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Spraying compost tea in the garden

Compost tea provides plants and gardens with a metric buttload of life-giving beneficial microorganisms.

But it takes a special approach to brewing to get the most beneficial biology from your compost tea.

So we’re going to give you the ingredients, recipes and process to brew high-biology compost tea at home.

Compost Tea Ingredients

Ingredient 1: Water, The Source of All Life

Quality compost tea starts with clean water.

Fresh spring water, harvested rain water, or well water is the best. City water will likely contain chlorine or chloramine. Water treatment plants use these chemicals to kill any bacteria, viruses, or parasites that may be present in the water before it gets to your home.

water in a barrel to make compost tea

We’re trying to enhance the populations of bacteria and other microorganisms through the compost tea brewing process. So we’ll need to treat any water that may contain chlorine or chloramine.

Letting the water sit for 24-48 hours will off-gas any chlorine. Agitating the water with your air pump will accelerate that process as will exposing the water to sunlight.

Acids can also neutralize chlorine and chloramine. And as luck would have it, we happen to use humic acid as a food for microorganisms to brew compost tea! Humic acids form as a result of the humification process and are a common element found in soils and compost.

It doesn’t take much humic acid to bind up all the chlorine or chloramine in water; just enough to make the water tinted slightly brown.

This amounts to a few drops of humic acid for a five-gallon brew. I like to incorporate humic acid into all of my compost tea brews. The humic acid not only neutralizes any chlorine or chloramine in the water, it also feeds soil biology and enhances nutrient uptake in the soil.

More on humic acid below.

Ingredient 2: Oxygen-Rich Air

The microorganisms we want to promote through brewing compost tea are aerobic microbes, meaning they require oxygen to survive.

So you’ll need an air pump to keep the water agitated. Air pumps feature labels describing their output, usually in LPM or “liters per minute.”

A good rule of thumb is to choose a pump with an output of one liter per minute for every gallon of compost tea brewed.

For example, a 50 gallon brewer will work best using a pump with an output of 50 to 60 liters per minute.

The air will need to travel through the entire column of water in order to keep all of the liquid aerated and agitated. Simply agitating the surface will not suffice.

A full-column oxygenation will keep the microorganisms flourishing and reproducing, without any anaerobic pockets forming in the brewer.

Ingredient 3: High-Biology Compost or Vermicompost

High-biology compost tea is not possible if the compost you’re using doesn’t contain much life.

Compost from large-scale operations like municipal-type composting facilities generally don’t house a healthy population and diversity of beneficial microbes. These facilities are normally not focused on quality of the compost; they are trying to make a product and get it out the door.

Backyard compost may or may not have the life you are wanting for compost teas.

Compost piles with noxious odors emitting from them are most likely breeding anaerobic microbes that could cause problems if brewed and applied to plants. On the other hand, compost that has aged for a year or two and smells of rich earth is more likely to be full of beneficial biology that your plants will love.

The only way you can truly know what life is in a compost is by examining it with a microscope. (Hey, we can do that for you!)

When it comes to beneficial microorganisms, vermicompost usually always contains greater quantities of life than regular compost. Worms consume organic matter coated with bacteria, fungi, and protozoa.

Their digestive tracts contain even more species of bacteria. The castings coming out of their rear ends are coated with not only more beneficial bacteria but often plant growth hormones as well.

All of these help to support plant life.

Ingredient 4: More Food for the Microbes

I like to stick with just a few main sources of foods for microorganisms: humic acid, fish hydrolysate, and soluble kelp.

Humic Acid

Humus is a term for soil organic matter that has been fully broken down into complex, stable compounds that resist further decomposition. And humic acids, along with fulvic acids and humin, are formed through the process of humification which produces humus.

Commercial humic acid products are generally sourced from leonardite which is made up of ancient decomposed plant and animal matter. Leonardite is mined and turned into a powder or liquid form.

Fish Hydrolysate

Fish hydrolysate is basically ground up, liquefied fish. (Yummy!)

It contains all of the fats and oils from fish which provide amino acids which become food for fungi. Fish hydrolysate is full of nutrients and micronutrients. Full of macro nutrients and micronutrients, fish hydrolysate is different from fish emulsion, which is also commonly found for sale in garden centers. Fish emulsion has had the fats and oils removed, making it less expensive than fish hydrolysate.

