non-aerated tea is extracted without providing aeration, resulting in fewer active microorganisms.

Anaerobic tea has little oxygen, dramatically altering the composition of the microbes.

Fermented tea often includes whole, undecomposed materials from the compost pile, like weeds or other plant matter that break down during the fermentation process.

Typically, the oxygen levels are low in this type of tea.

Both anaerobic and fermented tea are significantly different from ACT and NCT, and we won’t discuss them much further here. We’ll focus on how to make your own ACT and NCT.

Don’t confuse compost tea with manure tea, compost extract, or bacterial soup. These all have their uses in the garden but aren’t the same.

Why Use Compost Tea?

The most obvious reason to make and use compost tea is because it’s incredibly nutritious for your plants. It’s a low-cost, effective way to feed your vegetable crops and ornamentals.

It’s also much better for the environment than conventional fertilizers, both in its production and once added to the soil.

Plus, it can even protect your plants from some of the pathogens out there that wreak havoc on your garden.

One study by Ana Isabel Gonzalez-Hernandez et al at the University of Salamanca in Spain, which was published in the journal Agronomy, in 2021, found that compost tea could protect pepper plants from the pathogens Phytophthora capsici and Rhizoctonia solani.

Can your conventional fertilizer do that? No. The answer is no.

Compost tea has also been used to control powdery mildew, downy mildew, gray mold, septoria, and damping off in tomatoes. In potatoes, it has proven to suppress Alternaria and Fusarium.

Inorganic, chemical fertilizers are made from salts, which are harmful to soilborne organisms because they leave salt and ammonia residue, resulting in fertilizer burn.

Compost tea also contains organic nitrogen, which is much more readily absorbed from the soil than the nitrate form of nitrogen that conventional fertilizers add.

Both can be used to feed your plants, you just need less if it’s in a form that the plant can use more readily.

How to Prepare

First and foremost, the old adage “quality in quality out” applies here. If your compost is poor quality, your tea will be poor quality.

If you’re new to composting, you can read an excellent rundown about how to start and maintain a healthy compost pile in our guide.

It’s vital to avoid adding contaminants that contain pathogens or pests. Your goal is to create a positive environment for all kinds of creatures to flourish.

We want to nurture the beneficial microbes, but if bad ones are present, they will also be able to reproduce.

For example, if you have root-knot nematodes in your garden, and you pull the infected plants and put them in your compost, you run the risk that the pests will proliferate, infecting more plants when you apply the compost.

You also need to avoid anything that might contain human or animal pathogens. You don’t want to be saturating your soil with E. coli or salmonella. Never add contaminated materials to the pile, and keep it covered to prevent bird or rodent feces from getting in.

Before making your tea, the compost should be well-rotted and thoroughly mature.

Compost that isn’t sufficiently well-rotted can harbor pathogens and may lack many of the good microbes that you want to add to your garden, like beneficial fungi, bacteria, and protozoa.

Your compost should have reached temperatures of between 90 and 110°F to kill off most of the destructive pathogens.

The other component to your brew is good-quality water. Rainwater is ideal, but you can also use municipal water, so long as you remove any chlorine.

If you need to get rid of chlorine, stir or blend the water vigorously for 30 minutes. Or, you can use a bubbler, letting it run in the water for about six hours.

You can also boil the water for 30 minutes or filter it through charcoal carbon filters. Finally, you can simply leave the water in an uncovered container for 24 hours to allow the chlorine to evaporate.

Aerated

As mentioned, just as the quality of the compost you use is important, so is the quality of your water.

Chlorine, heavy metals, or contaminants will ruin your tea. If you’re not using rainwater, make sure you filter or aerate your water to remove chemicals before use.

If, at any point, the tea starts to smell foul, the oxygen has likely been depleted and the materials are rotting. Check your mixture daily for rotten egg, vinegary, sour, or otherwise “off” odors. If this occurs, toss it and start over.

Foam, on the other hand, is a good thing. It means proteins, amino acids, and carbohydrates are being produced. Tea made from vermicompost tends to be particularly foamy thanks to the leftover worms in the mix.