Soluble Kelp

The ocean is an underwater macrocosm of life.

When terrestrial beings die and decompose, they turn into soil. Oceanic life decomposes and gets dispersed throughout the ocean. As kelp grows in the water, it absorbs the vitamins, minerals, and other nutrients from these decomposed life forms.

Note: Look for soluble kelp as opposed to kelp meal. Kelp meal will remain granular and can clog your spraying equipment whereas soluble kelp will fully dissolve in water and will be easily accessible to microorganisms.

Soluble kelp is an excellent source of minerals, nutrients, and micronutrients.

Compost Tea Brewers

The last thing we will need to brew compost tea other than clean water, a source of air, and compost/vermicompost is a brewer. For most growers it doesn’t have to be more than a five gallon bucket. Check out the Urban Worm Guide to Compost Tea Brewers to learn all about setting up your own compost tea brewer.

In Case You Missed It…..

The Urban Worm Company’s “soil nerd” Troy Hinke wrote an awesome guide to compost tea brewers, helping you build a 50-gallon DIY brewer or guiding your choice of commercially available brewers.

Compost Tea Recipes

A good general compost tea recipe promotes a healthy amount of both bacteria and fungi.

The main organisms that multiply during the brew process are bacteria and protozoa. Bacteria can double somewhere between every 12 minutes and 24 hours. Yeah, there’s a huge difference between 12 minutes and 24 hours but the speed with which a population doubles depends on the classification of bacteria.

Protozoa multiply nearly as fast.

Nematodes takes a little longer as they reproduce by laying eggs, which hatch into larvae. So don’t expect a drastic increase in nematodes during the brew process.

Same for fungi. The agitation of the brew process will be too much for fungal hyphae to grow in the solution.

But why, pray tell, do we add fungal foods to compost tea?

That’s because we want to give those tiny fungal hyphae something to feed on after the compost tea is applied to plants and soils.

So how do we make this fresh goodness?

Below are recipes to get you some really solid compost tea, whether you’re brewing 5 gallons or 50.

Five Gallon Brew

Fifty Gallon Brew

If you cannot find one of the ingredients, simply omit it.

If using a fish/kelp combo like Neptune’s Harvest, then use one part for each ingredient called for.

For example, if the recipe calls for 1 tbsp of fish hydrolysate and 1 tbsp of kelp, use 2 tbsp of the fish/kelp combo.

The Compost Tea Brew Process

Compost Tea Brew Step 1: Prep the Water

The first thing to do is to get the water ready in the brewer and allow it to come to the ambient temperature.

Compost tea should be brewed in the same ambient temperature as the plants that the compost tea is intended for.

If the plants are in a greenhouse, brew in the greenhouse. If the plants are outdoors then brew outdoors. Fill your brewer and allow the water to sit for at least 6-12 hours in order to get to ambient temperature.

To begin the brew process, I like to add microbial foods to the water before introducing the compost.

I will start the air pump to get the water moving around which will assist in mixing the foods into the water.

Then I add my humic acid, fish hydrolysate, and kelp to the water.

Compost Tea Brew Step 2: Increase Surface Area of Compost & Vermicompost

After introducing the microbial foods to the water we are ready for the compost/vermicompost.

I combine vermicompost, fresh compost, and aged compost to increase the diversity of microorganisms.

Place the compost or mix into the compost tea brew bag. Before closing the bag, it is good to massage the compost and brew bag inside the brewer.

Place the brew bag with compost into the brewer.

Hold the brew bag with one hand and use the other hand to reach into the bag, grabbing any chunks of compost and breaking them up. Massage the compost and work it up against the sides of the bag. We are wanting to get all of the compost broken apart to expose as much surface area as possible.

The agitation of the water will help to further extract microorganisms from all of this organic matter.

After massaging the compost on the inside, close the bag and work it more from the outside.

Squeeze the bag and roll it between your hands. Spend a good three minutes massaging the compost in this way. It will benefit the compost tea by extracting more microorganisms.

Now hang the brew bag on the brewer and you’re officially brewing compost tea!

Compost Tea Brew Step 3: Set Your Brew Length

The idea behind brewing compost tea is to extract microorganisms from compost, give them foods to eat, and let them rapidly reproduce. We start off with say 100,000 microbes and want to make those into 100,000,000 microbes.

There is a point where the compost tea brew will hit a peak population of microorganisms. Soon after, anaerobic microbes begin to multiply and speedily turn the brew anaerobic.

The length of the brew time will be dependent on the ambient temperature.

Colder temperatures depress microbial activity. Hotter summer months get microbes moving and reproducing much more quickly.

When temperatures are getting into the 90’s F and higher, it will take 12-24 hours to reach peak populations. Cooler temps mean longer brew times, anywhere from 48-72 hours.

The ambient temperatures listed above are an average between daytime and nighttime temps. Use this table as a rule of thumb only.

It is much better to err on the side of brewing for less time, producing a smaller population of aerobic microorganisms than an altogether anaerobic brew.

Advanced Tip: Add Straw to Infuse with Protozoa

In the book Teaming With Microbes, Jeff Lowenfels describes making a “protozoan infusion” using green plant material and aerated water. I took this idea and tweaked it a bit to add more protozoa to a compost tea brew.

For a small 5-gallon brew, you can grab a tiny handful of straw, only about 15-20 strands is good enough!

Add this to the brew bag during the last 6 to 12 hours of brewing. The added protozoa will help to increase nutrient cycling through predator/prey interactions with bacteria!

Compost Tea Brew Step 4: Empty the Brewer

After emptying, I set my brew bag aside until I am ready to clean the brewer.

Run the brewed compost tea through a filter to remove large amounts of sediment if using any type of sprayer or applicator that might clog.

You can use the brew bag for this filtration or have a second brew bag ready to use as a filter.

Empty the compost tea from the brewer into your spray tank or transfer tank. If only pulling a small amount of compost tea at a time from the brewer, I suggest keeping the brewer aerated until using all of the contents.

After completely emptying the brewer, it is wise to clean it as soon as possible. It will be much easier to clean using a hose and small scrubber while the brewer and leftover debris are still wet.

Compost Tea Brew Step 5: Clean the Brewer

I like to use a small, green Scotch-Brite scouring pad and a hose to clean my brewer. It is best to use environmentally-friendly dish soap if you are dealing with sticky residue on the brewer walls.

You can also use hydrogen peroxide in a spray bottle to remove all residue and microbes that may be attached to the brewer.

A scrub brush and dish soap works best to clean the brew bag.

Be sure to turn it inside-out to get all surfaces!

Advanced Tip: Save & Reuse That Compost

After the brew is over, empty the contents of the brew bag back into your compost pile or worm bin.

This organic matter is chock full of both microbes and the food to sustain them. In other words, it’s the perfect compost inoculant.

Your spent compost isn’t really ready to retire. It’s just entering its prime!

Compost Tea Brew Step 6: Use Your Tea….Like…..Now

Your tea is on borrowed time.

We need to apply the very lively compost tea while all of these aerobic microorganisms are thriving. If you wait too long, the microbes will consume all of the oxygen and the brew will go anaerobic.

Once the brew is complete, the teas needs to be applied to plants and soils within 24-48 hours to be of the most benefit.

Hotter temps mean more microbial activity which shortens the brew time, but it also shortens the length of time your tea is good for.

For summer months, use compost tea closer to the 24 hour time frame.

For cooler months in the spring and fall, it may last a bit longer. Either way, you won’t want to put the compost tea in a tank or bottle and let it sit around for a few weeks before you get around to applying it.

Applying Compost Tea

Tea can be applied with anything from a watering can to a tractor with a boom sprayer. It can be used as a foliar spray and soil drench, or other creative ways. During my time at Rodale Institute, I started a hydroponic system using only a liquid compost solution as the source of fertility.

All of these will be discussed in a future blog post by the Urban Worm Company. Stay tuned!

This article was co-written by the Urban Worm Soil Biologist Troy Hinke, a Soil Food Web trained expert in soil microbes. Check out his What’s Brewing Podcast on Apple Podcasts and Spotify.

If you want to know if your soil is appropriate for your crop, or if you need help our help with anything else, engage our services today!