Non-Aerated

Non-aerated tea doesn’t have the same variety of living microorganisms as aerated, but it can still provide a lot of nutrients and some degree of disease control.

Why would you want to use NCT if ACT is better? Good question!

The answer is that NCT is much easier to make. You simply fill a bucket halfway with clean water and then add compost within an inch or two of the top.

Skip the stirring or bubbler and just let it sit. It will take longer to steep and won’t be ready for about two weeks, but you can literally set it and forget it, just checking on it periodically.

Just keep it in a cool area out of direct sunlight until you’re ready to filter all the solids out.

You do need to be extra diligent about sniffing the mixture and watching for the development of molds on the top with non-aerated mixtures.

Don’t wait much longer than two weeks because, at that point, bad pathogens might start to outcompete the good ones.

Filtering

Once you’ve brewed your tea you’ll need to filter out any solids before applying the liquid to your garden.

The trick is to find some mesh that isn’t so large so that everything passes through but isn’t too small so that beneficial components can’t get through.

Be sure that the container you’re filtering the compost tea into is clean. You don’t want to contaminate your pristine liquid after all that hard work.

Let the mixture settle for an hour or so after stirring or turning off the bubbler.

Of course, if you used a bag to contain the compost, all you need to do is lift it out. Give it a good squeeze to get the last of the liquid out.

You can put the discarded solids back into your compost or use as a mulch for your plants.

Application

You can apply the finished product either to the soil or directly onto the foliage of the plants.

For foliar applications, it can be applied at full strength or diluted in water.

If your municipal water is chlorinated, use rainwater or remove the chlorine from your water as discussed above.

The ideal ratio is about one part tea to four parts water, but feel free to play around.

If you are applying it as a foliar spray you want to cover about 75 percent of the leaf surface on both sides.

A general rule of thumb is to use about five gallons for each acre of plants. Don’t apply during the hottest part of the day or when it is raining, though a light mist is fine.

As a soil drench, use about one pint per plant.

It can be used both for potted and in-ground plants and for those growing indoors, outdoors, or in greenhouses.

Any way that you can apply water can be used to apply the tea. You can pour it onto the soil using a watering can, put it in your drip irrigation, use a hose end or hand spray, feed it through sprinklers, or just scoop a little out of the bucket.

The oxygen in the tea starts to drop considerably after six to eight hours, so it’s best to use the fresh tea right away. If you can’t, store it in a cool area out of direct sunlight for up to five days.

Both drenching the soil and foliar sprays work for suppressing disease.

I want to add a word of caution, here. I wouldn’t rely on your tea alone as a method of treating disease. The brews can vary wildly in their composition of beneficial organisms depending on your compost, water, and brewing method.

At best, it’s usually best reserved for use as a short-acting preventative against some diseases.

Regardless, it’s always an effective fertilizer, feeding your plants and your soil without introducing potentially harmful chemicals. Plus you don’t have to worry about fertilizer burn!

Optional Additions

Your healthy garden compost alone makes for excellent tea, but if you want to try a few different recipes to see how each improves the growth of your plants, there are lots out there.

A good starting recipe is 30 parts compost, two parts unsulfured molasses, one part kelp, and one part any fruit juice, or leftover pulp from a juicer. Don’t use any juice with additives or preservatives in it. It must be pure juice or pulp.

Leave out any sugars like molasses or fruit if you’re making non-aerated tea. These will just cause your mixture to ferment rather than steep.

It’s Tea Time!

Now, after all this work, you might be wondering why you don’t just use compost in your garden.

Well, for starters, you can’t spray compost onto the foliage of your plants.

You also can’t use it as a targeted root treatment in the soil. Plus, you can’t add and steep all the extra goodies like humic acid.

When you look at it that way, it seems like the little bit of extra work is worth it, right? I bet when you see the improvement in your garden you’ll be totally sold. At least, I know I was – and still am.

Do you have a compost tea recipe that you’ve perfected? Or maybe one that you’re going to try? Share with us and other gardeners in the comments section below!

In case you couldn’t tell, I’m a compost tea convert and I hope that this guide helped bring you over to the tea side. I also hope that it helps you feel confident in making your own.

And if you’d like to read more about composting, we have several guides for you to add to your reading list: